GIFT  OF 
Dr.    Courtney  Gee  Clegg 


/x 


3^ 


CHEMICAL  MANIPULATION, 


BEING 


INSTRUCTIONS 


STUDENTS  IN  CHEMISTRY, 


THE  METHODS  OF   PERFORMING  EXPERIMENTS  OF  DEMONSTRATION 
OR  OF  RESEARCH,  WITH  ACCURACY  AND  SUCCESS. 


BY 

MICHAEL    FARADAY, 

F.R.S.,  M.R.I.,  &c.  &c. 


FIRST  AMERICAN,  FROM  THE  LAST  LONDON  EDITION, 
EDITED  BY 

J.  K.  MITCHELL,  M.D. 

LECTURER  ON  MEDICAL  CHEMISTRY  IN  THE  PHILADELPHIA  MEDICAL  INSTITUTE. 


PUBLISHED  BY  CAREY  AND  LEA. 
1831. 


•    '  » 

. 

H 


Entered  according  to  the  act  of  congress,  in  the  year  1831,  by  Carey  and 
Lea,  in  the  clerk's  office  of  the  district  court  of  the  eastern  district  of  Penn- 
sylvania. 


•M 


Philadelphia: 

Printed  by  James  Kay,  Jun.  &c  Co. 
No.  4,  Mjnor  Street. 


TO 


PROFESSORS 
SILLIMAN,    AND   HARE, 

WHO  HAVE  SO  SIGNALLY  ADVANCED  THE  INTERESTS  OP  THE  SCIENCE  OF 
WHICH  IT  TREATS, 


American  Etu'ttou 


THE  WORK  OF  MR  FARADAY 


IS 


RESPECTFULLY  DEDICATED. 


J.  K.  MITCHELL. 


*  * 


. 

PREFACE 


TO 


THE   SECOND   EDITION 


MY  reason  for  venturing  to  add  a  new  work  on  Chemistry  to 
the  many  excellent  productions  which  previously  existed,  was 
because  there  seemed  to  be  a  deficiency  in  the  particular  kind 
of  instruction  which  it  was  my  intention  to  convey.  In  the 
execution  of  my  task  I  endeavoured  to  make  every  other 
point  subordinate  to  the  one  of  embodying  a  mass ( of  useful 
information  on  the  practice  of  Experimental  Chemistry.  Be- 
ing intended  especially  as  a  book  of  instruction,  no  attempts 
were  made  to  render  it  pleasing,  otherwise  than  by  rendering 
it  effectual;  for  I  concluded  that,  if  the  work  taught  clearly 
what  it  was  intended  to  inculcate,  the  high  interest  always  be- 
longing to  a  well  made  or  successful  experiment,  would  be 
abundantly  sufficient  to  give  it  all  the  requisite  charms,  and 
more  than  enough  to  make  it  valuable  in  the  eyes  of  those  for 
whom  it  was  designed.  It 

It  may  well  be  supposed  that  the  confirmation  of  my  opinion 
by  the  necessity  of  a  second  Edition  of  the  work,  affords  me 
no  slight  pleasure,  and  I  feel,  even  more  than  I  did  at  first, 
the  propriety  of  the  view  which  I  had  taken  of  the  character 
of  the  instruction  required. 

In  the  present  edition  I  have  made  many  corrections  and 
alterations,  without  enlarging  the  book;  for  although  I  have 


vi  AUTHOR'S  PREFACE. 

always  felt  that  much  valuable  instruction  in  Manipulation  had 
been  omitted,  yet  deeming  the  utility  of  the  work  to  depend 
greatly  on  its  limitation  to  a  moderate  size,  I  found  it  impossi- 
ble to  introduce  any  additional  matter  without  displacing  that 
which  was  more  important;  nor  do  I  anticipate  that  I  shall  in- 
cur blame  by  withholding  that  which  has  not  been  tried,  and, 
in  my  own  judgment,  is  of  less  moment  than  that  which  ex- 
perience has  proved  to  be  useful  and  desirable. 

M.  FARADAY. 


m 
OBSERVATIONS  PRELIMINARY 


TO 


THE    AMERICAN    EDITION 


To  the  practised  chemist,  this  work  of  one  of  the  most  pro- 
found and  skilful  philosophers,  must  be  highly  acceptable,  be- 
cause it  suggests  even  to  him  much  that  is  peculiar:  but  to  the 
young  adventurer  in  the  wide  and  difficult  field  of  practical 
chemistry,  there  has  never  been  presented  so  valuable  a  gift  as 
the  elaborate  volume  of  Mr  Faraday.  Hitherto  that  detail 
which  is  now  published,  was  confined  to  laboratories  of  the 
first  class;  and  much  of  it  to  that  laboratory  in  which  Davy 
achieved  his  splendid 'victories  over  refractory  matter,  and 
Brande  and  Faraday  so  signally  accelerated  the  progress  of 
science.  Such  knowledge  was  supposed  unattainable  except 
in  the  laboratory  itself,  and  that  too  only  after  years  of  patient 
and  laborious  attention.  There  it  is  perhaps  even  now  to  be 
acquired  in  the  most  perfect  degree;  but  even  there,  by  means 
of  the  present  work,  its  acquisition  will  cost  the  instructor 
much  less  labour,  and  the  pupil  much  less  time.  With  such  a 
work  in  his  hands,  and  any  good  treatise  on  chemistry,  the 
student  who  is  debarred  access  to  a  great  practical  laboratory, 
may  succeed  in  accomplishing  himself  highly  in  the  delicate 
business  of  manipulation,  and  even  become  skilful  in  the  higher 
departments  of  analysis. 

In  the  United  States  there  is  not  a  single  laboratory  devoted 


Vlll  PRELIMINARY  OBSERVATIONS. 

to  the  instruction  of  students  in  analytical  chemistry,  and  he 
who  desired  superior  skill  in  that  department,  was  compelled 
to  look  for  it  in  European  institutions.  Few  being  able  to  bear 
the  pecuniary  expense,  the  number  of  well  educated  chemists 
has  beea,  in  our  country,  surprisingly  small.  It  is  in  this  man- 
ner that  we  must  account  for  the  ignorance  under  which  we 
have,  until  very  recently,  laboured,  respecting  the  mineral  trea- 
sures of  our  favoured  country.  The  gold  of  the  south  lay  on 
the  very  surface  of  the  earth  for  centuries  unnoticed,  although 
it  was  diffused  from  Virginia  to  Florida.  By  improving  our 
skill  in  the  science  which  is  mainly  devoted  to  the  development 
of  the  hidden  riches  of  the  mineral  kingdom,  we  may  not  unrea- 
sonably suppose  that  the  national  wealth  of  that  description  will 
be  very  greatly  enhanced,  and  that  we  shall  also  free  ourselves 
from  that  dependence  on  foreigners,  in  this  department  of 
knowledge,  from  which  we  have  been  long  exempted  in  almost 
every  other.  For  these  reasons  that  work  cannot  fail  to  be 
acceptable,  which  contributes  largely  to  our  capacity  for  in- 
struction at  home,  in  a  science  of  the  very  first  importance, 
and  which  is  calculated  to  greatly  increase  the  number  of  prac- 
tical chemists,  as  well  as  to  improve  those  who  are  already 
embarked  in  its  study.  Sensible  of  tHe  great  importance  of 
the  work,  the  editor  has  reviewed  it  with  much  care,  cor- 
rected many  errors  of  inadvertence,  and  made  some  additions, 
which  seemed  to  him  likely  to  add  to  its  value.  The  profita- 
ble knowledge  acquired  by  its  perusal  in  his  own  case,  leads 
him  with  increased  confidence  to  the  conclusion,  that  the  work 
of  Mr  Faraday,  now  presented  to  the  American  public,  is  pe- 
culiarly valuable  both  for  its  intrinsic  merit  and  its  adaptation 
to  the  particular  defects  of  the  art  in  this  country. 


TABLE  OF  CONTENTS. 


INTRODUCTION 


1 


SECT.        I.  The  Laboratory       -  17 
II.  Balance  ;  weighing 

III.  Measures;  measuring  74 

IV.  Sources  and  management  of  heat 

1.  Furnaces 

2.  Lamps  109 

3.  Blow-pipes  H7 

4.  Thermometers       -  -               144 
V.  Comminution  ;  Trituration,  Mortars,  Granulation  156 

VI.  Solution,  Infusion,  Digestion     . 

VII.  Distillation  ;  sublimation  205 

VIII.  Precipitation  240 

IX.  Filtration,  Decaritation,  Washing  247 

X.  Crystallization  -         264 

XI.  Evaporation;  Desiccation  273 
XII.  Coloured  tests  ;  Neutralization  284 

XIII.  Crucible  operations  ;  Fusion  ;  Reduction  296 

XIV.  Furnace  tube  operations       -  316 
XV.  Pneumatic  Manipulation,  or  management  of  Gases  329 

1.  Pneumatic  troughs,  jars,  &c. 
B 


X  TABLE  OF  CONTENTS. 

2.  Production,  retention,  and  transference 

of  Gases                      -  337 

3.  Measurement  of  Gases  347 

4.  Of  larger  and  independent  vessels,  for 

the  retaining  and  storing  of  Gas  363 

5.  Connexion  and  Communication  376 

6.  Air-pumps,  syringes,  and  the  operations 

performed  with  them  390 

7.  Correction  of  the  volume  of  Gases  for 

temperature  and  pressure  397 

8.  Weighing  of  Gases  or  Air  403 

XVI.  Tube  Chemistry  413 

XVII.  Electricity  448 

1.  Ordinary  Electricity  448 

2.  Voltaic  Electricity  469 

XVIII.  Lutes  ;  Cements  495 

XIX.  Bending,  blowing  and  cutting  of  Glass  511 

XX.  Cleanliness  and  cleansing  553 

XXI.  General  rules  for  young  experimenters  575 

XXII.  Uses  of  equivalents — Wollaston's  scale  -         581 

XXIII.  Miscellanea  S9J 

1.  Uses  of  Corks  593 

2.  Uses  of  Paper  594 

3.  Uses  of  copper  wire     -  598 

4.  Uses  of  Glass  Plates"  598 

5.  Uses  of  Leaf  and  Sheet  Metals  599 

6.  Uses  of  soft  Windsor  brick  60 1 

7.  Conduction  of  heat      -  601 

8.  Uses  of  reflective  and  receptive  Powers         603 

9.  Writing  on  Glass  .    604 

10.  Shielling  by  a  tube  605 

11.  Engraving  on  Glass  606 

12.  Small  Air-gauges 

13.  Screens  and  Masks  for  the  eyes  and  face       611 


TABLE  OP  CONTENTS.  XI 

14.  Silvering  glass  612 

15.  Phosphorescence    -  -               614 

16.  Uses  of  Solar  Radiant  Matter  615 

17.  Magnetism            -  616 

XXIV.  A  Course  of  Inductive  and  Instructive  Practices    620 

2.  Balance;  weighing      -  621 

3.  Measures ;  measuring         -  -              624 

4.  Management  of  heat    -  -         625 

5.  Comminution  627 

6.  Solution,  digestion,  infusion  629 

7.  Distillation,  sublimation       -  632 

8.  Precipitation                 -             -  635 

9.  Filtration,  decantation,  washing  -               637 

10.  Crystallization             -  -         639 

11.  Evaporation,  desiccation    -  640 

12.  Coloured  tests  ;  neutralization  641 

13.  Crucible  operations  643 

14.  Furnace  tube  operations  646 

15.  Pneumatic  Manipulation    -  648 

16.  Tube  Chemistry  658 

17.  Electricity  662 

18.  Lutes,  cements  664 

19.  Blowing  and  cutting  of  Glass  -               665 

20.  Cleanliness  and  cleansing  666 

21.  Uses  of  the  Scale  of  Equivalents,  &c.          667 

22.  Miscellanea  667 
INDEX             -             -             -                           -  673 


A. 
f> 


• 


SECTION  I. 
THE   LABORATORY. 

1 .  As  the  Laboratory  is  a  spot  where  every  chemist  will  pass 
a  great  portion  of  his  time,  it  is  natural  that  its  arrangement 
and  furniture  should  at  first  claim  much  of  his  attention;  for, 
being  the  place  peculiarly  fitted  up  for  the  performance  of 
chemical  experiments,  fitness  for  that  purpose  must  have  ma- 
terial influence  over  the  facilities  required  for  those  practical 
exercises,  which  by  their  results  are  so  important  in  the  for- 
mation and  correction  of  his  opinions. 

It  is,  however,  very  curious,  and  at  the  same  time  instructive, 
to  remark  the  different  views  taken  by  chemists  as  to  the 
essentials  and  requisites  of  a  laboratory.  Some  will  not  think 
it  approaches  to  perfection  unless  it  consists  of  a  large  room  on 
the  ground  floor,  well  stocked  with  tables,  cupboards,  furnaces, 
and  various  other  et  cseteras ;  and  having  in  connexion  with  it 
a  seconcfroom,  dry,  comfortable,  and  fit  for  the  reception  of 
the  balance,  air-pump,  and  similar  apparatus;  and  a  third 
apartment,  which  however  may  be  a  kitchen  or  even  a  cellar, 
intended  to  contain  movable  furnaces,  bricks,  tiles,  sand,  and 
the  numerous  rough  materials  which  are  now  and  then  re- 
quired: whilst  others  will  be  satisfied  with  a  small  cupboard, 
and  think  that  sufficient  to  contain  all  that  is  required  for  their 
operations.  Much  of  this  variety  of  opinion  depends  upon 
the  difference  in  the  pursuits  of  the  persons.  He  who  studies 
chemistry  by  microscopical  experiments,  testing  the  qualities 
rather  than  ascertaining  the  quantities  of  matter,  may  find  a 
cupboard  abundantly  sufficient  for  his  operations,  or  may  even 
pack  all  his  requisites  on  a  tray ;  whilst  the  person  who  is 
engaged  in  metallurgical  processes,  in  extensive  experiments 
on  gaseous  matter,  or  in  the  application  of  chemistry  to  the 
arts,  will  find  a  laboratory  essential  to  his  progress.  Part  of 
the  difference  in  opinion  is  founded,  however,  on  mere  matter 
of  taste  and  inclination ;  and  those  who  love  the  science,  and 
C 


-                             ^ 
18  THE  LABORATORY ITS  SITUATION — SIZE. 

*  Jt    *' 

are  in  circumstances  to  pursue  it  liberally,  will  probably  never 
thinkadampkitchenorasmallatticsufficientfortheirpurpose. 
It  was  in  a  spirit  of  this  kind  that  the  late  Dr  Marcet,  when 
he  purchased  a  house  on  the  banks  of  the  lake  of  Geneva, 
which  unfortunately  he  did  not  live  long  to  occupy,  appropri- 
ated one  of  the  best  rooms  in  it  to  the  purposes  of  a  laboratory, 
not  knowing,  as  he  himself  said,  why  he  should  not  do  what 
he  could  to  make  that  a  pleasant  place  where  he  found  so 
much  pleasure. 

2.  When  the  laboratory  is  attached  to  a  public  institution, 
where  it  isdevoted  to  the  progress  and  teaching  of  the  science, 
and  where  it  is  intended  to  facilitate  the  researches  of  two  or 
three  persons  at  the  same  time,  it  must  necessarily  be  of  large 
size,  possessing  the  accompaniments  of  an  apparatus  and  a 
store-room,  and  all  the  facilities  which  have  been  found  useful 
in  variety  of  research,  and  in  extensive  operations. 

3.  Hence  it  may  be  observed,  that  in  various  circumstances, 
the  place  may  be  either  large,  of  a  moderate  size,  or  small,  and 
yet  not  in  the  first  case  exceed,  or  in  the  last  fall  short  of  what 
is  required.     In  a  volume  like  the  present  it  will  be  proper 
that  a  good  and  convenient  laboratory  should  be  described, 
with  all  its  requisites  and  accompaniments,  the  whole  being 
adapted  according  to  the  convenience  of  the  person  who  may 
for  the  first  time  be  forming  his  chemical  establishment. 

4.  If  equally  convenient,  it  is  generally  better  that  the  room 
to  be  converted  into  or  built  for  a  laboratory,  should  be  on 
the  ground  of  basement  floor,  as  water  is  then  easily  laid  on, 
the  foul  water  from  the  sink  can  be  readily  conveyed  away, 
and  coal,  carboys,  and  other  dusty  and  heavy  articles  more 
conveniently  carried  into  it.     The  size,  as  has  been  before 
intimated,  may  vary  very  much;  but  a  room  of  from  20  to  24 
feet  by  16  or  IS  feet,  will  well  answer  the  purpose.     Where, 
however,  it  is  otherwise  unimportant,  the  size  of  a  laboratory 
intended  to.be  actively  used  shoujd  be  as  large  as  possible; 
otherwise,  when  chemical  apparatus  accumulates,  and  several 
sets  of  experiments  are  in  progress  at  once,  it  may  be  found 
that  confusion  and  error  arise  solely  from  the  want  of  room.* 

*  The  prefixed  view  of  Dr  Hare's  laboratory  is  given  to  show  the  best  model 
in  this  country  of  a  laboratory  attached  to  a  public  institution.— ED. 


THE  LABORATORY FLUES.  19 

5.  If  the  place  is  to  be  built  for  the  purpose,  then  no  diffi- 
culty will  arise  in  the  construction  and  arrangement  of  the 
flues  and  lights  ;  which,  though  of  great  importance,  cannot 
usually  be    introduced   or  altered   easily  in  a  room   already 
finished.     Where  the  opportunity  occurs,  the  place  should  be 
furnished  with  several  flues,  and  an  advantage  isgained  if  their 
terminations  in  the  room  are  separated  a  little  distance  from 
each  other.  Sometimes  it  is  easy  to  spread  these  over  one  side 
or  wall  of  the  room,  the  stack  in  which  they  unite  being  carried 
up  immediately  in  their  neighbourhood*     One  flue  is  essen- 
tially necessary  for  the  draught  of  that  furnace  which  will  be 
lighted  daily  for  ordinary  operations,  and  the  ventilation  and 
warming  of  the  place.     Another  is  in  many  cases  essen- 
tially requisite  for  the  construction  of  a  wind  furnace ;  ano- 
ther or  two  are  desirable  to  serve  as  vents  for  the  convey- 
ance of  fumes,  or  occasionally  to  be  connected  with  mov- 
able furnaces.     The  lower  extremity  of  each   is  generally 
best  terminated  by  a  stone  in  the  wall  having  a  round  aper- 
ture :  when  out  of  use,  this  is  to  be  closed  by  a  stopper ; 
when  in  service,  the  stopper  is  to  be  withdrawn,  and  the  flue 
continued  by  a  piece  of  funnel  pipe  fitted  loosely  into  the 
hole;  the  pipe  being  continued  to  the  furnace  in  operation, 
or  otherwise  terminated,  according  to  the  use  to  which  the 
flue  is  to  be  put.     All  of  them  should  have  dampers,  that 
perfect  government  of  the  draught  may  be  obtained.     If  but 
one  flue  can  be  had,  it  must  be  turned  to  account  in  the  best 
way  possible,  either  by  making  it  divide  and  terminate  below 
in  two  or  three  places,  using  brickwork  or  funnel  pipe  for 
this  purpose,  as  maybe  convenient;  or  by  supplying  the 
place  of  furnaces  and  apparatus  requiring   flues,  by  such 
substitutes  as  will  allow  of  their  being  dispensed  with,  in 
the  manner  hereafter  to  be  described.     When  necessary,  a 
brick  flue  may  be  altogether  omitted,  and  its  place  supplied 
by  funnel-pipe,  but  this  arrangement  is  almost  always  un- 
comfortable and  inconvenient. 

6.  It  is  generally  a  matter  of  indifference,  or  at  least  of 
taste,  whether  a  laboratory  have  skylights  or  windows,  but  it 
is  always  an  advantage  to  have  it  well  lighted.     Skylights 
throw  the  light  very  agreeably  over  sand-baths  and  furnaces, 


22  THE  LABORATORY FILTERING  STANDS. 

situation  is  generally  against  the  fire-place, .  and  the  flue  of 
the  furnace  is  then  easily  connected  wuh  the  chimney  pre- 
viously existing. 

10.  When  a  furnace  of  this  kind  stands  against  the  wall, 
it  is  frequently  advantageous  to  construct  a  wooden  hood 
over  the  sand-bath,  to  receive  and  conduct  away  the  fumes 
evolved  during  the  digestions  and  solutions  made  upon  it. 
An  extensive  hood,  however,  requires  a  separate  flue,  or  it 
will  injure  the  draught  of  the  fire  ;  and  if  the  furnace  be  in 
the  middle  of  the  laboratory,  a  fixed  hood  of  any  kind  inter- 
feres with  its  convenient  use.     It  is  generally  better  in  these 
cases  to  adopt  the  temporary  hood  and  contrivances  which 
will  be  described  hereafter  (392).     A  particular  description 
of  the  construction  of  the  furnace  itself  will  also  be  given 
under  the  head  of  furnaces  (169). 

11.  The  tables  are  most  important  parts  of  laboratory  fur- 
niture ;  they  should  be  as  extensive  as  the  room  will  admit 
of,  and  be  so  placed  as  to  allow  of  ready  access;  hence  a 
large   one  or  two  placed  towards  the  middle  of  the  room, 
and  in  such  a  situation  as  to  be  well  lighted,  are  very  useful. 
They  should  be  made  strong,  and  be  furnished  with  draw- 
ers, unless  indeed  one  be  closed  in  by  doors,  so  as  to  form 
cupboards  having   shelves   within   to  hold  rough  articles ; 
and  if  such  a  one  could  have  a  situation  given  it  near  the 
sink,  as  a  kind  of  cleansing  and  washing  table,  its  advan- 
tage would  soon  be  experienced.     The  table  appropriated 
to  testing  operations  and  experiments  with  corrosive  fluids, 
as  acids  and  alkalies,  is  sometimes  covered  with  lead,  or  even 
with  earthenware,  glazed  tiles  being  very  convenient  for  the 
latter  purpose,  but  a  hard  or  heavy  substance  endangers  the 
safety  of  thin  glass  vessels  when  laid  down  upon  it. 

12.  There  are  some  things  which  necessarily  have  their 
appropriate  and  constant  place  on  the  tables.     The  filtering 
stands  (528)  are  of  this  kind,  and  are  thus  raised  to  a  con- 
venient height  for  operations :  they  should  have  a  situation 
chosen  for  them,   which,  though  convenient  for  use  and 
close  to  that  part  of  the  table  to  be  kept  clear  for  general 
purposes,  should  not  be  in  the  way  of  the  operations  con- 
stantly going  on   there.     A  drawer  or  other  dry  place  in 


THE  LABORATORY SINK CUPBOARDS.         23 

the  immediate  neighbourhood  of  these  stands  should  be  ap- 
propriated to  filtering  paper.  The  mercurial  trough  (736) 
is  another  apparatus  which  should  have  its  assigned  place 
upon  the  tables;  and  the  particular  table  upon  which  it 
stands,  or  upon  which  mercurial  operations  are  generally 
performed  (144),  should  have  a  groove  cut  round  it  near  the 
edge,  with  a  hole  in  one  place  for  the  facility  of  collecting 
the  scattered  mercury.  Any  of  the  metal  which  may  be 
spilled  is  swept  or  wiped  into  the  groove,  and  thence  into  a 
hole,  and  thus  collected  and  preserved. 

13.  A  sink,  with  an  abundant  supply  of  water,  is  very  im- 
portant; and  although  it  is  just  possible  that  a  jug,  with  alarge 
leaden  funnel  and  a  pan  beneath,  may  suffice,  yet  so  advan- 
tageous is  the  unlimited  use  of  water  and  a  regular  sink  with 
its  drain,  that  much  should  be  done  to  secure  them.  The 
water  should  be  laid  on  from  a  cistern  that  contains  a  never- 
failing  supply,  and  the  sink  should  be  made  of  strong  wood- 
work lined  with  lead  ;  for  though  that  metal  is  liable  to  the 
action  of  mercury  and  some  metallic  solutions,  yet  on  the 
whole  it  is  less  subject  to  chemical  actiqn  than  any  other 
substance  ordinarily  placed  in  a  similar  situation.  The  sink 
should  be  made  as  large  as  convenient,  not  exceeding  30 
inches  by  42,  and^should  have  a  drain  which  will  freely  carry 
off  all  the  slops  and  water  which  are  likely  to  be  thrown 
down.  An  iron  stink-trap  should  be  placed  at  the  com- 
mencement of  the  drain,  not  merely  for  the  purpose  of  pre- 
venting unpleasant  smells,  but  for  the  retention  of  the  mer- 
cury gradually  washed  down,  which  in  an  active  laboratory 
of  research  amounts  to  no  small  quantity  in  two  or  three 
years.  A  sink  is  useful  not  only  for  washing  bottles,  glasses, 
jars,  &c.,  but  for  many  chemical  operations,  such  as  filling 
airholders,  washing  minerals,  preparing  gluten,  distillation, 
&c.,  and  should  be  made  convenient  for  all  these  purposes. 
It  will  of  course  be  placed  in  a  corner,  and  as  much  out  of 
the  way  as  is  consistent  with  its  free  use  ;  a  place  in  the  im- 
mediate neighbourhood  being  appropriated  to  its  cleansing 
accompaniments,  pails,  pans,  brushes,  brooms,  &c. 

14.   Cupboards  are   so   useful,  that  one,  or,  if  possible, 
more,  with  shelves  inside,  ought  to  be  provided,    'In  these 


24         THE  LABORATORY — SHELVES RETORTS. 

are  to  be  kept  clean  test-glasses,  jars,  measures,  retorts, 
flasks,  receivers,  &c.,  for  here  they  are  preserved  from  the 
dust  and  dirt  which  are  constantly  moving  and  settling  in 
the  laboratory  itself.  The  shelves  should  be  placed  at  dif- 
ferent intervals,  so  as  to  receive  glasses  of  various  sizes;  and 
one  or  two  of  them  should  have  a  number  of  round  holes 
cut  out,  from  an  inch  to  four  inches  in  diameter,  to  receive 
the  necks  of  retorts,  flasks  and  receivers.  Between  the 
shelves  should  be  fixed  various  hooks  and  nails  to  hold  and 
retain  tube  apparatus,  such  as  siphons,  detonating  tubes, 
tubes  of  safety,  &c.  One  cupboard-shelf  should  be  par- 
ticularly appropriated  to  receive  products  of  experiments  in 
progress  which  have  to  be  preserved  for  a  few  days  (1302) ; 
or  things  which,  being  valuable,  are  but  rarely  required,  as 
potassium,  ,&c. 

15.  All  parts  of  the  walls  of  a  laboratory  within  reach, 
conveniently  situated,  and  not  otherwise  occupied,  should  be 
fitted  up  with  shelves  in  a  firm  manner,  to  receive  bottles  and 
jars.  These  must  vary  in  strength,  size,  and  interval,  ac- 
cording to  their  intended  uses  ;  such  as  are  to  hold  the  bot- 
tles, containing  the  usually  extensive  and  continually  accu- 
mulating series  of  chemicajg,  need  seldom  be  of  greater 
height  or  depth  than  to  receive  a  six  or  eight  ounce  phial 
standing  close  against  the  wall.  Those  intended  for  the  jars 
of  the  pneumatic  trough  must  be  wider  and  at  greater  inter- 
vals; and  those,  again,  which  are  intended  to  hold  the  stock- 
bottles  must  be  considerably  stronger,  inconsequence  of  the 
weight  to  be  borne  by  them.  In  arranging  the  shelves,  it 
will  be  proper  to  pay  attention  to  their  situation ;  the  first 
series,  for  instance,  containing  the  chemicals  and  tests  in 
constant  use,  should  be  near  the  table  upon  which  operations 
are  most  generally  carried  on,  whilst  the  stock-bottles  may 
be  put  upon  shelves  considerably  out  of  the  way.  A  shelf 
near  the  sink,  with  holes  in  it,  upon  which  apparatus  which 
has  been  washed  and  rinsed  may  be  placed  to  drain,  is  very 
useful ;  and  two  or  three  others  in  the  same  neighbourhood, 
or  somewhere  out  of  the  way,  supply  places  for  chemical 
lamps,  oil-cans,  and  other  dirty  articles  that  cannot  but  exist 
in  a  laboratory. 


THE  LABORATORY— PLACES  OF  BLOCKS,  ETC.       25 

16.  Retorts  are   very  conveniently    preserved    by    being 
hung  on  wire  rings  from  an  inch  to  an  inch  and  a  half  or  two 
inches    in  diameter.     These  are  easily  made  out  of  copper 
wire,  and  being  screwed  or  fastened  in  a  row  into  a  wooden 
partition,  receive  the  necks  of  the  retorts,  and  hold  them  in  a 
very  safe,  compact,  and  convenient  manner.     The  advantage 
is  obtained,  also,    of  seeing  the   whole  stock  of  retorts  at 
once,  and  instantly  choosing  that  best  fitted  for  any  required 
purpose. 

17.  Analogous  in  its  office  to  the  shelves  is  the  tube-rack  ; 
it  is  intended  to  hold  pieces  of  glass  tube  from  one  to  four 
feet  long,  and  generally  consists  of  a  shelf  about  three  feet 
long  and  from  six  to  eight  inches  wide,  having  a  piece  fast- 
ened on  the  front  so  as  to  form  a  raised  edge  about  an  inch 
high  :  or  it  might  be  made  with  some  advantage  by  driving 
three  or  four  long  pins  or  holdfasts  into  the  wall  in  aline,  the 
end  of  each  being  turned  up.     No  wooden  bottom  is  in  this 
case  used,   and   the    piece  of  glass  tube  required  is  more 
readily  selected  from  among  the  rest,  than  when  upon  a  rack 
of  the  former  kind  ;  the  smaller  pieces  are,  however,  apt  to 
fall  through. 

1-8.  A  part  of  the  wall  should  be  selected  to  be  furnished 
with  long  spikes,  either  by  driving  them  into  the  brickwork, 
or  fastening  up  a  board  to  which  they  are  attached.  These 
serve  to  hold  retort  and  flask  rings,  and  large  bent  tubes,  such 
as  siphons,  curved  pieces,  &c.;  smaller  spikes  will  answer  a 
similar  purpose  for  the  numerous  coils  and  pieces  of  wire  that 
are  continually  required. 

19.  One  or  two  large  wooden  blocks  will  be  found  useful 
in  a  laboratory;  they  may  serve  as  bases  on  which  to  place 
heavy  mortars,  and  one  of  them  will  form  a  good  support  for 
a  spike  or  anvil.     They  should  have  their  appointed  situa- 
tions on  the  floor. 

20.  A  set  of  ten  or  twelve  small  blocks  of  wood,  about  four 
inches  square  and  of  different  thicknesses  from  half  an  inch  to 
three  inches,  are  also  of  great  service  in  supporting  parts  of 
apparatus  at  different  heights. 

21.  Some  consideration  must  be  given  in  appointing  the 
places  of  the  various  pieces  of  apparatus  and  furniture  in  most 

D 


26          THE  LABORATORY- — COAL-BOX TOOLS. 

eommon  use  ;  and  their  relation  to  the  tables,  the  bottles,  and 
each  other,  must  be  taken  into  account.  The  pneumatic 
trough  (729)  is  in  constant  service,  and  must  not  therefore  be 
situated  in  a  dark  place,  or  far  from  the  centre  of  activity  : 
access  to  it  should  be  ready,  and  communication  from  other 
parts  open  and  free.  The  jar  shelves  (15)  should,  if  possi- 
ble, be  placed  near.  The  mercurial  trough  already  men- 
tioned as  standing  upon  the  the  table  (12)  should  be  similarly 
circumstanced.  The  table  blow-pipe  (242)  is  a  very  essen- 
tial article,  and  in  continual  use  :  it  should  have  a  place 
against  the  wall  near  to  its  appendage,  the  tube-rack. 
The  dirty,  but  useful  coal-box,  should  have  a  convenient, 
but  low  and  unobtrusive  situation  given  to  it,  that  it  may 
fully  perform  its  part  without  interfering  with  the  uses  or 
advantageous  situation  of  other  things.  It  can  hardly  be 
imagined  without  experience  how  much  is  gained  by  an  at- 
tention to  these  details  ;  for  though  an  operation  may,  either 
from  its  desultory  nature  or  its  subordinate  character,  be  of 
little  consequence  when  considered  separately,  yet  when  it 
has  to  be  repeated  again  and  again,  and  from  its  recurrence 
is  continually  entering  into  the  business  of  the  day,  it  attains 
a  degree  of  importance  which  makes  its  ready  and  accurate 
performance  of  the  greatest  consequence. 

22.  The  necessity  of  such  things  in  the  laboratory  as  flasks, 
retorts,  receivers,  bottles,  phials,  mortars,  &c.,  will  be  evident, 
but  any  information  respecting  them  will  be  most  advanta- 
geously given  hereafter.     They  are  better  supplied  as  they 
are  wanted,  rather  than  by  a  previous  order  ;  and  in  that  way 
the  accumulation  of  what  is  unnecessary,  is  to  a  great  extent 
avoided. 

23.  But  there  are  other  things,  properly  denominated  tools, 
which,  being  always  useful,  should  be  immediately  procured. 
Amongst  these,  an  anvil  or  spike,  with  its  foot-block,  should 
stand  on  the  ground,  and  a  vice  should  be  fixed  against  one  of 
the  tables.     Two  or  three  hammers,  including  one  intended 
for  mineralogical  purposes,  some  cold  chisels,  a  screw-driver, 
a  saw,  cutting  chisels,  gimlets,  brad-awls;  half-round,  flat, 
and   small  three-square  files  ;  half-round,   flat  and  rat-tail 
rasps  ;  pincers,  pliers,  forceps,  a  trowel,  a  soldering-iron  with 


THE  LABORATORY MATERIALS — DRAWERS.         27 

its  appendages,  are  the  tools  which,  with  a  glue-pot,  and  a 
collection  of  nails  and  screws,  will  be  found  necessary  :  and 
to  these  may  be  added  a  saw-knife  for  cutting  soft  brick; 
coarse  spatulas,  either  of  wood  or  bone,  or  made  from  iron 
hoop ;  and  a  cork-screw. 

24.  There  are  several  articles  which  may  be  considered  as 
materials  in  a  laboratory.     Bricks  are  often  wanted  to  build 
up  temporary  furnaces,  or  to  form  supports  :  mortar  is  con- 
sequently useful ;  river-sand  is  required  for  sand-baths  and 
other  purposes,  and  is  readily  obtained  from  the  bricklayer. 
Corks  are  useful  in  a  thousand  ways  (1331),  and  should  be 
provided  of  good  quality,  and  of  all  sizes,  from  a  large  bung 
downwards  :  old  cards  are  extremely  convenient.     Matches 
string  and  bladder,  are  necessary. 

25.  Many  of  these  useful  articles  are  best  preserved  in 
drawers,  and  hence  the  necessity  of  a  number  of  these  re- 
ceptacles   in    a    laboratory.     If  the  tables  do  not  supply 
enough  of  them,  it  will  be  desirable  to  have  a  strong  rough 
set  exclusively  for  these  purposes.     The  appropriation  of 
drawers  requires  some  method  :  one  should  be  appointed 
to  receive  fragments   of  glass    tubes  too  small  to  remain 
in  the  tube-rack  ;   another  should  be  kept  exclusively  for 
the  reception  of  those  useful  laboratory  vessels,  glass  tubes 
of  various  sizes  closed  at  one  end  (910);    another,    from 
containing  corks,  will  be  the  cork-drawer;    another,    the 
tool-drawer ;   the  files  and  rasps,  however,  being,  from  their 
quantity  and  general  use,  worthy  of  a  drawer  to  themselves; 
the  round  glass  plates,  stirrers,  and  tapers,  used  in  the  labo- 
ratory, will  also  occupy  a  drawer ;    string,   with    bladder 
and  sand-paper,  another ;  and  tow,  with  dusters,  another ; 
drawers  being  the  most  convenient  places  for  these  things. 
One  drawer  should  be  divided  within  into  various  compart- 
ments intended  for  different  small  apparatus,  as  blow-pipes, 
forceps,  a  scratching  diamond,  platina  foil  and  wire,  &c. 

Besides  drawers,  a  few  small  strong  wooden  boxes  are 
convenient  in  a  laboratory,  for  containing  lime,  lute,  man- 
ganese, sand,  &c.;  and  a  few  wooden  trays,  with  low  rims, 
are  exceedingly  serviceable  for  removing  apparatus. 

26.  Distilled  water  must  be  included  among  the  chemist's 


28  THE    LABORATORY DISTILLED    WATER. 

requisites;  and  so  much  advantage  is  gained  by  its  abun- 
dant supply,  that  any  accessible  source  should  be  eagerly 
sought.  Distilled  water  in  large  quantities  is  by  no  means 
uncommon  in  towns,  for  in  consequence  of  the  numerous 
applications  of  steam,  the  opportunities  of  collecting  it 
are  frequent.  Wherever  steam  is  used  for  the  conveyance 
of  heat  through  pipes,  the  condensed  water  may,  with  a 
very  little  contrivance,  be  collected  in  abundance,  by  placing 
a  clean  cask  or  vessel  under  the  place  where  it  issues  forth. 
Such  water  must  of  course  be  tested  to  prove  its  purity; 
that  being  rejected  for  laboratory  use,  which  from  any  de- 
rangement in  the  pipes  or  other  circumstance  is  found  to 
be  impure.  Where  the  laboratory  cannot  be  supplied  in 
this  way,  the  water  must  either  be  bought  or  distilled 
(424);  the  furnace  before  described  (8.177)  is  extremely 
well  adapted  for  the  application  of  a  still  for  this  purpose. 
Distilled  water  is  best  preserved  for  table  use  in  a  bottle 
holding  about  a  quart,'  or  three  pints,  which  should  be 
quite  distinct  in  its  form  or  appearance  from  any  other 
bottle  in  the  laboratory,  so  that  no  mistake  respecting  it 
may  at  any  time  arise. 

27.  A  flint  and  steel,  with  matches,  or,  what  is  far  better, 
an  eupyrion,  should  always  be  conveniently  placed  in  the 
laboratory,  and  near  to  it  a  candle  and  candlestick.  The 
little  apparatus  called  Hertner's  Eupyrion  is  now  so  well 
known  in  most  towns,  that  no  difficulty  will  exist  in  ob- 
taining it.  To  those  who  do  not  know  the  instrument,  it 
may  be  as  well  to  observe,  that  it  consists  of  a  very  small 
bottle  half  filled  with  asbestus,  rather  closely  pressed,  and 
moistened  with  very  concentrated  sulphuric  acid,  the  quan- 
tity being  such,  that  though  it  thoroughly  wets  the  asbestus, 
it  cannot  flow  amongst  it  or  upon  the  sides  of  the  bottle  ; 
the  bottle  is  closed  by  a  good  tight  cork,  and  should 
never  be  opened  except  when  a  match  is  to  be  introduced, 
and  immediately  the  latter  is  withdrawn,  it  should  be  closed 
again.  The  matches  are  small  slips  of  wood  tipped  with 
sulphur  in  the  usual  way,  but  they  are  then  again  tipped 
over  the  sulphur  by  being  dipped  for  the  eighth  of  an  inch 
into  a  mixture  of  three  parts,  by  weight,  of  chlorate  of 


THE  LABORATORY APPARATUS-ROOM,  ETC.       29 

potash,  and  two  parts  of  starch  or  sugar,  mixed  with  a  little 
vermilion  to  give  it  colour,  and  water  enough  to  make  it 
into  a  thin  paste  :  this  is  allowed  to  dry  thoroughly.  One 
of  these  matches  suddenly  dipped  into  the  bottle,  so  as 
to  touch  the  sulphuric  acid,  and  snatched  out  again,  will 
immediately  inflame.  For  the  eupyrion  may  be  substituted 
the  phosphorus  bottle,*  made  by  stirring  a  piece  of  phos- 
phorus about  in  a  dry  bottle  with  a  hot  wire;  the  phosphorus 
undergoes  partial  combustion,  and  forms  a  highly  combus- 
tible coat  over  the  interior  :  a  common  sulphur  match  rub- 
bed against  the  inside  of  the  bottle  and  drawn  out  into  the 
air,  immediately  inflames  ;  or  if  it  should  not  do  so,  a  second 
stir  with  the  hot  wire,  or  two  or  three  days  rest,  will  ge- 
nerally render  the  bottle  a  good  one.  It  should  be  closed 
by  a  glass  stopper  so  as  to  prevent  access  of  air,  except  at 
the  short  momentary  intervals  when  it  is  in  use.  Both  this 
and  the  eupyrion  are  to  be  preferred  to  flint  and  steel. 

28.  There  remains  little  besides  to  perfect  the  preliminary 
furniture  of  a   laboratory.      A   blank   writing-paper  book 
should  be  upon  the  table,  with  pen  and  ink,  to  enter  imme- 
diately the  notes  of  experiments  (1290).     A  chair  may  be 
admitted,  and  one  will  be  found  quite  sufficient  for  all  ne- 
cessary purposes,  for  a  laboratory  is  no  place  for  persons 
who  are  not  engaged  in  the  operations  going  on  there. 

29.  Having  thus  described  the  laboratory,  it  will  easily  be 
understood,  that  great  advantages  would  arise  from  the  asso- 
ciation of  another  room  or  two  with  it,  which,  nevertheless, 
may  be  dispensed  with.     A  good  balance  is  a  very  delicate 
piece  of  apparatus,  and  is  soon  injured  and  deranged  if  ex- 
posed to  the  attacks  of  the  damp  and  corrosive  vapours  that 
are7  continually  floating  about  in  the  laboratory,  in  which  it 
should  therefore  be  allowed  to  remain  as  little  as  possible, 
and  yet  from  its  constant  use  should  not  be  far  removed.    If 
there  be  a  small  dry  room  at  hand,  it  will  be  very  convenient 

*  Wide  bottles,  rather  shorter  than  a  common  match,  and  having  a  small 
orifice,  are  best  suited  to  the  purpose  mentioned.  A  cork  is  preferable  to  a 
glass  stopper.  The  bottle  after  being  prepared  should  not  be  laid  on  its 
side. — ED. 


30  THE    LABORATORY,    ECT. 

generally  to  keep  the  balance  in  it;  and  there  the  air-pump 
and  its  receivers,  the  electrical  machine,  Leyden  jar,  and 
a  quantity  of  delicate  apparatus,  will  usually  be  its  com- 
panions. 

30.  On  the  other  hand,  such  things  as  lute,  sand,  charcoal, 
coke,  bricks,  crucibles,  voltaic  troughs,  carboys,  &c.,  do  not 
requirea  dry  place,  and  would  even  cause  injury  if  retained  in 
the  same  room  with  the  balance;  yet  it  is  advantageous,  if 
otherwise  convenient,  to  remove  them  from  the  laboratory 
into  a  separate  place,  that  the  former  may  be  left  unembar- 
rassed and  clear  for  operations.     These,  therefore,  would  go 
very  properly  into  a  dry  cellar  or  covered  shed,  or  any  place 
that  would  suit  as  a  rough  lumber-room.     Still  it  may  be  ob- 
served, that  these  places  are  not  essential ;  and  where  the 
laboratory  establishment  is  but  small,  all  the  delicate  appara- 
tus may  be  put  into  a  dry  cupboard,  and  the  other  things  find 
their  situation  in  the  laboratory  itself. 

31.  If  the  want  of  time,  or  if  other  circumstances,. should 
necessarily  limit  the  chemical  pursuits,  the  author  would  ad- 
vise a  person  so  situated  to  begin  by  providing  a  spirit-lamp, 
a  blow-pipe,  a  pair  of  pliers,  some  platina  foil  and  wire,  a 
platina  capsule,  a  few  Florence  flasks,  a  chemical  lamp,  a 
few  evaporating  basins,  a  few  pieces  of  quill  glass  tube,  and 
two  or  three  dozen  bottles  ;  with  some  of  the  most  useful 
chemicals,  as  the  acids  and  alkalies,  and  six  or  eight  of  the 
most  important  tests ;  and  to  purchase  all  other  things  as  the 
necessity  for  them  may  arise. 


SECTION.  II. 
BALANCE,  WEIGHING,  &c. 

32.  ON  entering  upon  a  part  of  this  work  which  relates 
more  directly  to  manipulation  than  the  matter  of  the  preceding 
pages,  it  may  be  proper  to  state  very  distinctly,  that  the  object 
is  not  to  give  information  relative  to  the  nature  or  construe- 


DELICATE    AND    COMMON    BALANCES.  31 

tion  of  chemical  apparatus  in  general,  but  to  teach  its  sim- 
plest, most  effectual,  and  accurate  use.  It  will  be  the  endea- 
vour of  the  author  to  keep  all  in  strict  subordination  to  this 
object ;  and  when  he  enters  into  the  construction  and  prin- 
ciplesof  aninstrument,it  will  be  solely  with  a  view  to  the  clear 
comprehension  of  the  manner  of  using  it.  Hence  a  reason  for 
the  apparent  disproportion  which  will  now  and  then  appear 
in  the  details  of  this  subordinate  and  descriptive  part:  for 
whatever  the  pupil  or  chemist  can  himself  do  towards  the  cor- 
rection or  construction  of  an  instrument,  will  be  fully  de- 
scribed, whilst  that  which  must,  of  necessity,  be  done  by 
the  workman,  will  be  passed  over  in  silence.  To  teach  a 
person  how  to  make  a  balance,  or  to  inform  him  how  it  is 
made,  is  not  the  object  of  the  writer  ;  whilst,  on  the  contrary, 
its  use  is  the  very  point  in  view  :  whatever,  therefore,  facili- 
tates the  latter,  or  whatever  can  be  done  to  correct  slight 
derangement,  by  one  who  is  not  a  workman,  ought  now  to 
claim  our  attention. 

33.  A  chemist  cannot  do  without  a  delicate  balance ;  it 
is  absolutely  necessary  to  his  repetition  of  the  most  impor- 
tant experiments  of  others,  or  to  his  own  independent  pro- 
gress. If  he  be  an  active  operator,  he  will  require  two  or 
three  balances  ;  for  the  weights  with  which  it  is  necessary  to 
work  are  almost  without  limit,  and  cannot  be  estimated  by 
the  same  instrument.  Large  quantities,  if  weighed  in  bal- 
ances competent  to  show  minute  differences  in  small  weights, 
would,  by  flexure  of  the  beam  or  change  in  the  points  of 
support,  infallibly  injure  or  even  destroy  them  ;  and  small 
weights  cannot  be  appreciated  in  instruments  intended  for 
great  quantities;  because  of  the  strength  it  is  necessary  the 
latter  should  have,  and  the  consequent  weight  and  compar- 
ative roughness  of  the  parts.  One  pair  of  scales  should 
therefore  be  provided  that  will  weigh  from  one  ounce  up  to 
three  or  four  pounds,  or  even  more,  and  be  so  constructed  as  to 
turn  with  two  or  three  grains,  when  loaded  with  their  great- 
est weight.  They  can,  when  required,  be  made  very  deli- 
cate and  correct,  but,  except  in  particular  cases,  that  is  not 
necessary.  Another  pair  of  scales,  calculated  to  weigh  from 
half  a  grain  to  two  or  three  ounces,  with  considerable  accu- 


32  COMMON  BALANCES WEIGHTS. 

racy,  and  turning  with  about  one  half  or  one  third  of  a  grain 
when  fully  loaded,  should  be  kept  for  laboratory  purposes. 
These  are  intended  for  common  use;  and  as  it  is  a  great 
object  to  save  the  superior  instrument  from  the  injury  occa- 
sioned by  too  frequent  use,  and  to  preserve  it  from  exposure 
to  the  vapours  which  are  constantly  escaping  in  the  pro- 
gress of  operations,  or  from  the  bottles,  should  be  substituted 
as  often  as  possible  in  the  latter ,  especially  in  cases  which 
require  the  balance  for  the  laboratory.  The  choice  instru- 
ment should  be  sufficiently  delicate  to  weigh  from  600  to 
1000  grains  and  downwards,  indicating  distinctly  and  cer- 
tainly differences  equal  to  the  y^^y  or  Y^O"OT  Part  of  the 
weight  in  the  scale. 

34.  The  materials  and  construction  of  balances  vary  so 
much,  as  also  do  the  circumstances  which  influence  their 
purchase,  that  no  general  directions  on  this  point  can  be 
well  given.  Whether  large  or  small,  they  are  best  on  fixed 
supports,  and  not  suspended  loosely,  although  very  good 
ones  of  the  latter  construction  are  made.  They  should  be 
preserved  from  all  damp  and  vapours  ;  and  the  beam  of  the 
large  one,  if  its  construction  will  admit  of  it,  and  even  the 
next  pair,  frequently  oiled  and  wiped.  The  more  delicate 
instruments  should  be  cleaned  by  the  maker  :  much  harm  is 
sometimes  produced  by  rough  and  hasty  cleansing ;  and  if, 
when  about  to  be  used,  it  is  seen  that  a  spot  arising  from 
rust,  or  corrosion,  or  any  other  cause,  exist  on  the  beam  or 
pan  of  a  delicate  balance,  it  is  better  to  compensute  for  the 
difference  of  weight  it  occasions,  by  adding  a  temporary 
counterpoise  to  the  pans,  than  to  try  to  remove  it  previous 
to  the  operation.  If  the  balances  are  so  constructed  as  to 
pack  into  boxes  or  cases,  they  should  be  kept  in  such  cases 
when  not  in  use.  Delicate  instruments  are  always  inclosed 
in  cases,  and  are  so  fixed  in  them  as  to  require  and  admit  of 
their  use  without  removal.  When  not  in  use,  the  cases 
should  always  be  closed.  A  loose  green  baise  or  linen  bag 
to  throw  over  the  balances  when  in  the  laboratory,  and  not 
in  use,  is  serviceable,  and  whenever  of  necessity  the  delicate 
balance  is  brought  into  the  laboratory,  it  should  be  returned 
to  its  proper  situation  immediately  that  it  is  done  with. 


COMMON    BALANCES WEIGHTS.  33 

The  implement  itself  is  so  expensive,  so  soon  suffers  injury, 
and  then  has  its  value  and  use  so  rapidly  diminished,  that 
every  care  should  be  taken  to  preserve  it  in  efficient  order. 

35.  The  weights  for  these  balances  are  as  various  as  the 
instruments  themselves.     They  will  be  wanted   from   3  Ibs. 
down  to  the  hundredths  of  a  grain,  and  will  form   at  least 
two  sets,  the  one  consisting  of  avoirdupois  pounds,  ounces, 
and  drachms,  and  the  other  of  grains,   from  1000  down  to 
the  minutest  fractions. 

36.  These  weights  are  sometimes  made  of  brass ;    the 
smaller  ones,  however,  are  commonly  of  platinum.  The  frac- 
tions of  a  grain  should  always  be  of  platinum,  and  it  would  be 
much  better  if  that  metal  were  constantly  used,  for  weights 
not  surpassing  10  grains.     Perhaps   its  expense  for  heavier 
weights    would    sometimes    be    objectionable,   but   this    is 
fully  compensated  by  the  unchangeableness  of  the  weights 
either  from  oxidation  or  corrosion,   and  the   facility  with 
which  they  are  cleaned  from  ordinary  dirt,  either  by  slight 
wiping  or  momentary  exposure   to    the    flame  of  a  spirit- 
lamp.     Where  expense  is  no  object  all  the  weights  should 
be  of  platinum  ;  their  permanent  correctness  compensating 
abundantly  for  the  increased  cost. 

37.  If  platinum  be  not  used,  there  is  probably  no  common 
metal  better  than  brass,  of  which  to  construct  weights ;  the 
larger  grain  weights,  and  also  the  pound  series  and  its  divi- 
sions, may  be  made  of  this  alloy.     It  is  liable  to  be  affected 
very  materially  by  the  laboratory  fumes,  and  in  consequence 
small  weights  constructed  of  it  are  often  rendered  useless  in  a 
very  short  period.    Keeping  them  in  a  close  box  retards  this 
kind  of  injury.     The  pound  and  ounce  weights  are  frequently 
constructed  in  sets,  each,  weight  being  hollow,  having  the 
form  of  a  truncated  cone,  and  fitting  into  the  others,  so  as 
when  arranged  together  to  form  a  solid  mass.     Such  weights 
are   very  convenient  in   arranging  counterpoises,  the  cup 
form  enabling  the  largest  weights  used   to  receive  all  the 
additional  matter  required  to  make  the  counterpoise  accu- 
rate as  will  be  seen  in  the  practice  to  be  described  hereaf- 
ter (64). 

E 


34  WEIGHT  BOX ITS  ACCOMPANIMENTS. 

38.  The  laboratory  box  of  grain  weights  should  include  a 
pair  of  small  brass  pincers  or  forceps,  for  the  divisions  of  a 
grain  (54).     The  latter  are  too  minute  to  be  moved  expe- 
ditiously  and  safely   by  the  hand  ;  and  unless  the  weights 
be  comparatively   large,  the  handling  of  any  of  them  is  li- 
able to  communicate  extraneous  matter,  and  thus  render 
them  more  or  less  inaccurate. 

39.  Associated  with  the  weights  should  be   some  con- 
venient substance  for  the  purpose  of  counterpoising  cruci- 
bles, capsules,  tubes,  &c.  (64).     A  little  box  of  clean  shot  of 
different  sizes  mixed  together  answers  this  purpose  in  part 
very  well ;  and   its  contents  may  be  completed   by  a  few 
pieces  of  sheet  lead  or  tin  foil. 

40.  The  balance  and  weights  should  be  carefully  exam- 
ined at  intervals,  to  ascertain  their  accuracy,  for  if  they  in- 
volve unnoticed  errors,  the  experiments  made  with  them  may 
be  worse  than  useless.     Some  curious  conclusions,  tending 
to  subvert  most  important  chemical  truths,  might  be  quoted 
as  having  arisen  solely  in  this  way. 

41.  The  theory  of  the  balance  is  so  simple,  that  the  tests 
of  its  accuracy  will  be  easily  understood,  and  as  easily  prac- 
tised *.     It   may  be  considered  as    an   uniform   inflexible 
lever,  supported  horizontally  at  the  centre  of  gravity,  and 
supporting  weights  at  equal  distances  from  the  centre,  by 
points  in  the  same  horizontal  line  with  the  centre  of  gravity. 
If  the  weights  be  equal,  the  one  will  counterpoise  the  other ; 
if  not,  the  heavier  will  preponderate.     In  the"  balance,  as 
usually  constructed,  there  are  certain  departures  from  the 
theory  as  above  expressed — some  from  the  impossibility  of 
execution,  and  others  in  consequence  of  their  practical  util- 
ity ;  and  a  good  balance  may  be  said  to  consist  essentially 
of  a  beam  made  as  light  as  is  consistent  with  that  inflexibil- 
ity which  it  ought  to  possess,  divided  into  two  arms  of  equal 
weight  and  length,  by  a  line  of  support  or  axis,  and  also  termi- 
nated at  the  end  of  each  arm  by  a  line  of  support  or  axis  in- 
tended to  sustain  the   pans.     These  three   lines  of  support 
should  be  exactly  parallel  to  each  other,  in  the  same  horizontal 
plane,  and  correctly  perpendicular  to  the  length  of  the  beam  ; 

*  See  Nicholson's  or  Ure's  Dictionary  of  Chemistry,  article  Balance. 


ACCURACY  OF  A  BALANCE  EXAMINED.          35 

and  the  plane  in  which  they  lie  should  be  raised  more  or  less 
above  the  centre  of  gravity  of  the  beam,  so  that  the  latter 
should  be  exactly  under  the  middle  line  of  suspension.  It 
will  be  unnecessary  in  this  place  to  speak  of  the  coarse  faults 
which  occur  in  the  ordinary  scales — these  will  easily  be  un- 
derstood ;  and  from  what  has  to  be  stated  of  the  examina- 
tion of  the  most  delicate  instrument,  the  impossibility  of 
avoiding  them  without  incurring  an  expense  inconsistent 
with  their  ordinary  use,  will  be  as  readily  comprehended. 

42.  It  will  be  easily  understood  that  a  beam  constructed 
with  knife  edges  resembles  the  one  before  mentioned  ;  and 
being  supported  on  horizontal  planes  by  the  central  line  of 
suspension,  as  is  generally  the  case,  will  take  a  horizontal 
position,  in  consequence  of  the  situation  of  the  centre  of 
gravity.  The  addition  of  the  pans  causes  no  change  in  this 
ultimate  position  of  the  beam,  because  they  are  of  equal 
weights.  The  delicacy  of  a  balance  depends  very  materi- 
ally upon  the  relative  situations  of  the  centre  of  gravity,  and 
the  lines  of  support,  i.  e.  the  middle  and  the  extreme  lines  of 
suspension.  If  the  centre  of  gravity  be  considerably  de- 
pressed below  the  fulcrum,  then,  upon  trying  the  oscillations 
of  the  balance  by  giving  it  a  little  motion,  they.will  be  found 
to  be  quick,  and  the  beam  will  soon  take  its  ultimate  state 
of  rest;  and  if  weights  be  added  to  one  side,  so  as  to  make 
it  vibrate,  or  turn  as  the  expression  is,  or  else  to  bring  it  to 
a  certain  permanent  state  of  inclination,  the  quantity  requir- 
ed will  be  found  to  be  comparatively  considerable.  As  the 
centre  of  gravity  is  raised,  the  oscillations  are  slower,  but 
producible  by  a  much  smaller  impulse,  the  beam  is  longer 
before  it  attains  a  state  of  rest,  and  it  turns  with  a  smaller 
quantity.  When  its  situation  coincides  with  the  fulcrum  or 
centre  of  oscillation,  that  also  being  in  the  plane  joining  the 
two  extreme  lines  of  suspension,  then  the  smallest  possible 
weight  will  turn  the  beam  (supposing  the  knife  edge  and 
suspending  plane  perfect),  the  oscillations  no  longer  exist, 
but  one  side  or  the  other  preponderates  with  the  slightest 
force;  and  the  valuable  indication  which  is  furnished  by  the 
extent  and  velocity  of  the  vibrations  is  lost.  The  case 
where  the  centre  of  gravity  is  above  the  fulcrum  rarely  if 


36          CIRCUMSTANCES    INFLUENCING    THE    INDICATIONS. 

ever  occurs ;  such  a  balance,  when  equally  weighted,  would 
set  on  the  one  side  or  the  other,  that  side  which  was  in  the 
slightest  degree  lowest  tending  to  descend  still  lower,  until 
obstructed  by  interposing  obstacles  ;  unless,  indeed,  the  ful- 
crum was  placed  considerably  above  the  line  joining  the  ex- 
treme points  of  suspension,  in  which  case  the  weights  in 
the  pans  might  counteract  the  effect  dependent  upon  the  ele- 
vation of  the  centre  of  gravity.  In  balances  intended  to 
carry  large  quantities,  it  is  necessary  to  place  the  centre  of 
gravity  lower  than  in  those  of  minute  quantities,  that  they 
may  vibrate  regularly  and  readily,  and  hence  one  cause  why 
they  are  inferior  in  ^delicacy,  for,  as  a  consequence  of  the 
arrangement,  they  will  not  turn  (or  indicate),  except  with  a 
larger  weight. 

43.  The  vibrations  of  a  balance  vary  with  the  quantity  of 
matter  with  which  it  is  loaded  ;  and  the  more  the  weight  in 
the  pans,  the  slower  their  occurrence.     These  should  be  ob- 
served, and  the  appearances  retained  in  the  mind,  in  con- 
sequence of  the  useful  indications  they  afford  in  operations 
of  weighing.     A  certain  extent  and  velocity  of  vibration 
would,  in  some  degree,  indicate  to  the  person  used  to  the  in- 
strument nearly  the  weight  required  to  produce  equilibrium ; 
but  the  same  extent  and  velocity,  with  a  weight  much  larger 
or  smaller,  would  not  be  occasioned  by  an  equal  deficiency 
or  redundancy  of  weight,  as  in  the  former  case.     The  weight 
required  also  to  effect  a  certain  inclination  of  the  beam,  or 
to  turn  it,  should  be  known,  both  when  it  is  slightly  and 
when  heavily  loaded.    If  the  instrument  turn  with  T£F  of  a 
grain  when  600  grains  are  in  each  scale,  or  with  TF^  of 
the  weight  to  be  estimated,  it  may  be  considered  as  very 
good. 

44.  Balances  are  sometimes  liable  to  set,  as  it  is  called, 
when  overloaded.     The  effect  consists  in  a  permanent  de- 
pression of  that  side  which  is  lowest :  thus,  if  a  balance  be 
equally  weighted  in   each   pan,   but  overloaded,  it  will,  if 
placed  exactly  horizontal,  remain  so;  but  the  slightest  im- 
pulse or  depression  on  one  side  destroys  the  equilibrium,  the 
lower  side  continues  to  descend  with  an  accelerated  force, 
and  ultimately  remains  down,  being,  to   all   appearance, 


EXAMINATION     OF    A    BALANCE.  37 

heavier  than  the  other.  Generally  speaking,  the  more  deli- 
cate a  balance,  the  sooner  this  effect  takes  place,  and  hence 
one  limit  to  the  weight  which  it  can  properly  carry.  This 
setting  of  the  balance,  and  the  general  diminution  of  deli- 
cacy by  increase  of  weight,  should  be  carefully  kept  in  mind. 
The  setting  is  considered  as  dependent  upon  the  position  of 
the  fulcrum,  below  the  line  which  joins  the  extreme  points 
of  suspension  of  the  beam;  the  effect  which  would  thus  be 
produced  being  masked  for  a  time  by  the  centre  of  gravity 
in  the  beam  falling  below  the  fulcrum. 

45.  When  the  beam,  freed  from  the  pans,  but  supported 
on  its  stand,  has  been  found  to  oscillate  regularly  and 
equably,  and  gradually  to  attain  a  horizontal  position  of  rest, 
it  should  be  reversed,  that  is,  taken  up  and  turned  half-way 
round,  so  as  to  make  that  arm  which  before  pointed  to 
the  right,  now  point  to  the  left.  The  beam  should  then  again 
be  made  to  oscillate;  and  if  it  performs  regularly,  as  before, 
finally  resting  in  a  horizontal  position,  it  has  stood  a  severe 
test,  and  promises  well.  The  faults,  which  are  likely  to  be 
disclosed  in  this  way,  depend  upon  imperfections  in  the 
work  of  the  middle  knife  edge  and  the  planes  upon  which 
it  rests.  The  edge  is  made  either  of  agate  or  steel,  and 
should  be  formed  out  of  one  piece  of  matter,  and  finished  at 
once ;  every  part  of  the  edge  being  ground  upon  the  same 
flat  surface  at  the  same  time.  In  this  way  the  existence  of 
the  two  extreme  or  bearing  parts  of  the  edge  in  one  line  is 
insured  ;  but  when  the  two  parts  which  bear  upon  the  planes 
are  formed  separately  upon  the  different  ends  of  a  piece  of 
agate  or  steel,  or,  what  is  worse,  when  they  are  formed  on 
separate  pieces,  and  then  fixed  one  on  each  side  the  beam,  it 
is  scarcely  possible  they  should  be  in  the  same  line,  and,  if 
not,  the  beam  cannot  be  correct.  These  knife  edges  usually 
rest  upon  planes,  or  else  in  curves.  The  planes  should  be 
perfectly  flat  and  horizontal,  and  exactly  at  the  same  height; 
the  curves  should  be  of  equal  height,  and  their  axis  in  the 
same  line.  If  they  are  so,  and  the  knife  edge  is  perfect, 
then  the  suspension  will  be  accurately  on  the  line  of  the 
edge,  and  reversing  the  beam  will  produce  no  change. 

46.  When  the  pans  are  hung  upon  the  beam,  the  balance 


38  EXAMINATION    OF    A   BALANCE. 

should  of  course  still  remain  horizontal.  The  lines  of  sus- 
pension for  the  pans  are  not  so  difficult  to  obtain  correctly  as 
that  before  spoken  of;  but  they  should  be  tried  by  changing 
the  pans,  then  by  reversing  the  beam,  and  afterwards  by 
changing  the  pans  again.  The  irregularities  which  may  in 
this  way  be  discovered  in  a  balance  can  be  corrected  only 
by  the  workman,  and  are  always  difficult  points  in  the  final 
adjustment.  Faults  may  exist  in  a  slight  degree  in  a  very 
excellent  instrument,  and  the  inaccuracies  which  might 
result  from  ignorance  of  them  may  be  avoided  when  they 
are  known,  by  attention  to  directions. 

47.  The  arms  should   in   length  and  weight  be  equal  to 
each  other  :  the  length  of  each   is  accurately  the  distance 
from  the  middle  to  the  distant  knife  edge,  all  the  edges 
being  considered  parallel  to  each  other,  and  in  the  same 
plane.       The    two    arms    should    accord   perfectly    in   this 
respect;  but  the  weight  is  by  no  means  necessarily  subject 
to  equality,  though  it  is  better  that  it  should  be  so.     One 
arm,  with  its  pan,  may  be  considerably  heavier  than  the 
other,  but  from  the  disposition  of  the  weight  in  the  lighter 
arm  towards  the  extremity,  or  in  the  heavier  towards  the 
middle  of  the  beam,  the  equilibrium  may  be  perfect;  and, 
therefore,  no  inaccuracy  be  caused  thereby  in  the  use  of  the 
balance.    Instruments  are  usually  sent  home  in  equilibrium, 
and  require  no  further  examination  as  to  this  particular  point 
than  to  ascertain  that  they  really  are  in  adjustment;  and 
that,  after  vibrating  freely,  they  take  a  horizontal  position. 
If  they  should  not  do  so,  the  fault  is  easily  corrected  for  the 
time  by  a  small  counterpoise. 

48.  Equality  in  the  length  of  the  arms  is  much  more  im- 
portant, and  may   be  ascertained   in    two    or   three  ways, 
Suppose  the  balance  with  its  pans  to  vibrate  freely  and  rest 
in  a  horizontal  position,  and  that  after  changing  the  pans 
from  one  end  to  the  other,  the  balance  again  takes  its  hori- 
zontal state  of  rest.     In  such  a  case  an  almost  certain  proof 
is  obtained  of  equality  in  the  length  of  the  arms.    They  may, 
however,  be  equal,  and  yet  this  change  of  the  pans  from  end 
to  end  may  occasion  a  disturbance  of  equilibrium,  because  of 
the  unequal  distribution  of  weight  in  the  beam   and  pans ; 


EXAMINATION    OF    THE    WEIGHTS.  39 

but,  to  insure  an  accurate  test,  restore  the  pans,  and  conse- 
quently the  equilibrium,  to  the  first  state  ;  put  equal,  or  at 
least  counterpoising  weights,  into  the  pans,  loading  the  ba- 
lance moderately,  and  then  change  the  weights  from  one  pan 
to  another,  and  again  observe  whether  the  equilibrium  is  re- 
tained ;  if  so,  the  lengths  of  the  arms  are  equal. 

Tests  of  this  kind  are  quite  sufficient  for  the  purpose  of  the 
chemist ;  who,  having  ascertained  that  his  balance,  whether 
slightly  or  fully  laden,  vibrates  freely, — turns  delicately, — 
has  not  its  indications  altered  by  reversing  the  beam  or 
changing  counterpoising  weights, — may  be  perfectly  satis- 
fied with  it,  and  leave  the  fuller  consideration  of  the  difficult 
points  and  corrections  to  the  instrument  maker. 

49.  The  weights  should  undergo  an  examination  as  well 
as  the  balance,  and  it  is  necessary  to  make  this  with  re- 
ference to  their  accuracy  when  new,  and  also  to  their  change 
by  wear  or  corrosion.  It  is  essential  in  the  first  place  to  set 
out  with  a  good  standard,  and  though  this  point  is  of  neces- 
sity generally  left  to  the  workman,  yet,  when  possible,  it  is 
very  desirable  that  the  1,  10,  100,  and  1000  grain  weight 
should  be  compared  with  others  of  good  authority.  The 
most  ready  method  of  detecting  errors  in  the  subdivisions, 
is  to  make  up  equal  quantities  from  different  weights,  and 
compare  them  together  in  the  balance,  a  large  one  being 
tried  against  eight  or  ten  smaller,  as  the  100  grain  weight 
against  those  of  40,  30,  10,  8,  5,  4,  2,  and  1 ;  and  then 
again,  from  a  quantity  made  up  of  several,  to  remove  some 
and  replace  them  by  others,  as  for  instance,  for  the  30 
grain  weight  above,  to  substitute  a  10  and  four  5  grain 
weights.  The  fractions  of  the  grain  should  be  examined 
in  the  same  manner,  and  if  any  material  error  exists,  it 
will  thus  readily  be  discovered.  Should  the  balance  in 
use  be  one  which,  from  accident  or  other  circumstances, 
is  affected  in  its  indications  by  changing  the  weights  in 
the  pans,  then,  in  these  trials,  all  the  changes  should  be 
made  in  one  pan  only,  the  weight  in  the  other  being  con- 
sidered as  a  mere  counterpoise,  and  left  undisturbed  from 
first  to  last.  The  trials  with  those  weights  which  accompany 


40  PROCESS    OF    WEIGHING. 

the  best  balance,  and  are  intended  exclusively  for  very  deli- 
cate experiments,  should  be  made  with  extreme  care. 

50.  The  examinations  which  are  to  take  place  at  different 
periods  to  ascertain  the  continued  correctness  of  the  weights, 
are  to  be  conducted  in  a  similar  manner,  except  indeed  when 
there  is  reason  to  suspect  the  alteration  of  a  particular 
weight,  which  will  then  of  course  be  tried  against  one  ad- 
mitted to  be  correct.     These  trials  should  be  more  or  less 
frequent,  according  to  the  exposure  of  the  weights ;  those, 
which   from   being  continually   in    the   laboratory  rapidly 
change  their  colour  and  appearance,  will  often  require  ex- 
amination ;  but  platinum  weights  are  in  this  respect  unal- 
terable, and  are  liable  to  very  little  derangement  of  any  kind 
from  ordinary  use. 

51.  The  operation  of  weighing   is   very  simple,  and  it 
is  only  because  in  the  hands  of  the  chemist  it  becomes  one  of 
extreme  delicacy  and  frequency,   that  the  facilities  for  its 
performance  require  to  be  mentioned.     It  should  in  the  first 
place  be  ascertained  before  every  operation,  that  the  balance 
is  in  order,  as  far  as  relates  to  its  perfect  equilibrium,  and  to 
the  freedom  of  vibration ;  and  also  that  no  currents  of  air 
are  passing  through  the  case,  so  as  to  affect  its  state  of  mo- 
tion or  rest ;  a  situation  being  chosen  where  such  influences 
may  be  avoided.     If  from  any  accidental  cause  it  be  not  in 
equilibrium,  it  should  be  balanced  by  a  fragment  of  paper, 
or  a  slip  of  tin  or  lead  foil.     If  its  vibrations  are  imperfect, 
and  impeded,  the  cause,  whatever  it  be,  must  be  discovered 
and  removed,  or  a  delicate  weighing  cannot  be  performed. 

52.  When  the  substance  to  be  weighed  consists  of  one  or 
a  few  pieces  only,  it  is  merely  necessary  to  put  it  into  one 
pan,  and  to  add  weights  to  the  other,  until  the  two  are  in 
equilibrium.     A  delicate  balance  is  always  furnished  with 
means  of  supporting  the  pans,  independently  of  the  beam ; 
and  the   beam  itself  is  also  supported  when  required,  by 
other  bearings  than  its  knife  edges ;  and  in  such  a  manner 
as  to  admit  of  the  rapid  removal  of  these  extra  supports,  that 
the  instrument  may  be  left  free  for  vibration.     This  is  done 
that  the  delicate  edges  of  suspension  may  not  be  injured,  by 


ADJUSTMENT    OF    THE    WEIGHTS.  41 

being  constantly  subjected  to  the  weight  of  the  beam  and 
pans,  and  that  they  may  suffer  no  sudden  injury,  from  undue 
violence  or  force  impressed  upon  any  part  of  the  balance. 
When,  therefore,  a  large  weight  of  any  kind  is  put  into,  or 
removed  from  the  pans,  it  should  never  be  done  without  pre- 
viously supporting  them  by  these  contrivances :  for  the 
weight,  if  dropped  in,  descends  with  a  force  highly  injurious 
to  the  supporting  edges;  or  if  a  large  weight  be  taken  out 
without  first  bringing  the  pans  to  rest,  it  cannot  be  done  with- 
out producing  a  similarly  bad  effect.  No  weight  heavier 
than  a  grain  should  be  introduced  without  this  precaution? 
which,  besides  being  requisite  for  the  reason  described,  is 
otherwise  advantageous. 

53.  When  a   weight  is  put   in  which  is  assumed  to  be 
nearly  equal  to  the  substance  to  be  weighed,  the  balance 
should  be  brought  to  a  horizontal  state  of  rest,  this  being 
usually  done  by  the  same  means  as  those  appointed  to  sup- 
port the  pans ;  it  should  then  be  liberated  gradually,  so  as 
to  leave  the  pans  wholly  supported  by  the  beam.  The  whole 
being  upon  its  true  centres  of  suspension,  it  will  be  observed 
whether  the  weight  is  sufficient  or  not,  and  the  rapidity  of 
ascent  or  descent  in  the  pan  containing  it,  will  enable   a 
judgment  to  be  formed  of  the  quantity  still  to  be  added  or 
removed  (43).     Bringing  the  balance  to  a  state  of  rest  as 
before,  such  quantity  should  be  added,  and  trial  again  made; 
and  it  is  better  to  repeat  this,  for  every  required  alteration  of 
weight,  however  small  it  may  be,  than  to  endeavour  to  ad- 
just the  weight,  whilst  the  whole  is  suspended  from  the  knife 
edges,  and  the  pans  are  swinging  in  the  air. 

54.  As  the  weight  approaches  to  equality  with  the  sub- 
stance to  be  weighed,  the  oscillations  become  slow,  and  the 
beam  ultimately  rests  in  a  line  more  or  less  inclined,  being 
the  same  with  that  above  and  below  which  the  oscillations 
are  made.     The  positions  of  this  line  may  be  judged  of, 
therefore,  whether  the  balance  be  at  rest  or  in  motion,  and 
is  a  material  indication  of  the  weight  to  be  added  or  taken 
away ;  a  person  who,  from  observation  of  the  oscillations  of 
a  balance  and  the  position  of  this  line,  is  able  to  take  ad- 
vantage of  the  indication  it  affords,  will  effect  the  required 

F 


42  SMALL    WEIGHTS ESTIMATION    OF    WEIGHTS. 

equilibrium  in  three  or  four  trials,  when  another  person,  un- 
observant of  these  points,  will  not  do  it  in  less  than  ten  or 
twelve.  The  small  weights  should  always  be  removed  by  a 
little  pair  of  pincers  (38),  for  when  the  fingers  are  used, 
there  is  frequent  risk  that  they  may  leave  something  ad- 
hering to  the  larger  weights  in  the  pan,  or  may  brush  out 
the  smaller.  The  weights  are  safer  too  in  pincers  than  in 
the  fingers. 

55.  It  sometimes  happens  that  the  balance  appears  to  vi- 
brate with  difficulty,  or  to  stick,  though  no  sufficient  cause 
can   be  discovered.     On  these  occasions   a  slight  tremor 
given  to  the  instrument,  by  tapping  on  the  case,  or  by  a  vi- 
bratory motion,  will  frequently  assist  the  balance,  and  con- 
fer sufficient  delicacy  to  allow  of  the  operation  being  com- 
pleted.    The  weight  should  always  be  estimated  when  the 
instrument  is  at  rest,  but  it  should  be  carefully  ascertained 
by  the  freedom  of  vibration,  that  this  rest  is  the  consequence 
of,  perfect  equilibrium,  and  not  due  to  the  want  of  delicacy 
in  the  instrument  or  to  accidental  obstruction. 

56.  When  the  balance  has  ultimately  been  brought  into  a 
state  of  equipoise,  the  weight  is  next  to  be  estimated.    The 
operator  generally  takes  an  account  of  the  additions  and 
subtractions  as   he    proceeds,   but   the   resulting  quantity 
should  be  confirmed  by  inspection.     Remove  the  weights, 
therefore,  from  the  balance,  and  if  there  be  many,  and  espe- 
cially small  ones,  this  is  best  done  by  slipping  them  all  out 
of  the  pan  together  into  a  small  basin,  or  upon  a  sheet  of 
paper,  and  then,  by  laying  them  out,  their  amount  may  be 
ascertained.     To  detect  any  error  that  may  have  arisen, 
either  in  calculation  or  otherwise,  make  up  the  quantity  in 
other  weights,  the  fewer  the  better,  introduce  these  into  the 
pan  in  place  of  the  former,  and  see  if  they  also  accurately 
counterbalance  the  substance  weighed  :  if  they  do,  the  ac- 
curacy of  the  weight  is  insured  ;  if  not,  the  cause  of  the  dis- 
crepancy must  be  sought  for,  discovered  and  corrected. 

57.  When  the  operation  of  weighing  has  to  be  repeated 
frequently,  as  happens  in  certain  parts  of  analytical  pro- 
cesses, it  economizes  time  to  have  the  smaller  weights  ar- 
ranged in  order  before  the  balance  ;  the  hundredths  together 


APPROPRIATION  OF  BALANCE  PANS.  43 

on  the  right  hand,  then  the  tenths,  then  the  grains  below  ten, 
and  ultimately  the  large  weights. 

58.  In  weighing  substances  that  are  hot,  great  attention 
should  be  paid  to  any  effect  produced  by  the  ascending  cur- 
rent of  air,  in  elevating  the  pan  containing  the  hot  material, 
and  thus  giving  erroneous  results  :  a  silver  capsule,  weighing 
600  grains  when  cold,  appeared  to  weigh  less  by  seven-tenths 
of  a  grain  when  heated  by  a  spirit  lamp,  and  again  placed  in 
the  scale.     If  it  had   previously  contained    ten   grains   of 
a  substance,  to  be  subjected  to  such  a  temperature,  a  loss  of 
about  0.7  of  a  grain  would   have  appeared  to  take  place, 
when  actually  none  might  have  occurred.     Besides  this  pro- 
bable fallacy,  the  introduction  of  a  hot  substance  or  vessel 
into  the  pan  is  liable  to  affect  the  arm  of  the  beam  above,  if 
delicately  constructed,  and  cause  derangement  for  the  time 
merely  by  its  expansion. 

59.  Although,  when  the  balance  is  in  perfect  order,  it  is 
indifferent  which  pan  receives  the  substance  and  which  the 
weights,  it  is  advantageous  always  to  use  the  same  pan  for 
the  same  purpose.     Attention  to  this  custom  is  a  correction 
to  a  certain  extent  for  inequality  in  the  length  of  the  arms; 
for  though  in  the  latter  case  a  difference  must  exist  between 
the  weight  and  its  counterpoise  to  produce  equilibrium,  yet 
this  difference  is  constant,  and  quantities  increased  or  di- 
minished   in  equal  proportions  will   equally  balance  each 
other,  so  long  as  the  contents  of  the  pans  are  not  changed. 
If  then  the  weights  are  always  put  into  one  pan,  the  quan- 
tities weighed  in  the  other  will  be  in  the  same  proportion  as 
the  weights,  though  not  exactly  equal  to  them  ;  and  the  pro- 
ducts of  an  analysis  estimated  thus  would  be  as  accurately 
known  as  if  the  balance  had  been  perfect.     But  if,  on  the 
contrary,  the  products  were  put  first  into  one  pan  and  then 
into  the  other,  they  would  sometimes  be  over-rated,   and 
sometimes  under-rated,  and  the  differences  would  very  soon, 
by  accumulation,    be  irreferable  either  to  the  weights  or 
each  other. 

60.  Attention  will  be  required  in  practising  this  rule  in 
cases  where  frequent  alterations  in  weight  are  taking  place. 
Suppose  carbonate  of  lime,  in  a  crucible,  had  been  weighed 


44  WEIGHING    OF    POWDERS ON    GLASS    OR    PAPER. 

in  the  substance  pan  by  weights  in  the  weight  pan  ;  if  it  were 
heated  violently  it  would  become  quick  lime,  and  lose  in 
weight,  but  this  loss  could  not  be  ascertained  correctly  by 
returning  the  crucible  and  lime  into  the  same  pan  it  was  in 
before,  and  then  adding  weights  to  make  up  the  deficiency, 
but  must  be  done  by  removing  weights  from  the  weight  pan  ; 
and  if  a  second  alteration  were  effected  in  the  weight,  as  by 
converting  the  lime  into  a  hydrate  or  sulphate,  that  must  also 
be  estimated  by  weights  added  to  the  weight  pan,  no  weights 
ever  being  mingled  in  the  same  pan  with  the  substance,  but 
every  change  in  the  weight  of  the  substance  being  estimated 
in  the  one  pan  by  a  corresponding  change  of  weight  in  the 
other. 

61.  When  weighing  powders,  or  moderately  divided  mat- 
ter, it  is  better  not  to  lay  them  at  once  on  the  pan,  but  upon 
some  interposed  substance.  For  this  purpose,  two  slips  or 
pieces  of  glass,  or  two  watch  glasses,  of  equal  weight,  should 
be  used,  one  in  the  weight  scale,  and  one  in  the  substance 
scale.  They  are  easily  preserved  clean,  and  possess  the  ad- 
vantage of  generally  resisting  chemical  action,  and  permitt- 
ing the  substance  to  be  washed  off  them  without  injury.  Or, 
in  place  of  two  pieces  of  glass,  one  piece,  or  a  little  Wedge- 
wood's  basin  counterpoised,  will  answer  the  purpose.  But 
two  pieces  of  paper  are  generally  more  convenient,  and  there 
are  few  substances  which  may  not  be  weighed  upon  them. 
Hot-pressed  wove  paper  is  the  best;  its  smooth  surface  pre- 
venting adhesion  even  of  the  finest  powders.  It  should  not 
be  torn,  but  cut,  for  the  fragmented  edge  would  retain  a 
portion  of  the  powder  when  passing  over  it ;  its  form  is  given 
and  its  adjustment  easily  made  by  a  pair  of  scissors.  Its 
flexibility  is  very  convenient  in  assisting  to  convey  powders 
into  a  flask,  or  other  narrow-mouthed  or  small  vessel.  All 
these  advantages  are  obtained  by  the  use  of  a  material, 
which  has,  in  addition,  those  of  being  very  cheap  and  clean, 
and  the  few  cases  in  which  it  is  objectionable,  as  where  the 
substance  to  be  weighed  is  moist  or  deliquescent,  are  easily 
distinguished,  and  its  insufficiency  may  then  be  supplied  by 
the  use  of  glass  or  metal. 


USE    OF    SPATULAS    IN    WEIGHING.  45 

62.  In  transferring  small  quantities  of  powder  from  place 
to  place,  as  for  example  into  and  out  of  the  balance,  and 
adjusting  them,  spatulas  are  very  useful ;  and  one  of  platinum, 
for  this  and  other  purposes,  is  requisite  in  every  laboratory. 
It  may  be  about  half  an  inch  wide,  at  least  three  inches  long, 
and  so  thick  as  to  resist  considerable  force  without  bending; 
otherwise  it  will  not  be  the  generally  serviceable  instrumentit 
oughtto  prove.     For  those  who  are  inclined  to  indulge  in  the 
luxuries  of  chemistry,  a  pocket  knife,  with  a  platinum  blade, 
is  a  very  excellent  tool,  answering  many  of  the  purposes  of  the 
spatula  above  described.     With  reference  to  the  removal  of 
powders,  ivory  and  bone  spatulas  answer  the  purpose  well ; 
but  in  case  of  the  absence  of  all  these,  their  place  at  the  balance 
may  be  supplied  by  aslip  of  the  same  hot-pressed  wove  writing- 
paper  before  mentioned,  cut  from  the  sheet  with  scissors.     In 
effecting  the  ultimate    adjustment    of  the    quantity,    the 
smallest  portions  may  be  taken  by  it  from  the  heap  in  the 
scale,  and  by  a  slight  lateral  shake,  the  smallest  quantity 
may  be  dropped  from  it  into  the  pan :  copper  and  platinum 
foil  do  not  make  good  temporary  spatulas,  unless  bent  down 
the  middle,  for  they  are  apt  to  give  way  between  the  fingers, 
and  by  their  elasticity  to  scatter  the  substance. 

63.  It  is  not  necessary  in  weighing  out  given  quantities  of 
powder,  100  grains  for  instance,  to  bring  the  balance  to  rest 
every  time  a  little  of  the  substance  is  added  or  removed,  in- 
asmuch as  by  a  short  pratice  both  may  be  done  without  com- 
municating any  other  impulse  to  the  instrument  than  that 
resulting  from  the  alteration  of  weight. 

64.  In  using  the  balance,  the  operation  very  often  consists 
merely  in  counterpoising,  no  estimate  of  the  quantity  being 
required,  but  simply  an  accurate  and  temporary  weight  cor- 
responding to  that  of  the  substance  or  vessel.     Platinum  cru- 
cibles, capsules,  glass  tubes,  &c.,  either  alone  or  with  their 
contents,  very  frequently  require  to  have  their  weights  thus 
compensated ;   for  counterpoises    should    be  considered  as 
weights,  and  go  into  the  weight  scale.     If  but  a  small  one 
be  required,  a  slip  of  tin  foil,  leaf  lead,  or  even  of  paper  or 
card,  will  answer  the  purpose  very  well,  the  piece  being 


46  COUNTERPOISING WEIGHTS     USEFUL. 

trimmed  down  by  scissors  till  it  balances  the  object  in  the 
other  pan.  If  a  larger  one  is  wanted,  a  piece  of  plumber's 
sheet  lead  is  convenient,  and  may  be  accurately  adjusted  by 
a  pocket  knife.  Besides  sheet  lead,  shot  of  different  sizes 
(39)  are  often  used  for  this  purpose,  being  poured  into  the 
weight  pan  until  there  is  nearly  sufficient  to  balance  the  con- 
tents of  the  opposite  scale,  and  the  final  adjustment  made 
by  a  piece  of  lead,  or  tin  foil,  or  paper.  When  shot  are  not 
at  hand,  the  counterpoise  may  be  nearly  made  up  by  large 
weights,  and  adjusted  as  before  by  metal  foil.  Where  the  whole 
consists  of  many  parts,  it  is  desirable  that  they  should  be  pre- 
served compactly  together,  lest  any  portion  be  dispersed,  and 
inaccuracy  introduced.  The  hollow  weights  (37)  are  for  this 
reason  very  useful  in  counterpoising; the  largest  weight  that 
is  not  too  heavy  should  be  taken,  and  the  requisite  addition 
placed  within  it.  If  such  a  convenience  be  not  present,  then 
perhaps  the  best  plan  is  to  put  a  piece  of  clean  smooth  paper 
(writing  paper  if  ready)  of  a  few  inches  square,  into  the  pan, 
in  the  first  place,  and  add  weights  to  complete  the  counter- 
poise ;  the  ultimate  adjustment  can  be  made  as  before,  or 
even  upon  the  edge  of  the  piece  of  paper ;  when  that  is  done, 
enclose  the  loose  portions  of  the  counterpoise  in  the  piece  of 
paper,  wrapping  all  up  safely  together,  again  see  that  it  is 
accurate,  and  then  set  it  aside  in  the  drawer  of  the  balance, 
or  in  the  place  appointed  for  such  things, until  it  is  required. 
In  consequence  of  the  change  in  weight  of  paper,  either  by 
desiccation  in  a  dry  place,  or  the  absorption  of  moisture  in 
a  damp  one,  a  counterpoise  so  wrapped  up  should  be  kept 
in  a  place  similar  in  dryness  to  that  from  whence  the  paper 
came,  and  the  chances  of  change  are  diminished  as  the 
time  is  less  during  which  it  is  necessary  to  be  preserved. 
When  the  mind  is  alive  to  this  source  of  error,  it  is  easily 
avoided,  by  keeping  paper  for  the  purpose  in  the  place  where 
counterpoises  are  kept,  or  by  drying  the  paper  and  keeping 
the  counterpoises  also  in  a  dry  state. 

65.  Sometimes  vessels  or  substances  are  to  be  weighed 
which  will  not  conveniently  rest  in  the  pans  without  a  little 
contrivance  :  tubes,  if  long,  now  and  then  interfere  with  the 
case  containing  the  balance,  and  flasks  are  liable  to  roll  over, 


SUSPENSION    FROM    THE    PANS.  47 

occasioning  the  loss  of  their  contents.  Tubes  of  moderate 
length,  such  for  instance  as  are  used  in  the  processes  of  or- 
ganic analysis,  can  often  in  these  cases  be  weighed  by  the  use 
of  a  small  loose  loop  or  ring  of  twine,  which,  being  slipped 
over  the  suspending  wires  of  the  balance  pan,  is  to  be  raised 
nearly  to  the  top,  and  then  by  passing  the  tube  through  it, 
the  upper  part  will  be  supported,  whilst  the  lower  end  rests 
in  the  pan,  the  whole  being  in  a  position  approaching  to  the 
vertical.  In  this  case  it  is  necessary  that  the  loop  and  tube 
be  arranged  so  that  the  latter  does  not  touch  the  beam,  or 
in  any  way  interfere  with  the  free  suspension  of  the  pan  sup- 
porting it. 

Such  a  loop  is  also  very  convenient  in  supporting  flasks 
in  the  balance,  for  being  allowed  to  descend  upon  the  sus- 
pending wires  of  the  pan,  it  prevents  the  neck  of  the  flask 
from  passing  between  them,  and  retains  it  in  a  position  suf- 
ficiently vertical  to  avoid  the  loss  of  any  of  its  contents. 

66.  Many  balances,  in  order  to  facilitate  their  various 
uses,  have  a  hook  at  the  bottom  of  each  pan:  to  this  a  thread 
or  wire  is  readily  attached,  and  being  terminated  beneath  in 
one  or  more  loops,  is  easily  made  to  sustain  a  tube  or  other 
article  to  be  weighed,  which  from  its  inconvenient  shape  will 
not  lie  safely  in  the  pan  itself. 

67.  When  it  is  required  to  weigh  liquids,  they  must  of 
course  be  retained  in  some  convenient  vessel,  the  weight  of 
the  vessel  being  either  known,  or  counterpoised,  in  the  first 
place,  or  ascertained  by  an  after  operation.     Glasses,  flasks, 
capsules,  and  small  tubes,  are  all  useful  in  turn  to  contain 
fluids.     The  glasses  and  capsules  will  stand  readily  in  the 
pan,  and  the  flask  may  be  supported  as  before  mentioned 
(65)  by  the  loop  of  twine,  or  by  being  placed  upon  a  small 
wooden  ring  about  two  inches  in  diameter,  and  an  inch  wide, 
covered  with   list,  which   serves  as  a  temporary  foot  (68). 
The   tubes  will    more    frequently   be   required    to  contain 
scarce  fluids,  or  perhaps  such  as  have  actually  been  formed 
in  them  during  an  experiment,  and  will  often  require  sup- 
porting.    It  is  for  this  and  for  many  purposes  of  adjustment 
at  the  balance,  convenient  to  have  two  rings  of  good  cork, 
about  three  quarters  of  an   inch   high,  kept  with  it,  fitting 


48      SUPPORTING  RINGS — ADJUSTMENT  OP  FLUIDS. 

loosely  into  each  other,  and  having  for  the  internal  diameter 
of  the  small,  half  an  inch;  and  for  the  external  diameter 
of  the  larger,  two  inches.  These  will  support  most  tubes  in 
a  more  or  less  inclined  position ;  and  in  any  case  where  they 
will  not  answer  the  purpose,  a  temporary  stand  is  easily 
made  out  of  a  cork,  by  piercing  a  hole  through  it  with  a  rat- 
tail  rasp,  of  the  proper  size  to  receive  the  tube. 

68.  The  listed  rings  referred  to  (67)  are  exceedingly  use- 
ful in  the  laboratory  for  the  support  of  retorts,  flasks,  globes, 
receivers,  and  all  vessels  of  a  circular  form.  They  are  easily 
made  out  of  a  slip  of  thin  pliant  wood,  or  a  piece  of  sheet 
copper,  the  rough  ring  being  covered  by  rolling  list  round  it. 
A  number  of  them  should  be  provided  for  laboratory  pur- 
poses, from  two  to  six  inches  in  diameter,  and  of  different 
heights.* 

69.  Where  a  certain  weight  of  fluid  is  wanted,  its  final 
adjustment  is  easily  effected  by  several  methods.     If  it   be 
water  or  alcohol,  or  a  substance  that  does  not  act  upon  paper, 
it  is  best  to  add  a  little  over  weight,  and  then  to  remove  the 
excess  by  bibulous  paper.     If  a  piece  of  filtering  paper  be 
folded  up  several  times  in  the  same  direction,  it  will  form  a 
loose  rod,  the  end  of  which  being  dipped  into  the  fluid,    ra- 
pidly imbibes  a  quantity  by  its  porosity  and  capillary  attrac- 
tion :  when  it  has  arisen  about  an  inch  in  the  paper,  which  it 
will  do  instantly,  if  the  moist  piece  be  pulled  off  and  the 
fresh  end  again  immersed,  a  second  portion  will  be  taken. 
Upon  pulling  off  the  moist  end,  especially  if  done  by  a  hard 
pinch  extending  slightly  over  the  dry  part  above,  a  ragged 
extremity  is  left,  which  by  a  little  management  in  dipping 
the  paper  into  the  fluid  obliquely,  may  have  a  pointed  form 
given  to  it.     This  may  be  used  in  removing  either  large  or 
small  quantities,  and  is  very  convenient  for  the  final  adjust- 


*  The  best  form  of  an  aperture  for  the  support  of  globular  vessels  is  the 
triangular,  which  always  with  certainty  touches  them  at  three  points ;  whereas 
a  ring  often  gives  support  but  to  two  points.  By  cutting  off  the  angles, 
which  extend  unnecessarily  far,  a  hexagonal  figure  of  three  longer  and  three 
shorter  sides  is  produced,  in  which  vessels  stand  securely,  and  in  any  desi- 
rable position.  When  such  a  form  of  aperture  is  used  for  lamp-stands,  it  does 
not  like  the  ring  throw  off  the  flame  or  heated  air,  but  permits  its  continuous  con- 
tact with  the  sides  of  the  vessel.  ED. 


ADJUSTMENT  OF  FLUIDS BY  ROD BY  TUBE.       4& 

ment  of  the  weight:  by  allowing  only  a  few  of  the  filaments 
which  remain  to  enter  the  fluid,  the  latter  passes  up  slowly, 
and  its  quantity  may  be  judged  off  by  the  gradual  progress 
of  the  moisture  above  ;  so  that  with  very  little  trial  the  pre- 
cise quantity  required  may  be  removed.  Such  at  least  is  the  * 
case  with  water  and  most  aqueous  solutions.  With  alcohol, 
fixed  and  volatile  oils,  it  is  not  so,  because  the  imbibed  part 
does  not  separate  with  particular  facility  from  the  dry  por- 
tion, or  leave  the  useful  filamentous  edge  spoken  of.  The 
final  adjustment  is  here,  however,  easily  made  by  a  slip  of 
paper  folded  once  or  twice,  or  by  other  means  to  be  de- 
scribed. 

70.  There  is  no  difficulty  in  the  rough  adjustment  of  any 
fluid ;    for   even  when  corrosive,  the  larger  portions   may 
be  removed  by  dipping  into  it  a  small  capsule  or  spatula  : 
in  these  cases  the  final  adjustment  may  be  completed  by  tak- 
ing up  the  small  remaining  excess  by  means  of  a  glass  rod. 
Upon  dipping  a  rod  into  a  fluid  and  withdrawing  it  rapidly, 
as  much  as  would  be  contained  in  three  or  four  drops,  may 
be  readily  and   neatly   removed ;    the   rod  being  cleaned, 
more  may  be  taken  away  by  the  same  process  :  as  the  quan- 
tity removed  is  proportionate  in  some  measure  to  the  mois- 
tened surface  of  the  rod,  it  is  evident  that  by  using  one  which 
is  conical  at  the  end,  the  smallest  desired  quantity  may  be 
taken  up  at  once,  and  the  adjustment  accurately  effected.* 

71.  One  other  mode  of  adjustment  it  may  he  well  to  men- 
tion, leaving  the  many  varieties  which  may  be  conveniently 
devised,  as  occasion  may  offer,  for  spontaneous  suggestion. 
It  is'sornetimes  necessary  to  weigh  out  a  certain  portion  of 
a  fluid,  which,  from  being  a  new  product  or  the  result  of  a 
peculiar  experiment,  and  smaH  in  quantity,  will  not  admit  of 
the  slightest  waste.     A  tube  about  the  eighth  or  tentli  of  an 
inch  in  diameter,  drawn  out  to  a  capillary  termination,  is 
then  very  convenient.     If  its  fine  extremity  be  immersed  in 
the  fluid,  which  we  will  consider  as  in  excess  in  the  balance, 
capillary  attraction  causes  a  portion  of  it  to  enter  the  tube; 

*  Dr  Hare  forms  a  very  convenient  instrument  by  attaching  to  the  larger 
end  of  the  tube  delineated  in  paragraph  71,  a  small  bottle  of  gum  elastic, 
by  means  of  which  he  can  at  pleasure  fill  or  empty  the  tube.  ED. 

G 


50 


WEIGHING    SUBSTANCES    WHICH   CHANGE    IN    AIR. 


if  enough  be  not  removed  by  inclining  the  tube,  more 
will  enter  in  consequence  of  the  diminished  perpendicu- 
lar height  of  that  within ;  if  too  much  be  removed  by 
the  second  insertion,  an  elevation  of  the  tube  into  a  po- 
sition more  perpendicular  will  cause  the  passage  of  a 
portion  from  it  into  the  vessel ;  and  in  this  way  more 
or  less  may  be  taken  away  and  accurate  adjustment 
obtained.  Should  the  fluid  be  tardy  in  its  motion  with- 
in, from  the  dryness  of  the  interior  or  the  smallness  of 
the  lower  aperture,  it  may  be  helped  while  passing 
in  or  out,  by  applying  the  mouth  of  the  operator  to  the 
upper  orifice  ;  but  this  should  be  avoided  generally,  lest 
any  portion  of  moisture  be  introduced.  When  it  is  neces- 
sary to  lay  the  tube  down,  it  may  be  placed  in  a  position 
nearly  horizontal  across  a  glass  or  ring  (68),  or  any  ready 
support,  the  lower  small  extremity  being  out  of  contact  with 
any  other  substance.  When  the  operation  is  finished,  the 
quantity  which  ultimately  remains  upon  the  tip  of  the  tube, 
the  only  part  that  has  at  any  time  been  immersed,  is  so  small 
as  to  be  no  object,  and  this  is  the  whole  of  the  waste  incurred. 
The  portion  remaining  within  the  capillary  tube  is  to  be 
restored  to  what  is  left  of  the  original  quantity. 

72.  Peculiar  management  is  required  in  estimating  the 
weight  of  certain  substances  which  rapidly  undergo  change, 
and  are  hence  liable  to  alterations  in  weight  during  the  time 
occupied  in  the  performance  of  the  operation.  Suppose,  for 
instance,  it  were  necessary  to  weigh  some  hydrate  of  chlo- 
rine obtained  by  compressing  the  moist  chrystals  produced 
at  temperatures  below  40°,  within  folds  of  cold  bibulous  pa- 
per; or  that  the  weight  of  hydrated  chloride  of  calcium  in 
crystals,  and  dried  in  the  same*  manner,  by  compression  were 
required ;  the  first  would  evaporate  in  the  air,  and  not  only 
injure  the  balance  and  neighbouring  bodies,  but  also  lose 
weight ;  and  the  latter,  by  deliquescing,  would  gain  weight ; 
both  with  such  rapidity  as  entirely  to  prevent  the  attainment 
of  accuracy.  These  effects  will  be  completely  avoided  by  trans- 
ferring them,  not  to  the  pan  of  the  balance,  but  to  a  por- 
tion of  water  of  known  weight,  and  ascertaining  the  increase 
of  weight  so  occasioned.  In  such  a  case,  therefore,  weigh 
or  counterpoise  a  portion  of  water  in  a  test  glass  or 


WEIGHING  INDETERMINATE  QUANTITIES.  51 

• 

basin,  and  then,  the  crystals  being  prepared  and  dried  by 
compression,  transfer  them  rapidly  to  the  Water,  and  ascer- 
tain their  quantity  by  the  increase  of  weight ;  then  proceed 
with  the  analysis  or  experiment,  using  the  solution  in  place 
of  the  crystals.  It  is  evident  that  an  expedient  of  this  kind 
has  its  limits,  consisting  in  the  nature  of  the  experiment  to 
be  made,  and  the  action  of  the  water  on  Jhe  substances  ;  but 
it  is  often  very  valuable,  and  now  and  then  removes  a  diffi- 
culty which  could  not  otherwise  be  surmounted.  The  choice 
of  the  substance  which  is  to  receive  the  changeable  body 
must  depend  upon  circumstances ;  and  sometimes  alcohol, 
sometimes  water,  and  sometimes  an  acid,  alkaline,  or  neutral 
solution  is  to  be  preferred. 

73.  It  may  here  be  observed,  that  as  in  many  experiments, 
one  quantity  is  equally  convenient  with  another,  so  that  it 
be  accurately  known,  we  have  the  advantage  in  such  cases 
of  avoiding  any  trouble  dependant  upon  adjusting  accurately 
the  quantity  of  matter,  and  obtain  the  same  end  by  adjusting 
the  weights,  the  matter  itself  being  left  undisturbed.  Thus  if 
it  were  wished  to  know  how  much  chloride  of  silver  would  be 
furnished  by  a  given  weight  of  crystalline  hydrated  chloride 
of  calcium,  76.43,  or  any  other  number  of  grains,  would  an- 
swer the  purpose  as  well  as  an  accurate  hundred,  and  the 
facility  of  immersing  the  body  in  water  as  above  described 
is  obtained.     The  particular  cases  where  an  opportunity  of 
this  kind,  dependant  upon  the  adjustment  of  the  substance 
or  the  weight  at  pleasure,  can  be  taken  advantage  of,  must 
depend  upon  the  judgment  of  the  experimenter. 

74.  Similarly  changeable  products,  the  weights  of  which 
are  required,  are   frequently  produced  in  vessels,  and  espe- 
cially in  tube  operations.     In  such  cases  the  method  will  be 
to  counterpoise  or  weigh  the  vessel  and  its  contents,  then  to 
remove  the  substance,  and,  cleaning  the  vessel,  to  ascertain 
the  loss  of  weight;  that  being  the  weight  of  the  substance. 
Wherever  such  a  course  is  necessary,  the  use  of  vessels  that 
may  be  cleaned  without  injury  or  change  is  evidently  need- 
ful :  hence  a  great  advantage  of  tubes  and  vessels  of  glass, 
or  platinum  crucibles  and  capsules. 

75.  Substances  which  fume,  and  which  may  in  conse- 


52  MODE  OF  WEIGHING  VOLATILE  FLUIDS. 

£ 

quence  cause  injury  to  the  balance,  should  be  weighed  in 
close  vessels.  Of  such  kind  are  some  of  the  acids,  ammonia, 
and  numerous  mixtures. 

76.  Small   capillary  tubes,  made  by  drawing  out  a  piece 
of  thin  quill  glass  tube  at  the  blow-pipe,  as  hereafter  to  be 
described  (Sect,  xx),  are  exceedingly  convenient  for  the  es- 
timation of  minute  quantities  of  valuable  liquid  products,  or 

moderately  but  not  excessively  volatile 
substances,  such  as  ether,  &c.  :  the  tube 
may  be  of  the  general  form  of  that  depicted  in  the  woodcut, 
and  of  the  same  size  or  larger,  as  may  be  convenient ;  hav- 
ing been  counterpoised,  it  is  to  be  charged  with  the  fluid  to 
be  weighed,  by  dipping  into  it  the  smaller  extremity,  and 
inclining  the  tube.  When  a  sufficient  quantity  has  entered  by 
capillary  attraction,  the  tube  is  to  be  withdrawn,  the  small 
portion  o.f  external  moistened  surface  wiped,  and  the  whole 
weighed,  care  being  taken  that  the  end  does  not  touch  any 
substance,  for  then  the  fluid  may  be  drawn  out.  In  this 
way  the  quantity  can  be  accurately  ascertained,  and  then, 
that  the  experiment  may  include  all  weighed,  it  will  be  found 
of  advantage  if  the  tube,  being  of  no  consequence  to  the  re- 
sult, may  be  thrown  with,  its  contents  into  the  solvent,  or 
added  directly  to  the  substance  upon  which  the  action  is  to 
take  place  :  the  tube  itself  being  broken  up  and  disregarded. 

77.  Sometimes  it  is  desirable  hermetically  to  close  one 
end  or  even  both  ends  of  the  tube  charged  as  above  ;  this  is 

easily  done  by  having  it  of  the  an- 
nexed form,  the  capillary  termin- 
ation being  rather  wider  than  the  part  a  little  above  it.  In 
this  case  when  the  tube  is  filled  as  far  as  is  desirable,  by 
inclining  or  inverting  it,  the  substance  in  the  narrow  part  will 
leave  the  extremity,  and  this  being  introduced  for  a  moment 
into  the  flame  of  a  spirit  lamp  will  be  effectually  sealed ; 
this  done,  the  fluid  is  to  a  great  degree  secured  and  ren- 
dered stationary  in  the  tube,  and,  if  required,  it  is  easy,  by 
approaching  the  other  end  to  a  spirit  lamp,  to  soften  the 
glass,  draw  it  out,  and  seal  it,  in  the  manner  to  be  shewn 
hereafter.  ?••*•• 


SPECIFIC   GRAVITY.  53 

79.  Where  in  place  of  any  particular  weight,  merely  an 
equal,  double,  or  triple  quantity  of  one  substance  is  wanted 
to  be  added  to 'another,  a  convenient  quantity  of  the  one 
most  worthy  of  consideration  may  be  put  into  one  pan,  and 
counterbalanced  once,  twice,  or  thrice,  by  the  other.  In 
mixing  dry  substances,  or  in  making  analyses  with  refer- 
ence to  the  kind  rather  than  the  weight  of  bodies  present, 
this  comparative  mode  of  estimation  is  frequently  useful. 

79.  In  most  processes  of  weighing,  the   buoyancy  of  the 
air  is  overlooked,  and  though,  in  consequence  of  the  very 
superior  density  of  solid  and  fluid  matter  generally,  as  com- 
pared to  the  atmosphere  around  us,  errors  thus  introduced 
are  usually  unimportant,  yet  the  chemist  should  be  aware  of 
its  influence,  and  alive  to  its  possible  interference.     From 
the  manner  in  which  gases  are  usually  weighed,  the  error 
does  not  then  exist,  but  it  is  sometimes  more  considerable 
than  would  be^expected  in  experiments  made  with  substan- 
ces, at  one  time  in  the  gaseous  state,  and  at  another  in  the 
liquid  or  solid  form.     The  production  of  water,  for  instance, 
from  the  combination  of  oxygen  and  hydrogen,  is  an  im- 
portant experiment,  and  has  been  often  repeated ;  the  weight 
of  the  water  should  accurately  correspond  with  the  weights 
of  the  gases  combined.     The  weights  of  the  gases  are  in  the 
usual  method  correctly  ascertained,  but  the  weight  of  the 
water  estimated  in  the  usual  way  is  diminished  by  the  buoy- 
ancy of  the  air,  which  in  this  case  amounting  to  about  -g-J^th 
part,  would  introduce  an  error  to  that  extent,  were  this  ef- 
fect not  to  be  taken  into  account. 

80.  The  determination  of  specific  gravity  is  of  constant 
occurrence  with  the  chemist,  and  though  it  resembles  the 
general  operation  of  weighing,  there  are  peculiarities  con- 
nected with  it  which  require  attention.     It  is  not  intended 
here  to  go  into  a  consideration  of  the  general  process,  but, 
leaving  that  to  be  obtained  from  elementary  works,  only  to 
notice  those  things  which  occasionally  give  rise  to  errors,  or 
are  necessary  to  correct  results.     If  the  substance  be  a  solid, 
the  well-known  process  $f  weighing  it  first  in  air  and  then  in 
water,  and  dividing  the  first  weight  by  the  loss  in  the  second, 
is  to  be  followed;  and  though  here  again  minute  errors  are 


54  SPECIFIC  GRAVITY; — SUSPENDING  LINE. 

introduced  in  consequence  of  the  buoyancy  of  the  air  fn  the 
first  weighing,  they  are  not  of  a  nature  to  require  attention 
in  this  place. 

81.  Balances  are  expressly  furnished  with  contrivances  to 
facilitate  the  immersion  of  the  body  in  water,  when  required, 
so  that  its  weight  may  be  ascertained  in  that  position.     The 
substance  which  passes  the  surface  of  the  water,  supporting 
the  immersed  body  and  connecting  it  with  the  scale  beam,  is 
generally  ahorse  hair,  and  for  common  purposes,  it  is  perhaps 
the  best.     When,  however,  a  hydrostatic  balance   is  not  at 
hand,  and  an  ordinary  balance  is  to  be  used  for  the  purpose, 
the  suspending  link  has  frequently  to  be  selected  from  several 
substitutes  which  present  themselves  in  the  laboratory.     It 
should  not  be  penetrable  or  alterable  by  the  water ;  it  should 
not  be  thick;  it  should  not  be  weak.     If  it  be  the  first,  as  a 
piece  of  thread  for  instance,  the  quantity  of  water  in  it  under- 
goes continual  variation  in  consequence  of  th£  difference  of 
immersion  as  the  balance  vibrates,  and  thus  a  change  of  weight 
is  occasioned  in  that  which  ought  to  be  constant.     If  it  be  the 
second,  as  a  piece  of  string,  it  introduces  errors  of  two  kinds, 
one  dependant  on  the  buoyant  power  of  the  water  over  the 
part  which  is  sometimes  immersed  and  sometimes  not,  and 
which  if  the  same  point  were  not  always  brought  to  the  sur- 
face of  the  water  would  act  upon  it,  as  it  would  upon  the  stem 
of  the  hydrometer  (103);  the  other  dependant  upon  the 
capillary  attraction  of  the  water,  which,  within  certain  limits, 
would  cause  a  larger  elevation  of  the  fluid  round  the  string 
when  thick,  than  if  it  were  small,  and  add   a  proportionate 
weight  to  it.     If  it  were  the  third,  it  would  present  an  ob- 
stacle to  the  correction  of  the  faults  last  mentioned,  inas- 
much as  it  would  not  admit  of  being  made  thin  for  want  of 
strength. 

82.  These  errors  become  serious  when  they  affect  a  small 
body,  a  gem  for  instance,  and  in  such  cases,  or  wherever  the 
weight  will  admit  of  its  application,  a  filament  of  unspun  silk 
is  probably  the  best  substance  that  can  be  used.     It  is  unaf- 
fected by  the  water;  has  scarcely  any  weight,  or  any  buoy- 
ancy given  to  it  by  immersion  in  the  fluid,  so  minute  is  its 
bulk ;  it  does  not  cause  any  sensible  elevation  of  fluid  round 


SPECIFIC  GRAVITY IMMERSION  IN  WATER.  55 

it  where  it  cuts  the  surface  of  the  liquid,  and  retains  no  air- 
bubbles.  It  has  but  little  strength  in  consequence  of  exces- 
sive tenuity,  and  therefore  must  not  be  pulled  hastily  or  sub- 
jected to  sudden  snatches. 

83.  When  a  silk  fibre  will  not  answer  the  purpose,  or  can- 
not be  obtained,  a  fine  wire  will  very  conveniently  supply  its 
place  ;  and  it  is  only  in  cases  of  necessity  that  recourse  should 
be  had  to  thread,  fine  twine,  or  any  substance  made  up  of 
numerous  fibres.     But  if  some  of  the  latter  must  answer  the 
purpose,  then  silk  thread  is  better  than  any  other,  because  of 
its  strength ;  and  what  is  called  thrown  silk,  which  consists  of 
a  few  fibres  only,  twisted  together,  is,  when  strong  enough, 
almost  unobjectionable.     In  all  these  cases  of  substitution, 
take  that  substance  which,  being  of  sufficient  strength,  is  the 
thinnest  and  most  compact,  and  in  all  cases  it  is  desirable  that 
the  mass  of  which  the  specific  gravity  is  to  be  taken  should  be 
as  large  as  the  line  will  safely  support;  for  if  a  coarse  sus- 
pending thread  be  used  in  taking  that  of  asmall  fragment,  the 
errors  relating  to  the  thread,  which  are  several  in  number, 
affect  the  result  much  more  importantly  than  if  the  operation 
had  been  performed  upon  a  large  piece. 

84.  There  are  several  points  relative  to  the  immersion  of 
the  body  in  the  water,  which  require  attention.     The  water 
must  be  distilled  for  delicate  experiments;  but  on  ordinary 
occasions,  when  that  cannot  be  obtained,  the  lightest  rain- 
water may  be  substituted,  or  in  common  cases  even  well  or 
spring  water  of  ascertained  purity.     Several  wells  are  known, 
amongst  which  are  the  deep  ones  of  London,  which  supply 
water  as  pure  or  purer  than  town  rain-water.     The  temper- 
ature of  the  water  and  the  substance  to  be  examined  should 
be  the  same?  or  otherwise  currents  will  be  produced,  which 
to  a  slight  degree  affect  the  results:  indeed,  all  delicate  ex- 
periments must  be  made  at  one  particular  temperature,  and 
60°  Fahrenheit  is  very  convenient  for  the  purpose.     A  con- 
siderable difference  of  temperature  at  different  times  pre- 
vents the  results  from  being  comparable  with  each  other. 

85.  The  body,  as  well  as  the  various  contrivances  for  its 
suspension,  constructed  by  the  instrument  makers,  such  as 
pincers,  forceps,  &c-  must  of  course  be  fully  immersed  in  the 


56  OSCILLATION  OF  THE  BALANCE. 

" 

water.  It  should  have  at  least  half  an  inch  of  the  fluid  around 
it  in  every  direction,  that  perfect  freedom  of  motion  in  the 
balance  may  be  obtained.  All  bubbles  of  air  adhering  to 
it  should  be  removed  by  a  hair  pencil.  Water  taken  from 
the  bottom  of  any  deep  portion  which  has  been  exposed  to 
contact  with  the  air  for  a  length  of  time,  will  frequently 
evolve  bubbles,  eitherspontaneously  or  upon  the  immersion  of 
a  rough  substance,  in  consequence  of  its  relief  from  the  pre- 
viously superincumbent  pressure.  Spring-water  drawn  from 
the  bottom  of  a  well  will  illustrate  this  effect,  which  is  very 
inconvenient  when  it  happens  with  such  water  as  is  used  for 
taking  specific  gravities  from  the  succession  of  bubbles  pro- 
duced. Exposure  to  the  air  for  an  hour  or  two,  or  pouring  it 
to  and  fro  in  a  broken  stream  several  times  in  the  air,  is  a 
remedy  for  the  evil. 

86.  The  oscillations  of  the  balance,  though  much  slower 
than  those  which  occur  when  the  body  is  weighed  in  air, 
should  be  quite  free.     Supposing  the  balance  to  be  in  good 
order,  and  the  body  suspended  with  perfect  liberty  in  the 
water,  neither  touching  any  part  of  the  vessel  nor  approach- 
ing the  surface,  still  serious  obstructions  may  exist,  espe- 
cially when  the  substance  is  small,  the  balance  delicate  and 
the  suspending  link  thick.     Suppose  a  horse  hair  to  be  used 
for  suspension,  which  from  the  manner  in  which  it  is  wetted 
by  the  water,  causes  a  small  depression  on  the  surface  of 
the  fluid  around  it  as  it  descends,  and  a  little  elevation  as  it 
ascends.     Such  is  a  very  common. eflfect,  and   is  produced 
not  only  on  the  first  immersion  and  emersion  of  the  hair,  but 
is  repeated  at  every  ascent  and  descent,  within  certain  limits'. 

It  is  evident  that  this  will  very  seriously  retard  the  oscil- 
lations of  a  delicate  balance,  and  prevent  its  motion  either 
one  way  or  the  other  by  a  force  equal  to  the  weight  of  the 
little  elevation  of  water.  This  may  be  partly  corrected  by 
tapping  the  vessel  containing  the  water,  or  the  case  of  the 
balance,  so  as  to  occasion  a  slight  tremor.  Whenever  it 
happens,  the  equilibrium  should  not  be  considered  as  obtain- 
ed; unless  the  water  have  a  plain  surface  at  the  part  where 
it  surrounds  the  hair. 

87.  The  substance  used  as  a  support  always  becomes 


OSCILLATION  OF  THE  BALANCE SUSPENDING  LINE.  57 

wetted  by  immersion  in  the  water;  and  in  consequence  of  the 
extent  of  oscillation,  a  portion  of  the  wetted  part  is  constant- 
ly oat  of  the  water  when  the  balance  is  poised.  This  affects 
the  result  in  two  ways:  first  by  the  quantity  of  water  which 
adheres  to  it,  and  which  varies  in  proportion  as  it  has  been 
immersed  to  a  greater  or  smaller  depth,  or  as  it  is  imper- 
vious to  water  like  a  hair,  or  more  or  less  porous  like  thread ; 
secondly,  by  the  little  elevation  of  water  which  then  exists 
round  the  line  by  capillary  attraction,  and  which  is  the  same 
whether  more  or  less  of  the  part  above  has  been  wetted. 
The  weight  of  the  water  thus  raised  above  the  surface  is 
counterbalanced  by  an  equal  weight  in  the  opposite  pan; 
thus  an  error  to  that  extent  is  introduced,  which,  though  ge- 
nerally small,  may,  from  ignorance,  inattention,  or  the  minute 
size  of  the  piece  operated  with,  at  times  become  important. 

88.  Although  the  suspending  line  may  have  been  very  ac- 
curately compensated  in  the  air,  before  the  body  to  be  im~ 
mersed  in  water  was  attached  to  it,  yet  when  partly  immers- 
ed during  the  progress  of  the  experiment,  the  counterpoise 
is  no  longer  its  equivalent,  the  part  immersed  being  buoyed 
up  by  a  force  equal  to  the  weight  of  the  water  which  it  dis- 
places; and  this,  with  a  large  horse-hair,  or  a  still  coarser 
line  of  suspension,  would  be  important.  It  may  be  estimat- 
ed, as  well  also  as  the  effect  of  the  little  elevation  of  water 
before  spoken  of,  after  the  weighing  has  been  finished,  by 
removing  the  body,  again  immersing  the  hair  to  the  same 
depth  as  before,  allowing  it  to  be  wetted  to  the  same  degree, 
and  seeing  how  much  it  differs  from  its  weight  when  freely 
suspended  in  a  dry  state  in  the  air.  Balances  which  are 
fitted  up  with  apparatus  for  hydrostatical  experiments  have 
counterpoises  for  the  suspending  parts,  both  when  in  and  out 
of  the  water;  which  might  be  made  perfectly  accurate  were 
the  surface  of  the  water  always  brought  to  the  same  place  up- 
on the  suspending  line. 

All  these  errors  are  lessened  by  diminution  in  the  size  of 
the  suspension  line;  and  when  that  is  a  silk  filament,  they 
almost  disappear.  Hence  the  great  use  of  this  substance  in 
delicate  experiments,  as  those  made  with  small  gems,  minute 
globules  of  metal,  or  other  rare  substances. 
H 


58 


SPECIFIC  GRAVITY. 


89.  When  the  substance  of  which  the  specific  gravity  is  to 
be  taken  is  soluble  in  water,  some  other  fluid  of  known  spe- 
cific gravity  must  be  used,  which  does  not  dissolve  it.    There 
are  very  few  cases  which  may  not  be  met  by  alcohol,  oil  of 
turpentine,  or  olive  oil. 

90.  Not  unusually,  the  body  to  be  examined  is  porous  like 
coke,  or  divided,  as  in  sand  or  powders,  into  numerous  parts. 
In  these  cases,  a  beautiful  instrument  in  principle  has  been 
devised  by  M.  Say*,  in  which  soluble  as  well  as  insoluble 
substances  may  be  tried,  provided  they  do  not  give  off  vapour ; 
and  the  only  precautions  necessary  are  to  prevent  the  exist- 
ence of  cavities  unconnected  with  the   air,  and  to  destroy 
such  minute  cellular  structures  as,  like  that  of  charcoal, 
have  the  power  of  absorbing  gases  or  vapours.     It  is  proper, 
therefore,  to  reduce  the  substance  to  solid  fragments,  by 
breaking  it  down  coarsely,  or  pulverizing  it  more  or  less  in  a 
mortar. 

91.  Mr  Leslie,  who  at  a  much  later  period  thought  he  had 
invented  the  instrument,  published  an  account  from  which 
the  following  description  is  taken.  It  consists  of  a  glass  tube, 
a  e,  about  three  feet  long,  and  open  at  both  ends.     The  wide 

part,  a  6,  is  about  4- 10th  of  an  inch  in  diame- 
ter ;  the  part  be,  2-10ths.  The  two  parts 
communicate  at  b  by  an  extremely  fine  slit, 
which  suffers  air  to  pass,  but  retains  sand  or 
powder.  The  mouth  at  a  is  ground  smooth, 
and  can  be  shut  so  as  to  be  air-tight,  by  a  small 
glass  plate,/.  The  substance  whose  specific 
gravity  we  wish  to  find  (suppose  it  to  be 
sand)  is  put  into  the  wide  part  of  the  tube, 
a  6,  which  may  either  be  filled  to  the  top  or 
not.  The  tube  being  then  held  in  a  vertical 
position,  has  the  narrow  part  immersed  in  mercury,  contain- 
ed in  an  open  vessel  a;  till  the  metal  rises  within  to  the  gorge 
6.  The  lid  is  then  fitted  on  air-tight,  at  a.  In  this  state  it 
is  evident  there  is  no  air  in  the  tube,  except  that  mixed  with 


*  Annals  de  Chimie,  xxiii. ,  p.  1 ;  or  Nicholson's  Quart.  Journ.,  vol.  i.,p.  325, 


SAY'S  INSTRUMENT  FOR  POWDERS,  ETC.  59 

the  sand  in  the  cavity  a  6.  Suppose  the  barometer  at  the 
time  to  stand  at  30  inches,  and  that  the  tube  is  lifted  perpen- 
dicularly till  the  mercury  stands  in  the  inside  of  b  e,  at  a  point 
c,  15  inches  (or  one  half  30)  above  its  surface  in  the  open 
vessel,  it  is  evident  then  that  the  air  in  the  inside  of  the  tube 
is  subjected  to  a  pressure  of  exactly  half  an  atmosphere,  and 
of  course  it  dilates,  and  fills  precisely  twice  the  space  it  ori- 
ginally occupied.  It  follows,  too,  that  since  the  air  is  dilat- 
ed to  twice  its  bulk,  the  cavity  a  b  contains  just  half  of  what  it 
did  at  first;  and  the  cavity  b  c,  now  containing  the  other  half, 
the  quantity  of  air  in  each  of  these  parts  of  the  tube  is  equal : 
in  other  words,  the  quantity  of  air  in  &  c  is  exactly  equal  to 
what  is  mixed  with  the  sand  in  a  6,  and  occupies  precisely 
the  same  space  which  the  whole  occupied  before  its  dilation. 
Let  us  now  suppose  the  sand  to  be  taken  out,  and  the  same 
experiment  repeated — but  with  this  difference,  that  the  cavi- 
ty a  b  is  filled  with  air  only.  It  is  obvious  that  the  quantity 
being  greater,  it  will,  when  dilated  to  double.the  bulk  under 
a  pressure  of  15  inches,  occupy  a  larger  space,  and  the  mer- 
cury will  rise,  let  us  suppose,  only  to  d.  But  the  attenuated 
air  in  the  narrow  tube  always  occupies  exactly  the  space 
which  the  whole  occupied  at  ordinary  atmospheric  pressure; 
and  thisspace,  therefore, is  in  the  one  case  b  c,  and  in  the  other 
b  d.  Hence  it  follows,  that  the  cavity  c  d,  which  is  the  dif- 
ference between  these,  is  equal  to  the  bulk  of  the  solid  mat- 
ter  in  the  sand.  Now,  by  marking  the  number  of  grains  of 
water  held  by  the  narrow  tube  b  e  on  a  graduated  scale  at- 
tached to  it,  we  can  find  at  once  what  is  the  weight  of  a 
quantity  of  water  equal  in  bulk  to  the  solid  matter  in  the 
sand,  and  by  comparing  this  with  the  weight  of  the  sand,  we 
have  its  true  specific  gravity. 

When  this  apparatus  is  not  at  hand,  and  the  substance  is 
in  small  pieces,  it  must  be  supported  in  the  usual  way  by  a 
cup,  which  is  of  course  to  be  counterpoised  first  in  air  and 
then  in  water,  exactly  as  was  described  with  the  line  or  re- 
taining forceps  before  mentioned. 

92.  The  specific  gravity  of  fluids  is  ascertained  by  weigh- 
ing equal  bulks  of  them  at  the  balance,  or  by  the  immersion 
of  hydrometers  or  bulbs — bodies  which,  by  their  floating  or 


60  SPECIFIC  GRAVITY  OF  FLUIDS. 

sinking,  indicate  the  comparative  weights  of  the  substances 
into  which  they  are  introduced.  Bottles  are  usually  provid- 
ed by  the  instrument  maker  as  measures  of  the  bulk  of  fluid 
to  be  weighed ;  these  are  arranged  to,  hold  a  given  quantity 
of  distilled  water  expressible  by  weight,  in  round  numbers, 
as  1000,  800,  500,  280  grains,  &c.,  and  are  closed  by  a 
ground  stopper.  The  ultimate  adjustment  is  effected  by  re- 
moving portions  from  the  lower  surface  of  the  stopper,  so 
that  when  the  bottle  is  filled  with  water,  and  the  stopper 
put  into  its  place,  the  quantity  which  remains  in,  and  entire- 
ly fills  the  bottle,  is  of  the  bulk  required.  The  stoppers,  in- 
stead of  being  solid,  are  sometimes  made  of  a  piece  of  thick 
thermometer  tube  of  fine  bore,  the  intention  being  to  afford 
a  free  passage  for  the  excess  of  fluid  when  the  stopper  is 
forced  into  its  place.  This  answers  the  purpose  very  well 
with  water  and  less  volatile  fluids,  though  it  is  not  necessary; 
but  with  very  volatile  fluids,  as  alcohol,  ether,  &c.,  it  occa- 
sions an  evil.  It  does  not  merely  afford  a  small  surface  for 
evaporation,  but,  in  consequence  of  the  impossibility  of  grind- 
ing a  stopper  so  accurately  that  when  in  its  place  it  shall 
not  let  a  little  of  these  limpid  fluids  pass,  actually  accele- 
rates the  evaporation;  for  the  ether,  for  instance,  passing  by 
capillary  attraction  between  the  stopper  and  the  bottle,  eva- 
porates round  the  edge,  whilst  the  air  enters  in  a  constant 
succession  of  bubbles  by  the  centre  passage,  and  thus  a  rapid 
diminution  in  the  bulk  of  the  fluid  takes  place ;  whereas  if 
the  bottle  had  been  closed  by  a  solid  stopper,  although  the 
minute  ring  of  fluid  round  the  top  would  evaporate,  no  more 
would  be  able  to  rise,  because  air  could  not  enter  to  sup- 
ply its  place,  and  the  bulk  would  be  comparatively  un- 
changed. 

93.  Specific  gravity  bottles  are  constructed  of  various 
sizes,  and  are  each  accompanied  by  a  weight,  which  coun- 
terpoises the  bottle  full  of  distilled  water,  the  quantity  of 
water  required  for  the  purpose  having  been  ascertained  and 
marked  upon  it.  All  that  is  required  in  estimating  the  spe- 
cific gravity  of  any  other  fluid  is,  to  fill  the  bottle  with  it,  to 
ascertain  its  weight  by  observing  how  much  heavier  or 
lighter  it  is  than  the  weight  furnished  with  the  instrument, 


SPECIFIC   GRAVITY  BOTTLES.  61 

and  adding  and  subtracting  accordingly;  the  result,  divided 
by  the  weight  of  water,  will  be  the  specific  gravity.  It  is 
necessary,  in  these  experiments,  that  the  temperature  be  ob- 
served, or  rather,  indeed,  when  convenient,  that  they  be 
made  at  the  same  temperature,  or  it  will  not  be  possible  to 
compare  them  unless  previously  corrected  by  calculation, 
which  would  in  many  cases  be  difficult.  For  the  same  rea- 
son it  is  requisite  that  the  bottle  should  not  be  handled  by 
uncovered  hands,  lest  heat  be  communicated  to  it,  and  its 
bulk  and  the  volume  of  the  fluid  within  be  affected:  but  up- 
on introducing  the  stopper,  the  overflow  of  liquid  should  be 
wiped  off  with  a  clean  cloth,  which  may  be  used  at  the  same 
time  to  prevent  contact  with  the  hands;  and  in  transferring 
it  to  the  balance,  the  fingers  should  be  defended  in  a  similar 
way :  or  if  this  be  difficult,  from  any  particular  circumstance, 
they  must  not  on  any  occasion  touch  more  than  the  thick 
rim  of  glass  round  the  stopper. 

94.  It  is  further  necessary  that  the  bottle  contain  nothing 
but  the  particular  substance  to  be  weighed.     To  insure  this 
point,  it  is  requisite  that  it  be  washed   out  after  every  ex- 
periment, the  last  two  or  three  rinsings  being  made  with  dis- 
tilled water;  if  it  be  then  dried,  nothing  more  remains  to  be 
done,  upon  the  performance  of  a  new  experiment,  than  to 
put  in  the  liquid  and  to  weigh.     But  as  it  is  inconvenient 
and  unnecessary  at  all  times  to  dry  the  bottle,  as  when  the 
specific  gravity  of  several  solutions  are  to  be  taken   in   suc- 
cession, it  may,  on  such  occasions  be  left  moist  within ;  and 
then,  at  the  next  experiment,  if  the  substance  to  be  operated 
with  is  abundant,  and  one  that  mixes  with  water,  as  a  mine- 
ral water,  alcohol,  or  an  aqueous  solution,  all  that  is  neces- 
sary is,  that  the  bottle  should  be  rinsed  with  it  two  or  three 
times  before  it  be  filled  for  weighing.     If  it  be  a  substance 
that  is  scarce,  or  oily,  or  that  will  not  mix  with  water,  the 
bottle  must  be  washed  and  dried. 

95.  Instruments  procured  from  the  maker  should  be  verified 
by  the  purchaser  before  they  are  used.     For  this  purpose  the 
bottle  and  stopper  should   be  well  cleaned  and  dried,  and, 
being  brought  to  the  temperature  of  62°  Fahrenheit,  should 
be  counterpoised.     The  bottle  must  next  be  carefully  filled 


62       VERIFICATION  OF  BOTTLES — SPECIFIC  GRAVITY  BULBS. 

with  pure  water  at  62°,  and  the  increase  of  weight  ascer- 
tained; this  is  the  weight  of  the  water,  and  should  corres- 
pond with  that  marked  on  the  weight  or  the  stopper  :  finally, 
the  counterpoise  and '  water,  weighed  together,  should  ex- 
actly balance  the  weight  sent  with  the  bottle.  If  the  maker 
graduates  the  bottles  at  any  other  temperature  than  62°,  it 
is  useless  to  expect  an  exact  accordance  with  estimates  made 
at  62°,  but  he  should  always  do  it  at  a  known  and  constant 
temperature,  with  which  the  purchaser  should  be  acquaint- 
ed; and  that  of  62°  Fahrenheit  is  for  several  reasons  better 
than  any  other.* 

96.  The  directions  given  for  the  verification  of  a  bottle, 
made  purposely  for  the  estimation  of  specific  gravities  of  li- 
quids, will  easily  enable  a  person  to  supply  its  want.  He  has 
but  to  select  a  small  well-stoppered  phial  of  convenient  capa- 
city, to  clean,  dry,  and  weigh  it,  and  then  to  ascertain,  as  be- 
fore, howmuch  water  it  will  hold;  the  weight  of  this  water  will 
be  a  divisor,  and  the  weight  of  any  other  fluid  filling  it,  a  di- 
vidend; the  quotient  will  be  the  specific  gravity  of  the  latter 
fluid. 

97.    Small   bulbs    blown  out   of   glass 
JJ~~]  tube,  or  even  small  thermometer  bulbs, 

like  those  figured  in  the  margin,  are  often 
useful  in  estimating  the  specific  gravity 
of  rare  fluid  products.     The   little   bulb 
represented  in  the  tube,  is  easily  made, 
as     is     hereafter    to    be    shown     (1198); 
and  having  been  counterpoised  and  fur- 
f      ^  nished  with  a  temporary  handle,  by  coiling 
\^__^/  a  piece  of  platinum  wire  round  it,  may  be 
warmed  by  a  spirit  lamp,  and  then  dipped 
into  the  fluid  in  the  tube;  as  it  cools,  a  portion  will  enter; 
upon  removing,  rewarming,  and  re-immersing  it,  a  second 

*  The  British  chemists  formerly  adopted,  in  common  with  all  the  world,  the 
temperature  of  60°  Fahr.  as  the  standard  temperature  of  distilled  water,  when 
used  to  ascertain  specific  gravity.  By  a  recent  act  of  Parliament,  62°  Fahr.  is 
made  the  standard  temperature  by  which  are  regulated  the  English  liquid  mea- 
sures. ED. 


Jt 


BULBS  FILLED- FLUIDS   HEATED  IN  TUBES.  63 

portion  may  be  introduced  by  the  same  mode  of  proceeding; 
a  small  bubble  of  air  will  ultimately  remain  within,  but  this 
may  be  expelled  by  warming  the  fluid  in  the  tube  with 
the  bulb  immersed  in  the  state  in  which  it  is  represented 
in  the  engraving;  the  liquid  will  expand  by  the  heat,  and 
force  out  a  part  of  the  air ;  then  by  immersing  the  bottom 
of  the  tube  in  water  to  lower  the  temperature  as  contraction 
takes  place,  the  fluid  will  enter  the  bulb.  A  second  or 
third  performance  of  the  heating  and  cooling  process  will  ef- 
fectually fill  the  vessel  with  liquid. 

98.  The  filling  of  bulbs  in  this  manner  is  very  often  re- 
quired in  certain  trains  of  research,  and  amongst  others  in 
organic  analysis.  Hence  it  is  necessary  to  point  out  one  or 
two  circumstances  requiring  attention  in  the  operation. 
When  the  bulb  is  about  four-fifths  full,  and  the  attempt  is 
made  to  fill  it  by  applying  heat  whilst  it  is  immersed  in  the 
liquid,  it  will  perhaps  be  found  that  the  bubble  of  air  expands 
and  contracts  as  its  temperature  changes,  but  does  not  go 
out  of  the  vessel;  the  fluid  which  enters  remaining,  by  capil- 
lary attraction,  in  the  narrow  part  of  the  top,  and  consequently 
passing  out  again  upon  the  re-elevation  of  tempera- 
ture. But  in  such  a  case  it  is  necessary,  before  the 
heat  is  applied,  to  make  this  portion  of  the  fluid  and 
the  air  change  places,  which  is  easily  done:  for  this 
purpose  the  tube,  with  its  contents,  should  be  held 
by  the  upper  part,  and  suffered  to  hang  as  it  were 
below  the  hand;  a  swing  of  a  foot  or  two  in  extent  should 
then  be  given  to  it,  so  as  to  produce  centrifugal  force;  all 
the  fluid  will  descend  except  that  which  is  contained  in  the 
narrowest  part  of  the  neck,  and  the  air  will  take  its  place; 
the  tube  and  bulb  should  then  be  heated  to  expel  more  air, 
and  fresh  fluid  suffered  to  enter,  which  is  to  be  treated  in 
the  same  way  if  required.  If  any  thing  renders  it  inexpedi- 
ent to  subject  the  whole  tube  to  this  motion,  the  bulb  can 
be  withdrawn,  and  being  held  by  the  wire  or  in  the  hand, 
can  then  be  shaken  in  the  same  way  and  with  the  same 
effect. 

99.  In  the  next  place  the  fluid  may  be  volatile,  and  sub- 
ject to  waste  by  repeated  elevations  of  temperature  in  an 


64  BULBS  EMPTIED. 

open  tube;  but  in  such  circumstances  it  is  easy  to  close  the 
tube  effectually  by  the  fore  finger  of  the  left  hand,  whilst 
the  thumb  and  second  finger  are  occupied  in  holding  it  (919): 
the  heating  and  cooling  are  then  to  be  performed  without 
allowing  the  end  to  be  unclosed,  and  no  waste  is  occasioned. 

100.  This  point  of   manipulation   will    require   a    little 
practice  to  allow  of  all  the  advantage  being  derived  from  it 
which  it  is  capable  of  affording  in  other  operations;  but 
when  required,  a  volatile  fluid,  ether  for  example,  may  be 
heated  until  its  vapour  has  a  force  of  two  or  even  three  at- 
mospheres, if  the  tube  be  strong  enough,  and  be  retained 
there  for  a  quarter  of  an  hour,  or  more,  without  any  loss. 
The  portion  of  common  air  in  the  tube  is  to  be  allowed  to 
escape  or  not,  according  to  circumstances  (919),  and  may 
be   made  use  of  at  times,  as  will  be  found  by  practice,  to 
prevent  the  accession  of  heat  to  the  fingers. 

101.  Returning  to  the  fluid  with  which  the  bulb  has  been 
filled: — upon  removing  the  latter  when  cold,  allow  its  exte- 
rior to  drain  as  much  as  possible;  the  wire  must  then  be 
taken  off,  the  surface  wiped,  and  the  bulb  put  upon  a  cork 
stand  (67),  and   weighed.     As  the  vessel  will  then  be  re- 
quired full  of  water,  it  must  be  emptied  of  the  fluid.     Re- 
place the  wire  handle,  invert  the  bulb,  holding  its  aperture 
within  the  mouth  of  the  tube  to  which  its  contents  are  to  be 
restored,  and  apply  a  little  heat;  part  of  the  liquid  will  be 
forced  out,  or  indeed  the  whole  if  it  be  volatile;  if  not,  on 
cooling,  a  bubble  of  air  will  enter,  and  a  second  and  third 
application  of  heat  will  displace  the  whole  of  the  contents. 
On  introducing  a  portion  of  water  and  displacing  it,  and 
repeating  this  two  or  three  times,  the  bulb  will  be  sufficiently 
,cleansed,  may  then  be  filled  entirely  with  water,  and  weighed 
when  cold  as  before.     The  weights  of  equal  bulks  of  the 
fluid  and  water  are  now  known,  and  the  specific  gravity 
readily  obtained  by  calculation. 

102.  Although  the  process  has  been  described  in  this 
order,  it  is  generally  better,  after  weighing  the  bulb,  to  in- 
troduce the  water  and  obtain  its  weight  first,  and  then  that 
of  the  peculiar  fluid;  for  if  an  accident  happens  in  the  water 
experiment,  and  the  bulb  is  destroyed,  it  does  not  involve  a 


-DRIED  05 

lepetition  of  the  process  with  the  valuable  liquid.  Further, 
it  is  easy  at  all  times  to  free  the  bulb  from  the  water  of  the 
first  part  of  the  process,  but  not  always  so  to  dissipate  the 
remains  of  peculiar  substances  which  may  be  decomposable 
by  heat  or  not  soluble  in  water.  The  bulb  may  be  emptied 
of  water  by  first  throwing  out  the  larger  part  as  already 
described,  then  heating  it  over  the  flame  of  a  spirit  lamp,  or 
in  hot  air,  to  convert  the  rest  of  the  moisture  into  vapour, 
and  either  retaining  it  there  some  time,  or,  if  that  be  incon- 
venient, allowing  it  to  cool,  that  the  vapour  may  condense 
and  the  air  enter.  A  second  application  of  heat,  at  the  same 
time  that  it  converts  the  remaining  water  into  steam,  throws 
out  a  portion  with  the  expelled  air;  being  cooled  and  again 
heated  a  few  times,  the  bulb  is  soon  effectually  dried.  The 
process  may  be  expedited  by  cooling  a  part  near  the  mouth 
first,  which  is  easily  done  by  touching  it  with  a  cold  sub- 
stance (1356),  and  causing  the  principle  condensation  of 
moisture  there,  and  then  also  heating  the  same  part  first;  in 
this  way  the  air  carries  out  the  water  in  fewer  operations, 
but  these  facilities  are  only  to  be  learned  and  appreciated 
by  practice.  In  all  exposures  of  the  bulb  to  heat,  in  expe- 
riments relating  to  specific  gravity,  especial  care  must  be 
taken  that  the  heat  is  not  such  as  to  soften  the  glass  after 
one  of  the  fluids  has  been  weighed,  for  in  that  case  the  form 
and  size  of  the  vessel  will  be  altered,  the  process  must  be 
recommenced,  and  the  previous  trouble  will  be  utterly  use- 
less. 

[There  is  a  great  saving  of  time  and  trouble,  by  adopting 
the  following  mode  of  obtaining  the  objects  for  which  Mr 
Faraday  suggests  the  use  of  the  glass  bulb.  Draw  out  one 
end  of  a  small  glass  tube  into  a  capillary  termination  and 
seal  that,  then  inflate  into  a  ball  a  part  of  the  tube  immedi- 
ately beyond  the  capillary  portion,  and  above  that  reduce 
the  tube  at  a  single  point  to  a  very  small  diameter. 

Finally,  to  the  open  end  attach  a  gum  elastic  bag  of  di- 
mensions rather  greater  than  those  of  the  bulb,  or  insert  a 
rod  and  piston,  and  break  off  from  the  capillary  extremity 
enough  to  leave  that  open.  By  means  of  the  gum  elastic 
bag  or  the  piston,  the  enlarged  or  bulbous  part  of  the  tube 
I 


66  HYDROMETER— CIRCUMSTANCES  AFFECTING    IT. 

is  easily  filled;  and  the  loss  sustained  by  the  vessel  from 
which  the  liquid  is  withdrawn  is  readily  appreciated.  To 
empty  it  again,  and  fill  it  with  water  or  any  other  liquid,  is 
the  work  of  a  few  moments. — Ed.] 

103.  The  specific  gravity  of  fluids. is  frequently  ascertain- 
ed by  the  hydrometer,  a  well  known  instrument,  which  is  of 
great  service  where  hasty  estimates  of  only  moderate  accu- 
racy are  required;  but  it  will  not  give  correct  or  even   uni- 
formly incorrect  results  without  attention.     The  stem,  being 

the  part  which  cuts  the  surface  of  the  liquid,  resembles  in 
that  respect  the  suspending  link  used  in  taking  the  specific 
gravity  of  solids  (87,  &c.),  and  is  liable  to  be  affected  in  a 
similar  way,  but  in  many  cases  to  a  much  greater  extent, 
because  of  its  necessary  thickness.  If  its  surface  does  not 
moisten  freely  with  the  fluid  in  which  it  floats,  it  will  be 
found  easy  upon  trial,  to  make  the  hydrometer  stand  two  or 
three  degrees,  or  more,  higher  or  lower  in  the  same  liquid; 
and  when  the  hydrometer  does  readily  become  wetted,  and  has 
even  had  the  stem  purposely  moistened,  the  same  effect  may 
be  produced,  and  that  not  in  fluids  particularly  viscid,  but  in 
water  and  aqueous  solutions: — hence  a  source  of  irregularity 
in  the  indications  of  the  instrument,  which  must  be  avoided 
as  much  as  possible.  For  this  purpose,  keep  the  hydrometer 
perfectly  clean  and  free  from  any  unctuous  or  greasy  matter, 
which  might  be  the  consequence  of  handling  it.  When 
put  into  the  fluid  it  should  be  allowed  to  sink  gradually  till 
at  rest,  and  then  be  depressed  about  an  inch  lower,  which 
will  give  it  an  ascending  power,  and  moisten  a  certain  por- 
tion of  the  stem;  the  jar  containing  the  fluid  is  to  be  tapped 
to  cause  vibration,  and  the  instrument  allowed  again  to  take 
a  statk  of  rest,  when  its  position  should  be  observed.  The 
instrument  should  then  be  raised  about  half  an  inch  out  of 
the  fluid,  and,  tapping  the  jar  as  before,  suffered  to  sink 
slowly,  and  observed  whether  it  takes  the  same  position  it 
occupied  at  first;  if  it  does,  the  observation  is  as  correct  in 
this  respect  as  it  can  be. 

104.  If  the  fluid  be  viscid,  the  liability  to  inaccuracy  in 
this   instrument   is   increased,   both  by  the  difficulty  with 


HYDllOMETEll ITS   INDICATIONS.  07 

which  it  sinks  or  rises  to  the  point  to  which  its  mere  weight 
would  carry  it,  and  also  by  the  greater  quantity  which  ad- 
heres to  the  part  of  the  stem  that,  having  been  immersed,  is 
afterwards  raised  above  the  surface.  If  the  fluid  be  turbid, 
it  is  not  the  gravity  of  the  suspending  fluid  itself  that  is  ob- 
tained, but  of  the  liquid  so  laden  with  other  matter.  Some 
precipitates  will  be  days  and  even  weeks,  before  they  will 
settle  from  the  fluid  in  which  they  are  formed,  and  yet  are  so 
heavy  as  very  materially  to  increase  the  specific  gravity  of 
the  whole;  and  M.  P.  S.  Girard  has  stated*,  that  a  peculiar 
molecular  attraction  exists  between  such  particles  in  the  fluid 
as  to  buoy  up  the  hydrometer  by  a  force,  not  merely  equal 
to  the  increased  weight,  but  considerably  surpassing  it. 
Brewers  and  other  persons  frequently  require  the  specific 
gravity  of  a  mixture  of  solid  and  fluid  matter — their  object 
being,  by  the  buoyance  of  the  hydrometer,  to  estimate  the 
former  as  well  as  the  latter;  but  if  the  effect  here  noticed 
exists,  a  source  of  error  is  introduced  of  which  they  take  no 
account,  unless,  indeed,  their  instruments  be  graduated  by 
experiment  with  fluids  similar  to  those  they  wish  afterwards 
to  examine.  It  is  probably,  however,  so  small,  as  to  be  of 
no  importance  in  their  comparatively  rough  estimates. 

105.  In  all  experiments  made  with  the  hydrometer,  anas- 
cent  of  the  fluid  will  take  place  round  the  stem,  producing 
the  elevation  before  mentioned  (8'fJ.  This  occasions  a  curve 
in  the  surface,  ann  dome  persons  read  off  the  graduation  on 
the  stem,  where  it  coincides  with  the  middle  of  this  curve — 
others  at  the  top,  and  others  again  at  the  bottom.  It  is  ne- 
cessary, for  the  sake  of  consistent  observations,  always  to 
read  off  from  the  same  part  of  the  curve;  and  if  the  instru- 
ment has  been  graduated  by  experiment,  the  divisions  being 
made  with  reference  to  the  part  of  the  curve  from  which 
they  are  afterwards  to  be  read,  it  will  so  far  be  correct.  As 
the  force  which  causes  the  elevation  tends  to  depress  the 
instrument  in  the  fluid,  observations  made  at  the  bottom  of 
the  curve  will  be  nearer  to  the  truth  than  those  made  at  the 


*  On  Liquid  Almospheic^   and  (hen    Influence  on    the  Sulit!    Particles,  they 
nvelope.— Mcmoiies  de  FAcademic  Royal?,  iv  ,  1819,  1820. 


68          •  HYDROMETER  OBSERVED VERIFIED. 

top.  But  the  curve  itself  varies,  not  merely  in  size  because 
of  differences  in  the  weight  or  specific  gravity  of  the  fluid, 
but  in  weight  also,  because  of  differences  in  the  cohesive  at- 
traction of  different  fluids. 

106.  Amongst  other  points  relative  to  the  state  of  the  flu- 
id, temperature  should  not  be  forgotten ;  constancy  in  this 
respect  being  as  important  as  in  experiments  made  with  the 
bottle.     (93—95.) 

107.  The  hydrometer,  when  first  procured,  should  be  veri- 
fied by  trial  in  solutions  of  which  the   specific   gravity  has 
been  ascertained  by  the  bottle.     It  is  not  necessary  to  make 
many  trials  of  this  kind,  its  verification  being  more   readily 
effected  in  the  following  manner.     First,  ascertain  with  two 
fluids  of  different  specific  gravities,  that  one   indication  to- 
wards each  end  of  the  scale  is  correct.     Then,  suspending 
the  hydrometer  from  the  pan  on  one  side  of  a  balance,  let  it 
descend  into  a  solution  as  light,  or  lighter  than  any  to  be 
measured  on  the  scale,  but  buoying  it  up  by  weights  in  the 
other  pan,  so  that  the  surface  of  the  fluids  shall  cut  the  scale 
at  the  lower  part.     Make  equal  additions  of  weight  in  suc- 
cession to  the  pan  from  which  the  hydrometer  is  suspended, 
and  observe  the  descent  each  time  :  if  they  are  equal,  as 
read  off  on  the  scale,  then  the  divisions  are  equal  in  bulk, 
and  the  graduation  is  correct;  if  unequal,  the  graduation  is 
incorrect,  and  would  not  correspond  with  the  results  obtain- 
ed by  the  specific  gravity  bottle.     The  more  numerous  the 
points  thus  observed,  that  is,  the  smaller  the  weight  added 
each  time,  the  more  accurate  and  close  is  the  trial*. 

108.  A  solid  glass  ball,  or  bulbs  of  glass,  are   frequently 
used  for  ascertaining  the  specific  gravity  of  fluids.     If  a  ball 
of  glass  suspended  from  the  balance  be  wholly  immersed  in 
a  liquid,  it  will  be  buoyed  up  by  a  force  equal  to  the  weight 
of  the  liquid  it  displaces,  and  seem  to  lose  weight  to  that 
amount.     By  being  immersed,  therefore,  in  succession  into 
different  liquids,  the  weights  of  equal  volumes  are  thus  ob- 
tained, for  the  ball  measures  out  the  volume  each  time,  and 

See  Moore  on  the  Graduation  of  the  Hydrometer ;  Dublin  Philosophical 
Jolirnal, 


SPECIFIC    GRAVITY    BULlib.  69 

the  specific  gravities  are  then  known.  The  precautions  here 
required  are  the  same  as  those  belonging  to  the  experiments 
on  the  specific  gravity  of  solid  bodies.  (81 — 88.) 

109.  Sometimes  several  hollow  bulbs  of  different  specific 
gravities  are  used;  those   which  are  too   heavy  sinking,  and 
those  which  are  too  light  floating.     The.  proper  strength  of 
some  solutions  evaporated  in  the  large  way  is  thus  estimat- 
ed.    Sea- water  for   instance,  in  salt-works,  is  concentrated 
by  exposure  to  air,  until  it  has  such  a  specific  gravity,  that, 
of  two  previously-arranged  glass  bulbs,  one  will  sink  and  the 
other  swim.     Their  use  in  chemical  research  is  rare;  but  an 
excellent  instance  of  the  delicacy  with  which  the   principle 
may  in  some  cases  be  applied,  as  also  a  specimen  of  useful 
manipulation,  may  be  found  in   Mr  Crichton's  paper  on  the 
maximum  density  of  water*. 

110.  Another  instance  of  the  application  of  similar  bulbs 
to  the  determination  of  specific  gravity,  when  no  other  means 
were  available,  occurs  with  respect  to  the  liquids  produced 
by  the  condensation  of  gasesf.     The  bulbs  used  were  very 
small,  and  made  as  hereafter  to  be  described  (1 199).     Their 
specific  gravities  were  ascertained  by  putting  them  into  dif- 
ferent solutions  of  known  specific  gravity,  and   the  bulbs, 
thus  prepared,  were  introduced  into  the  vessels  in  which  the 
gases  were  to  be  liberated  or  condensed.     When   surround- 
ed by  the  fluid,  its  density  was  in  some  degree  judged  of  by 
the  sinking  or  swimming  of  the  included  bulb,  and  then  by 
successive  trials  with  heavier  or  lighter  bulbs,  more   accu- 
rately ascertained. 

111.  Substitutes  for  a  balance,  though  not  often  required, 
are,  in  particular  situations,  very  valuable,  and  there  are  few 
philosophic  travellers  who  have  not  felt  this  want.     Mr  Be- 
van  recommends  for  this  purpose  a  strung  bowj,  which,  if 
not  at  hand,  may  generally  be  made  out  of  a  piece  of  whale- 
bone, a  stick,  or  other  substance,  and  which,  being  suspend- 
ed by  the  middle  of  the   bow,  is   to  have   the   body  to   be 

*  Annals  ol  Philosophy,  New  Seiic.-,  v.  401.  ir 

t  Philosophical  Transactions,  1823,  p.  191, 
I  Technical  Repository,  vi.  196. 


70  SUBSTITUTES  FOR  THE  BALANCE. 

weighed  attached  to  the  middle  of  the  string.  The  flex- 
ure occasioned  by  it  is  to  be  observed,  which  will  best  be 
done  by  marking  the  point  to  which  that  part  of  the  string 
from  which  the  body  hangs,  descends:  then  removing  the 
substance  and  replacing  it  by  weights,  sufficient  are  to  be 
used  to  cause  the  same  flexure,  and  thus  the  weight  of  the 
substance  will  be  obtained.  An  elastic  beam,  stick,  or  other 
body,  firmly  fixed  at  one  end,  and  loaded  at  the  other  with 
the  substance  and  the  weights  in  succession,  will  answer  the 
same  purpose ;  and  the  means  of  making  a  temporary  scale- 
pan,  to  receive  the  substance  and  the  weights,  and  a  gradu- 
ation to  measure  its  descent,  are  so  simple  and  evident  as  not 
to  require  description. 

112.  The  following  account  of  a  very  delicate  and  easily 
constructed  balance  is  from  a  letter  written  by  Dr  Black  to 
Mr  Smithson*,  and  is  a  valuable  piece  of  information  to  those 
who,  having  occasion  for,  are  deprived  of  the  use  of,  a  good 
balance.  '  The  apparatus  I  use  for  weighing  small  globules 
of  metal,  or  the  like,  is  as  follows  :  a  thin  piece  of  fir-wood, 
not  thicker  than  a  shilling,  and  a  foot  long,  0.3  of  an  inch 
broad  in  the  middle,  and  0.15  of  an  inch  at  each  end,  is  di- 
vided by  transverse  lines  into  20  parts,  that  is  10  parts  on 
each  side  of  the  middle.  These  are  the  principal  divisions, 
and  each  of  them  is  subdivided  into  halves  and  quarters. 
Across  the  middle  is  fixed  one  of  the  smallest  needles  I  could 
procure,  to  serve  as  an  axis,  and  it  is  fitted  in  its  place  by 
means  of  a  little  sealing-wax.  The  numeration  of  the  divi- 
sions is  from  the  middle  to  each  end  of  the  beam.  The  ful- 
crum is  a  bit  of  brass  plate,  the  middle  of  which  lies  flat  on 
my  table  when  I  use  the  balance,  and  the  two  ends  are  bent 
up  to  a  right  angle  so  as  to  stand  upright.  These  two  ends 
are  ground  at  the  same  time  on  a  flat  hone,  that  the  extreme 
surfaces  of  them  may  be  in  the  same  place ;  and  their  dis- 
tance is  such  that  the  needle,  when  laid  across  them,  rests  on 
them  at  a  small  distance  from  the  sides  of  the  beam.  They 
rise  above  the  surface  of  the  table  only  l-i  or  2-10ths  of  an 
inch,  so  that  the  beam  is  very  limited  in.  its  play-  The 

*  Annals  of  Philosophy,  New  Series,  x,  52. 


BLACK'S  DELICATE  BALANCE,  71 




weights  I  use  are  one  globule  of  gold  which  weighs  one 
grain,  and  two  or  three  others  which  weigh  one  tenth  of  a 
grain  each ;  and  also  a  number  of  small  rings  of  fine  brass 
wire,  made  in  the  manner  first  mentioned  by  Mr  Lewis,  by 
appending  a  weight  to  the  wire,  and  coiling  it  with  the  ten- 
sion of  that  weight  round  a  thicker  brass  wire  in  a  close 
spiral,  after  which  the  extremity  of  the  spiral  being  tied  hard 
with  waxed  thread,  I  put  the  covered  wire  in  a  vice,  and  ap- 
plying a  sharp  knife,  which  is  struck  with  a  hammer,  I  cut 
through  a  great  number  of  the  coils  at  one  stroke,  and  find 
them  as  exactly  equal  to  one  another  as  can  be  desired. 
Those  I  use  happen  to  be  the  one-thirtieth  part  of  a  grain 
each,  or  300  of  them  weigh  10  grains,  but  I  have  others 
much  lighter. 

i  You  will  perceive  that,  by  means  of  these  weights  placed 
on  different  parts  of  the  beam,  I  can  learn  the  weight  of  any 
little  mass,  from  one  grain  or  a  little  more  to  the  y^F  °f  a 
grain.  For  if  the  thing  to  be  weighed  weighs  one  grain,  it 
will,  when  placed  on  one  extremity  of  the  beam,  counter- 
poise the  large  gold  weight  at  the  other  extremity; — if  it 
weigh  half  a  grain,  it  will  counterpoise  the  heavy  gold  weight 
placed  at  5  ; — if  it  weigh  0.6  of  a  grain,  you  must  place  the 
heavy  gold  weight  at  5,  and  one  of  the  lighter  ones  at  the 
extremity  to  counterpoise  it;  and  if  it  weighs  only  one,  or 
two,  or  three,  or  four-hundredths  of  a  grain,  it  will  be  coun- 
terpoised by  one  of  the  small  gold  weights  placed  at  the 
first,  or  second,  or  third,  or  fourth  division ; — if,  on  the  con- 
trary, it  weigh  one  grain  and  a  fraction,  it  will  be  counter- 
poised by  the  heavy  gold  weight  at  the  extremity,  and  one 
or  more  of  the  lighter  ones  placed  on  some  other  part  of  the 
beam. 

'This  beam  has  served  me  hitherto  for  every  purpose; 
but  had  I  occasion  for  a  more  delicate  one,  I  could  make  it 
easily  by  taking  a  much  thinner  and  lighter  slip  of  wood, 
and  grinding  the  needle  to  give  it  an  edge.  It  would  also 
be  easy  to  make  it  carry  small  scales  of  paper  for  particular 


RITCHIES  BALANCE. 

purposes;'  the  fulcrum  being  then  placed  on  a  stool  or  any 
other  support  that  is  horizontal,  raised,  and  narrow. 

113.  Mr  Ritchie  has  also  contrived  a  very  cheap  and  deli- 
cate balance.     It  consists  of  a  slender  beam  of  wood,  about 
18  or  24  inches  long,  tapering  a  little  from  the  middle  to 
each  end.    A  fulcrum  of  tempered  steel,  resembling  the  blade 
of  a  penknife,  is  made  to  pass  through  the  middle  of  the 
beam  a  little  above  the  centre  of  gravity.     Similar  steel 
blades  are  also  made  to  pass  through  the  ends  of  the  beam 
for  suspending  the  scales.     The  fulcrum  rests  on  two  small 
portions  of  thermometer  tube,  fixed  horizontally  on  an   up- 
right wooden  support,  held  firmly  by  a  foot;  the  support  has 
a  slit  passing  along  the  middle,  to  allow  the  indicating  nee- 
dle attached  to  the  beam  beneath  the  centre  of  gravity  to 
play  freely  between  the  sides.     A  small  scale  made  of  card, 
and  divided  into  any  number  of  equal  parts,  is  placed  on  the 
support  for  the  purpose  of  ascertaining  the  point  at  which 
the  needle  becomes  stationary.     This  balance,  Mr  Ritchie 
says,  possesses  extreme  delicacy,  and  may  be  made  even 
more  sensible  than  that  belonging  to  the  Royal  Society  of 
London. 

The  equality  of  the  two  ends  is  not  a  necessary  consider- 
ation, according  to  the  method  of  double  weighing  referred 
to  before,  and  invented  by  Borda.  To  weigh  with  the  bal- 
ance, let  the  body  be  placed  in  one  of  the  scales,  and  bring 
the  indicating  needle  to  any  point  by  small  shot  placed  in 
the  other  scale,  remove  the  body  and  replace  it  by  as  many 
known  weights  as  will  bring  the  needle  to  the  former  posi- 
tion. These  weights  give  the  weight  of  the  body*. 

114.  In  weighing  with  these  balances,  or  generally  with 
such  as  are  a  little  out  of  order,  the  weights  should  be  ap- 
plied and  ascertained  on  the  same  side  with  the  substance, 
that  irregularities  of  action  may  be  avoided  as  much  as  pos- 
sible.    Thus,  the  substance  to  be  weighed  should   be  put 
into  one  pan,  and  counterpoised  by  any  convenient  thing,  as 
sand,  in  the  other;  after  which,  removing  the  substance,  its 
place  is  to  be  supplied  by  weights,  until  an  exactly  equal 

*  Biewster's  Journal,  v.  118, 


INACCURATE  BALANCES WEIGHTS.  73 

effect  is  produced,  when  of  course  the  amount  of  the  weights 
used  will  be  the  weight  of  the  substance.  Or  if  a  given 
quantity  be  wanted,  first  counterpoise  the  weight,  and  after- 
wards replace  it  by  the  substance  to  be  weighed.  Inequal- 
ity in  the  arms  is  thus  compensated 

115.  Substitutes  for  weights,  should  they  ever  be  required, 
may  be  made  by  means  of  a  balance  in  one  or  two  ways. 
Pieces  of  metal  or  other  convenient  substances  may  be  ad- 
justed to  have  equal,  double,  triple,  or  any  other  proportion 
of  weight,  to  a  standard  piece,  and,  being  used  as  weights 
at  the  time,   will  give   proportionate  results  ;  or  if  results 
comparable  with  other  weights  are  required,  their  value  may 
be  estimated  by  actual  comparison  at  a  future  convenient 
opportunity.     Such  regular  weights,  of  considerable  accu- 
racy, are  easily  obtained,   by   cutting  off  equal  or  given 
lengths  of  a  copper  wire,  the  wire  being  of  such  thickness 
that  at  least  half  an  inch  in  length  may  be  allowed  for  the 
smallest  weight ;  its  uniform  thickness  should  be  ascertained 
by  trying  the  first  and  the  last  weight  cut  off  against  each 
other.      Occasionally  the  products  obtained  from  experi- 
ments may  be  balanced  by  pieces  of  lead,  which  are  to  be 
weighed  when  an  opportunity  occurs,  and  the  results  nume- 
rically estimated. 

116.  A  method  of  making  small  weights  has  been  already 
described  in  Dr  Black's  letter  (112),  but  Mr  Smithson  finds 
it  preferable,  first  to  ascertain  the  weight  of  a  certain  length 
of  wire,  and  then  to  take  that  portion  of  it  which  may  suf- 
fice for  the  weight  wanted.     If  fine  wire  is  employed,  a  set 
of  small  weights  may  be  thus  made  with  great  accuracy  and 
ease.     Inconvenience  from  the  length  of  the  wire  in  the 
higher  weights  :s  obviated  by  rolling  it  round  a  cylindrical 
body  into  a  ring,  and  twisting  this  to  a  cord*. 

117.  The  following  relative   table  of  different  weights 
will  be  frequently  used  in  the  laboratory. 

Grains. 

Pound  avoirdupoise 7000 

Ounce  avoirdupoise     ....    437.5 

*  Annals  of  Philosophy,  New  Series,  x.  53. 

K 


74  LABORATORY  MEASURES. 

Grains. 

Pound  troy    .     .     f    .  v^^^«  6760 
Ounce  troy    .     .    I     .  jfc    •     480 

Gramme 15.4063 

Decigramme 1.5406 

Centigramme 0.1540 

Milligramme      ./ 0.0154 


SECTION  III. 
MEASURES— MEASURING. 

118.  ORDINARY  laboratory  service  requires  no  other  mea- 
sures than  such  as  are  fitted  to  ascertain  the  bulk  of  liquids 
or  gases.  Hence  two  integers  are  abundantly  sufficient, 
the  pint  and  the  cubic  inch.  The  pint  measures  may  be 
such  as  are  furnished  in  commerce,  either  conical,  cylindri- 
cal, or  of  any  other  form,  and  of  glass,  and  graduated  :  but 
they  should  always  be  verified  before  they  are  permitted  to 
pass  into  use.  Where  the  same  measure  is  used  for  large 
as  well  as  small  quantities,  those  which  are  conical  have  an 
advantage  in  the  smaller  divisions  over  such  as  are  cylindri- 
cal, the  surfaces  of  small  quantities  being  less,  and  conse- 
quently the  bulks  more  accurately  determined ;  but  it  is 
belter  to  have  two  or  three  measures  of  different  sizes, 
varying  in  diameter,  for  different  quantities.  The  wine 
pint  measure  has  been  usually  divided  into  sixteen  parts, 
each  being  called  a  fluid  ounce,  and  liquid?  are  frequently 
measured  by  these  ounce  volumes,  which  in  such  bulk 
weighed  more  or  less  than  an  ounce.  The  standard  or  im- 
perial pint  now  to  be  used  is  larger  than  tne  wine  pint,  in 
the  ratio  of  6:  5  (154).  It  is  to  be  divided  into  twenty 
parts,  to  be  called  fluid  ounces ;  these  will  not  be  the  same 
exactly  with  the  former  fluid  ounces,  but  will  have  the  great 
advantage,  when  estimated  with  distilled  water,  of  weighing 
an  exact  ounce  avoirdupoise.  The  measure  should  be 
graduated  in  two  places  on  opposite  sides,  that  when  the 


MEASURES   GRADUATED USED.  75 

volume  of  a  fluid  is  to  be  determined,  its  surface  may, 
for  greater  accuracy,  be  observed  by  both  gradua- 
tions. A  pint,  a  half  pint,  and  a  quarter  pint  mea- 
sure, of  the  form  and  relative  dimensions  as  to  height 
and  diameter  of  the  one  figured  in  the  wood-cut, 
should  be  in  the  laboratory.  It  is  also  useful  to 
have  a  graduation  on  the  vessels  in  cubic  inches, 
this  being  done  on  both  sides  at  equal  distances 
from  the  former  graduations. 

119.  These  measures  should  be  graduated  according  to 
the  late  parliamentary  standard,  by  which  the  pint  is  ascer- 
tained to  consist  of  8750  grains  of  water  at  62°  Fahrenheit, 
barometer  at  30  inches ;  and   the    cubic  inch  of  252.458 
grains  of  water,  at  the  same    temperature  and   pressure. 
They  are  verified  by  being  counterpoised  (64),  and  having 
these  quantities  of  water,  or  their  multiples,  or  divisions, 
weighed  into  them,  and  the  coincidence  of  the  surface  of 
the  liquid  and  its  corresponding  mark  noted.     If  they  do 
not  agree,  a  slight  scratch  should  be  made  with  a  diamond 
or  file,  at  the  place  where  the  mark  ought  to  be  (132). 

120.  Preparatory  to  the  use  of  these  vessels,  one  particular 
place  upon  a  table  or  shelf  should  be  selected,  which  is  flat, 
firm,  and  which  should  generally  be  kept  clear  of  other  things 
for  this  purpose  alone.     The  measure,  when  placed  upon  it, 
should  stand  steady  and  perfectly  upright.     In  the  verifica- 
tion, it  will  be  necessary  to  observe,  that  when  the  measure 
containing  the  weighed  quantity  of  water  is  placed  in  this 
situation,  the  surface  of  the  fluid  should  coincide  both  with 
the  graduation  on  the  near,  and  also  on  the  farther  side : 
this  is  best  seen  by  bringing  the  eye  to  a  level  with  the 
surface ;  and  still  further  security  is  gained  as  to  the  right 
position  of  the  measure,  if  the  water  stand  at  equal  heights 
on  the  lateral  graduations  of  the  denomination  not  immedi- 
ately in  use.     In  measuring  at  any  future  time,  similar  pre- 
cautions should  be  observed,  and  these  will  require  atten- 
tion the  more  imperatively,  if  from  any  circumstance  one 
particular  spot  is  not  selected,  as  above  advised,  but,  on  the 
contrary,  any  part  of  the  table  used. 


76  GLOBULAR  MEASURES. 

121.  With  liquids  which  moisten  the  glass,  an  elevation 
of  the  fluid  round  its  surface  in  contact  with  the  vessel  will 
take  place.     The  measurement,  except  in  minute  vessels, 
will  be  most  accurately  made,  if  taken  from  the  general  sur- 
face of  the  fluid,  and  not  from   the  middle  or  top  of  the 
elevation  (769);  but  it  is  essentially  necessary  that  it  be 
always  made  in  the  same  way  as  that  adopted  in  the  verifi- 
cation of  the  measures.     With   mercury  there    will  be  a 
depression  round  the  glass  instead  of  an  elevation,  except 
in  particular  circumstances.      It  is  here  again  most  cor- 
rect to  make  the  estimate  from  the  general  surface  of  the 
fluid. 

122.  When  very  accurate  measurement  is  desirable,  as  in 
the  analysis  of  a  mineral  water,  it  is  better  to  perform  it  in  a 

globular  vessel  having  a  glass  neck,  and  of  such 
capacity   as  to  be  filled  partly  up  the  neck  by  a 
weighed  pint  or  half  pint  of  water  at  62° ;  the  exact 
place  being  then  marked  with  a  diamond  or  file. 
So  little  surface  is  left  at  the  place  where  the  bulk 
is  estimated,  that  scarcely  any  variation  can  occur 
in  that  respect ;  and  if  the  measurements  be  made  at  a  con- 
stant temperature,  they  are  very  accurate.     Two  such  mea- 
sures, a  pint  and  a  half  pint,  will  be  sufficient.     Small  quan- 
tities are  generally  more  accurately  determined  by  weight 
than  by  measure. 

123.  Three  jugs,  of  half  a  pint,  a  pint,  and  a  quart,  will 
be  found  of  great  service  for  ordinary  use. 

124.  The  cubic  inch,  with  its  divisions  and  multiples,  is 
Used  both  for  liquids  and  gases.     For  exclusive  liquid  use, 
the  cubic  inch  graduation  on  the  vessels  already  mentioned 
will  suffice ;  those  to  be  described  will  serve  generally  for 
both  forms  of  matter. 

125.  Bottles  are  sold  by  the  instrument  makers,  which 
contain  an  exact  cubic  inch  when  the  stopper  is  put  into 
its  place.      Tubes  also  of  similar  capacity,  and  supplied 
with  a  ground  stopper,  are  manufactured  with  a  graduation 


CUBIC  INCH  MEASURES — THEIR  VARIETY, 


77 


on  the  side,  by  which  the  subdivision  is  car- 
ried to  tenths  and  twentieths,  and  even  farther 
if  necessary.  Whether  these  are  in  the  la- 
boratory or  not,  there  should  be,  at  all  events, 
a  few  jars  and  tubes  accurately  graduated 
into  cubic  inches,  tenths,  and  hundredths  ; 
one  jar  may  be  about  two  inches  in  diame- 
ter and  six  inches  high  ;  another  about  an 
inch  in  diameter,  and  of  the  same  height ;  a 
third,  which  will  be  almost  a  tube,  half  an 
inch  in  diameter,  and  eight  or  nine  inches 
long  ;  and  a  fourth  of  the  same  length,  but 
still  smaller.  These  should  be  moderately 
thick, soas,  when  filled  with  mercury,  to  bear 
the  weight  of  that  metal,  and  sustain  labora- 
tory use,  without  great  risk  of  breaking:  they 
should  be  ground  at  the  ends,  so  as  to  be  closed  accurately 
by  a  flat  piece  of  glass  (1348).  It  will  be  sufficient  that 
the  smaller  vessels  be  graduated  on  one  side  only,  but  it  is 
better  that,  when  the  diameter  is  an  inch  and  a  half  or  more, 
they  should  be  graduated  upon  opposite  sides,  for  the  pur- 
pose of  observing  more  accurately,  as  before  explained  (120). 

126.  All  these  measures  should  be  verified  by  weighing 
into  them  successive  portions  of  water  or  mercury.     A  cubic 
inch  of  water  at  62°  weighs,  as  before  mentioned,  252.458 
grains,  and  a  cubic  inch  of  mercury  at  the  same  tempera- 
ture, 3425.35  grains*.     Water  is  very  convenient  for  the 
estimation  down  to  the  cubic  inch,  and  some  divisions  below 
it;  but  for  the  tenths,  and  especially  the  hundredths,  mer- 
cury is  far  more  exact  and  expeditious. 

127.  It  is  frequently  necessary  to  graduate  vessels,  and 
especially  tubes,  in  the  laboratory.     The  general  method  of 
doing  this  will  be  easily  understood  from  what  has  been  said 

*  This  assumes  the  specific  gravity  of  mercury  as  13.568,  which  is  what  I  find 
pure  mercury  to  possess  at  62°  Fahrenheit.  Sir  H.  Davy  makes  it  heavier.  Of 
course  any  metal  likely  to  enter  as  impurity  into  mercury  would  render  it 
lighter. 


78  GRADUATION  OF  VESSELS OF  TUBES. 

with  regard  to  the  verification  of  measures  bought  of  the 
maker ;  but  there  are  some  facilities  in  the  practice  which 
will  require  description.  Tubes  are  generally  in  use  for  the 
measurement  of  gas  at  the  mercurial  trough,  and  should  be 
several  in  number,  and  of  different  diameters,  to  afford  op- 
portunity for  a  graduation  more  or  less  minute.  The  labo- 
ratory is  but  poorly  stocked  that  has  not  a  dozen  of  them. 
They  should  not  be  less  than  the  one-fifteenth  of  an  inch  in 
thickness  when  of  a  diameter  smaller  than  half  an  inch,  and 
thicker  if  wider.  The  closed  ends  should  be  of  equal  thick- 
ness with  the  sides,  and  should  be  round,  not  pointed. 

128.  The  marks  on  vessels  graduated  by  the  instrument- 
maker  are  cut  by  the   glass-grinder's   wheel,  but  in    the 
laboratory  they  are  made  with  simpler  instruments.     A  gun- 
flint  is  convenient  for  scratching  on  the  surface  of  glass. 
Fragments  of  diamond  are  also  set  in  handles  for  the  same 
purpose  ;  they  are  not  intended  to  cut,  but  merely  to  abrade 
or  roughen  the  surface,  and  are  called  scratching  or  writing 
diamonds  (974).     Small  three-square  files,  about  half  an 
inch  wide  on  each  side,  are  so  useful  in  the  laboratory  for 
marking  on  convex  surfaces  of  glass  or  for  cutting  tubes 
(1152),  that  they  cannot  be  dispensed  with. 

129.  Having  selected  the  tube,  first  draw  a  line  upon  it 
from  top  to  bottom.     This  is  easily  done  by  laying  the  tube 
upon  the  table,  against  the  edge  of  a  flat  slip  of  wood  or  a 
ruler,  and  drawing  either  the  flint  or  scratching  diamond 
down  it  where  it  rests  against  the  ruler,  bearing  as  it  were 
into  the  angle  formed  by  the  ruler  and  the  surface  of  the 
tube.     The  line  should  not  be  broad  and  rough,  but  regu- 
lar, neat,  and  straight.     The  tube  is  now  to  be  balanced  by 
a  counterpoise  (64),  and  is  then  ready  to  receive  the  suc- 
cessive portions  of  mercury,  by  which  equal  given  volumes 
are  to  be  measured  out,  and  to  have  them  marked  off  by 
small  lines  across  the  long  one  first  drawn.     Suppose  the 
hundredths  of  a  cubical  inch  are  to  be  marked  down,  the 
tube   being   about  2-10ths  of  an  inch  internal  diameter : 
34.25  grains  of  mercury,  which  at  62°  Fahrenheit  are  equal 
in  bulk  to  the  one-hundredth  of  a  cubical  inch,  are  to  be 


GRADUATION  OF  A  TUBE  BY  WEIGHING.  79 

weighed  into  it ;  the  tube  is  to  be  marked  at  the  level  of 
the  mercury,  another  34.25  grains  of  metal  is  to  be  weighed 
in,  and  its  place  marked  on  the  scale,  and  the  operation  so 
carried  on  until  the  graduation  is  finished. 

130.  But  easy  as  this  is  in  description,  it  is  otherwise  in 
practice,  without  the  aid  of  certain  facilities.     If  the  mer- 
cury be  added  without  care,  either  too  much  or  too  little 
will  be  introduced  ;  and  when   the   adjustment   is  nearly 
complete,  scarcely  little  enough  can    be   given  or  taken 
away,  owing  to  the  density  and  cohesion  of  the  metal. 

Prepare,  therefore,  a  tube  like  the 
one  represented  in  the  drawing(1181), 
about  half  an  inch  in  diameter,  four 
inches  long,  cut  level  at  one  end,  so  as  to  be  closed  by  the 
finger  if  required,  and  drawn  off  laterally  to  a  capillary 
opening  at  the  other.  If  mercury  be  poured  into  such  a  tube, 
it  will  not  flow  out  at  the  capillary  opening  whilst  the  posi- 
tion is  such  as  in  the  figure,  and  this  is  easily  given  to  it  on 
the  table  by  resting  it  on  a  list  ring  (68).  But  when  ele- 
vated sufficiently,  the  pressure  of  the  column  of  metal  will 
cause  it  to  flow  out,  and  either  in  a  continuous  stream  or  in 
minute  successive  drops,  according  to  the  degree  of  inclina- 
tion :  a  still  greater  command  over  the  flow  of  metal  is 
obtained  by  applying  the  finger  to  the  upper  extremity,  and 
thus  relieving  the  metal  from  the  pressure  of  the  atmosphere 
upon  its  upper  surface  to  a  greater  or  smaller  degree,  as 
may  be  required.  It  is  easy  in  this  way  to  supply  more  or 
less  of  the  metal  at  pleasure. 

131.  When  therefore  34.25  grains  of  mercury  are  wanted 
in  the  tube,  place  the  latter  in  one  pan,  and  weight  amount- 
ing to  34.25  grains  in  the  other;  then,  introducing  the  ca- 
pillary extremity  of  the  mercury  feeding-tube  into  the  mouth 
of  the  balanced  tube,  allow  metal  to  flow  in,  moderating  its 
addition  as  the  balance  approaches  equilibrium,  ultimately 
adding  it  only  in  minute  drops.     In  this  way  the  weight 
required  is  nearly  attained  in  a  very  short  time.     Have  it 
rather  a  little  over  than  under  weight,  and,  relinquishing 
the  feeding  vessel,  proceed  to  adjust  the  portion  in  the  tube 
to  be  graduated.     For  this  purpose,  close  its  aperture  with 


80  ADJUSTMENT MARKING  ON  GLASS. 

the  fore  finger  of  the  right  hand,  invert  the  tube  and  its 
contents,  which  will  of  course  cause  the  mercury  to  rest 
partly  on  the  finger,  and  then,  by  slightly  relaxing  the  fin- 
ger, let  a  little  drop  squeeze  out  beneath  the  edge  of  the 
glass  into  the  palm  of  the  left  hand,  where  it  is  to  be  pre- 
served. Restore  the  tube  to  its  right  position,  and  place  it 
in  the  balance ;  if  too  heavy,  put  the  first  drop  of  mercury 
out  of  the  hand  as  useless,  and  take  a  second  drop  from  the 
tube  as  before.  In  this  way  it  will  ultimately  be  obtain- 
ed too  light,  but  only  by  a  part  of  the  minute  drop  in  the 
hand.  Break  this  drop  into  several  spherules  by  pressing 
upon  it  with  the  finger,  and  take  one,  two,  three,  or  more 
of  them  into  the  tube,  by  pressing  the  edge  of  the  glass 
against  the  palm  just  beneath  the  drops,  when  they  will 
roll  in ;  observing  each  time  whether  the  mercury  in  the 
tube  balances  the  weight.  In  this  way  accurate  adjustment 
may  be  obtained  in  a  portion  of  time  not  exceeding  a  fourth 
part  of  that  required  to  read  this  description. 

132.  Tfye  next  object  is  to  mark  the  volume  occupied  by 
the  mercury,  that  being  exactly  the  one-hundredth  of  a 
cubical  inch.  The  mark  will  be  best  made  with  a  three- 
square  or  flat  file  ;  and  it  will  be  found  much  easier  to  com- 
mence it  from  the  cross  line  running  up  and  down  the  tube, 
than  from  an  unbroken  surface.  To  make  a  fair  mark  re- 
quires a  steady  pressure  on  the  file,  and  then  motion  to  a 
slight  extent.  The  feel  will  indicate  whether  a  mark  has 
been  made,  but  the  learner  should  practice  first  on  a  piece 
of  waste  glass  tube,  commencing  both  from  an  unabraded 
surface  and  from  a  cross  line ;  and  by  making  a  mere  spot, 
or  marking  a  line  of  half  an  inch  in  length.  He  will  in  this 
way  learn  in  half  an  hour  to  appreciate  by  the  feel,  the  kind 
and  the  extent  of  mark  he  makes.  He  should  also  practise 
marking  upon  any  desired  spot.  For  this  purpose  the  tube 
should  be  held  in  the  left  hand,  with  the  thumb  close  upon 
the  spot  to  be  marked ;  then  placing  the  edge  of  the  file 
upon  the  particular  place,  and  supporting  the  pressure  at 
the  same  time  by  the  thumb  at  its  side,  the  slightest  possible 
motion,  sufficient  to  break  the  surface,  should  be  given.  If 
the  commencement  be  exactly  in  the  right  place,  there  is 


MARKING   ON  THE   TUBE. 


SI 


no  difficulty  in  continuing  it,  the  file,  when  its  motion  is  re- 
newed, catching  the  previously  roughened  part;  if  the  com- 
mencement be  in  the  wrong  place,  another  trial  must  be 
made  :  the  practice  of  making  the  mark  where  desired  will 
soon  be  acquired. 

133.  This  point  attained,  the  next  thing  to  be  done  is  to 
mark  the  tube  so  as  to  record  permanently  the  volume  occu- 
pied by  the  mercury.  For  this  purpose  it  must  be  placed  in 
a  steady  upright  position;  and  though  this  may  be  effected 
sufficiently  well  with  very  small  tubes  by  holding  them  firmly 
in  the  hand,  yet  it  is  an  incorrect  method  with  larger  ones. 
Choose  therefore  a  flat  place  on  the  wall,  in  aconvenient  situa- 
tion, and  at  the  height  of  the  eye.  From  a  line  level  with  the 
eye,  and  about  two  or  three  inches  downward,  and  for  a  width 
of  five  or  six  inches,  blacken  the  wall, 
either  by  pigment  or  attaching  a  piece  of 
black  paper  to  it.  Then  firmly  fix  a  piece 
of  wood  planed  smooth  and  true,  about 
the  third  of  an  inch  thick,  an  inch  wide, 
and  six  inches  in  length,  to  the  wall  in  an 
upright  position,  across  the  middle  of  the 
blackened  part,  so  that  half  its  length 
shall  be  on  the  white  part  above.  Two  upright  re-entering 
angles  are  in  this  way  produced,  against  which  the  tubes 
may  be  firmly  held,  and  the  necessary  position  thus  effectu- 
ally obtained.  The  black  and  white  surfaces  behind  will 
each  be  found  advantageous  in  turn,  for  showing  the  coinci- 
dence of  the  surface  of  the  mercury  with  any  particular  part 
of  the  glass,  according  to  the  light  and  other  circumstances; 
and  by  shifting  the  tube  a  little  up  or  down,  the  part  where 
the  mercury  stands  may  be  placed  on  one  or  the  other  at 
pleasure,  and  yet  the  eye  be  brought  to  the  same  horizontal 
line  with  it  without  any  difficulty.  By  this  means  the  position 
of  the  tube,  of  whatever  size  it  may  be  less  than  an  inch,  is 
securely  obtained,  use  being  made  of  the  angle  on  either  side 
of  the  lath.  An  advantage  sometimes  results  from  using  a 
piece  of  lath  planed  obliquely,  so  as  to  be  thicker  at  one  edge 
than  the  other  ;  large  tubes  being  applied  to  the  deep  angle  on 

L 


82  SURFACE  OF  MERCURY  OBSERVED. 

one  side,  and  small  tubes  to  the  shallower  angle  on  the  other. 
Sometimes  an  angle  previously  existing  on  the  walls  of  the 
laboratory,  as  that  formed  by  a  bead,  may  be  used  for  these 
purposes. 

134.  The  tube  when  held  in  the  angle  may  easily  be  mark- 
ed as  before  mentioned,  by  laying  the  three-square  file  horizon- 
tally across  it  upon  the  perpendicular  line  previously  drawn, 
and  abrading   the  surface  by  a  little  motion  and  pressure. 
The  first  mark  is  merely  to  be  a  slight  extension  of  the  rough 
surface  on  the  side  of  the  line;  a  mere  spot,  which,  if  wrong, 
may  be  neglected,  and  another  made;  if  right,  may  afterwards 
be  lengthened  into  a  line.   There  is  no  necessity  for  retaining 
the  tube  against  the  wall  whilst  the  division  is  being  fully 
marked;  if  the  commencement  be  correct,  the  tube  may  be 
taken  down,  and  the  line  completed  in  any  other  position  that 
may  be  convenient. 

135.  But  there  is  yet  another  point  to  be  considered  before 
we  can  proceed  thus  far.     Mercury,  when  contained  in  glass 
vessels,  is,  in  consequence  of  its  cohesive  attraction,  depressed 
at  that  part  of  its  surface  where  it  verges  towards  the  sides  of 
the  vessel;  the  place  of  contact  with  the  glass  is  thus  rendered 
lower  than  the  general  surface,  and  consequently  asmall  space 
beneath  that  level  remains  unfilled  by  the  metal.     Hence  a 
mark  made  to  correspond  with  that  surface  would  include  a 
space  in  the  vessel  rather  larger  than  that  occupied   by  the 
metal ;  and  though  in  wide  vessels  or  tubes  the  error  thus 
introduced  is  minute,  it  is  not  so  in  tubes  of  small  diameter, 
and  frequently  amounts  to  one  of  the  divisions  marked  upon 
them.     When  to  this  is  added   the  consideration   that  the 
convexity  of  the  mercury,  in   graduating  a  tube,  is   the   re- 
verse of  that  which  occurs  when  using  the  same   tube  over 
mercury  to  measure  gas  (798),  it  is  evident  that  always  read- 
ing off  from  the  top  or  bottom  of  the  curve  would   but   in- 
crease the  errors  in  this  case  ;  and  that  with  small  quantities 
of  gas,  and  in  delicate  experiments,  they  would  become  very 
serious.     To    these    may   be    added  another  circumstance, 
which  complicates  the  errors  still  further,  namely,  that  when 
the  tubes  are  used  with   or  over  water,  the  convexity  is  t.he 


GIVING  A  FLAT  SURFACE  TO  MERCURT.  83 

reverse  of  that  with  mercury,  and  the  correction  required  con- 
sequently of  a  contrary  kind. 

136.  With  reference  to  the  process  of  graduation,  the  diffi- 
culty thus  introduced  may  be  avoided  by  using  mercury 
which  is  not  quite  clean,  but  which,  from  containing  a  little 
of  some  other  metal,  as  tin,  lead,  &c.,  has  a  film  formed  up- 
on its  surface.  The  mercury  of  the  pneumatic  trough,  if  in 
much  use,  is  generally  of  this  kind,  or  a  small  quantity  can 
be  readily  made  so  for  the  purpose,  by  adding  one  grain  of 
lead  to  four  or  five  thousand  grains  of  the  fluid  metal,  that 
quantity  being  quite  sufficient.  When  such  mercury  is  put 
into  a  tube,  a  slight  tremor  given  to  it  extends  the  film  and 
allows  the  metal  to  flow  beneath,  so  as  to  acquire  a  flat  sur- 
face instead  of  a  round  one,  and  then  the  volume  may  be  ac- 
curately marked  off  by  a  line  upon  the  glass  coinciding  with 
that  surface  (138).  Care  is  to  be  taken  that  the  mercury 
used  be  not  excessively  foul,  or  so  dusty  as  to  throw  up  a 
thick  coat  of  film  to  its  surface,  since  no  indication  of  vol- 
ume belonging  to  a  given  weight  of  mercury  would  then  be 
obtained. 

137.  No  further  difficulty  will  now  arise   in  the  way  of 
graduating  a  tube.     The  34.25  grains  of  mercury  are  to  be 
weighed  in,  the  tube  is  to  be  placed  against  the  wall,  slightly 
shaken  to  produce  a  level  surface,  and  then  a  division  is  to  be 
marked  by  the  file.     Another  34.25  grains  of  mercury  are  to 
be  weighed  into  the  tube  to  the  metal  already  contained  in  it, 
and  the  volume  is  to  be  marked  as  before;  third,  fourth,  and 
fifth  divisions  are  to  be  obtained  in  the  same  way,  and  thus  a 
scale  will  be  gradually  produced. 

138.  By  degrees  the  tube,  if  large,  will  contain  so  much 
mercury  as  to  be  too  heavy  for  the  balance.     But  it  is  then 
easy  to  use  a  smaller  vessel  to  weigh  the  metal  in,  transferring 
the  mercury  from  that  into  the  tube  each  time,  and  graduat- 
ing as  before.     One  advantage  of  thus  weighing  the  measur- 
ing portions  of  metal  in  a  separate  vessel  is,  that  water  may 
be  introduced  into  the  tube  under  graduation.     This  facili- 
tates the  production  of  the  level  surface  required  on  the  mer- 
cury, and  sometimes  assists  in  marking  down   the  gradua- 


84  GRADUATION  BY  MEASURE. 

tions  by  the  particular  appearance  of  the  tube:  but  as  dirty 
mercury  froths  more  readily  in  water  than  in  air,  the  opera- 
tor should  be  aware  of  any  error  in  bulk  that  might  arise  from 
this  cause:  and  a  little  time  should  also  be  allowed  before  a 
mark  is  made,  that  the  water  may  pass  to  the  surface  from 
between  the  glass  and  the  metal,  and  the  mercury  attain 
its  level.  No  quantity  of  water  that  is  worth  consideration 
will  remain  adhering  to  the  glass  after  it  has  stood  a  few  se- 
conds. 

139.  There  is  another  mode  of  obtaining  the  successive 
portions  of  mercury;  it  is  by  measuring  instead  of  weighing, 
yet  with  such  accuracy  as  to  be  unobjectionable,  and  is  as 
follows.  Procure  a  piece  of  glass  tube,  of  such  diameter  that 
the  division  required  shall  occupy  in  it  from  half  an  inch  to  an 
inch  in  length;  for  hundredths  it  may  be  one-sixth  of  an  inch 
internal  diameter,  and  for  tenths,  about  one-third  of  an  inch; 
draw  out  one  extremity  at  the  lamp  table,  so  as  to 
give  it  the  form  in  the  figure  (1181),  the  lower 
end  being  a  capillary  continuation,  from  which 
mercury  will  flow  out  in  a  small  stream,  by  the 
pressure  of  half  an  inch  of  metal  above.  Close 
the  lower  extremity  by  introducing  the  tip  into 
a  the  flame  of  a  spirit  lamp  so  that  the  sealed  part 
may  afterwards  be  cut  off  without  removing  more 
than  the  one-sixteenth  or  one-eighth  of  an  inch.  Counter- 
poise the  tube.  Now  weigh  into  it  (if  for  hundredths)  34.25 
grains  of  mercury,  or  if  for  tenths,  342.53  grains;  and  when 
the  weight  is  accurately  adjusted,  observe  whether  the  metal 
be  continuous  throughout;  if  not,  make  it  so.  The  only 
thing  which  will  interfere  with  this  continuity  is  the  occur- 
rence of  a  bubble  or  two  of  air  about  6  (see  the  figure). 
These  are  easily  removed  by  introducing  a  horse  hair  or  thin 
platinum  wire  down  between  the  glass  and  the  mercury,  until 
it  reaches  the  bubble,  the  air  of  which  will  immediately  pass 
up  by  the  hair  or  wire.  The  air  which  is  sure  to  remain  in 
the  capillary  part  may  be  removed  in  the  same  manner  as 
low  as  a,  but  it  is  better  that  a  small  but  constant  portion 


TUBE GRADUATION FACILITIES  OF  MEASUREMENT.         85 

should  remain  between  the  bottom  of  the  mercury  and  the 
sealed  part.  The  next  thing  to  be  done  is  to  mark  the  tube 
at  the  surface  of  the  mercury,  and  by  weighing  in  two,  three, 
four,  or  more  portions,  each  of  34.25  grains,  and  marking 
off  their  heights,  an  accurate  graduation  will  be  produced. 
Now  by  the  scratching  of  a  file,  and  then  a  little  lateral 
force  as  directed  in  glass-blowing  (1152),  cut  off  the  sealed 
capillary  end  about  halfway  below  a,  and  thus  open  that  ex- 
tremity. 

140.  The  measure  is  now  complete,  and  all  that  is  further 
requisite  is  the  mode  of  using  it.     Suppose  mercury,  equal  to 
one  or  more  divisions,  were  required  ;  pour  some  of  the  metal 
into  the  measure  above  its  highest  division,  at  the  same  time 
closing  its  capillary  opening  by  bearing  a  finger  slightly 
against  it ;  then  shutting  the  top  by  the  'fore  finger,  allow  the 
mercury  to  run  out  at  the  capillary  termination  (130),  until 
its  upper  surface  coincides  with  the  uppermost  line.     Now 
stop  the  stream  by  inclining  the  measure ;  until,  having  di- 
rected the  jet  into  the  tube  to  be  graduated,  any  mercury 
that  afterward  passes  out  may  be  received  by  it.     Again  re- 
lieve the  finger  above,  so  that  the  metal  may  fall  as  before, 
passing  through  the  extremity  into  the  lower  tube  ;  and  when 
the  level  in  the  measure  again  coincides  with  a  division,  it 
will  be  known  that  the  hundredth  of  a  cubic  inch  has  gone 
from  it  into  the  tube  to  be  graduated.     Prevent  the  passage 
of  more  mercury  by  inclining  the  measure ;  mark  off  the  por- 
tion already  transferred;  then  add  a  second  hundredth  in  the 
same  way,  and  proceed  in  this  manner  to  any  extent  required. 
When  once  a  measure  of  this  kind  is  made,  it  is  exceedingly 
convenient  and   ready  in  its  use,  and,  being  of  sufficient 
length,  will  readily  serve  to  estimate  tenths  as  well  as  hun- 
dredths. 

14  L  One  other  mode  of  measuring  the  mercury  in  these 
cases  of  graduation  it  will  be  necessary  to  mention,  because 
it  is  common,  and  at  times  has  peculiar  advantages.  It  con- 
sists in  forming  a  tube  which,  when  closed  with  the  finger, 
shall  hold  exactly  the  quantity  of  mercury  required.  The 
use  of  such  a  tube  requires  a  little  practice,  for  when  the  di- 
ameter is  more  than  the  third  of  an  inch,  variations  in  the 


86  MEASURES  FOR  TUBE  GRADUATION. 

pressure  of  the  finger  upon  its  open  end,  or  the  use  of  the 
finger  or  thumb  indifferently,  cause  sensible  variations  in  the 
quantity  contained.  By  practice  such  uniformity  is  obtained, 
however,  as  not  to  involve  any  important  error. 

142.  These  measures  are  best  made  in  the  following  man- 
ner :  select  a  piece  of  tube  sealed  at  one  end,  with  a  rounded 
termination,  and  which  shall   be  competent  to  hold  about 
twice  the  bulk  desired;  counterpoise  it,  and  then  weigh  in 
the  mercury  corresponding  to  the  volume  required.     Mark 
this  volume,  and,  pouring  the  mercury  into  another  tube  or 
dish,  cut  off  the  measure  (1152)  as  near  as  may  be  to  the 
mark;  leaving  it,  if  not  exact,  rather  larger  than  is  required. 
Draw  out  a  few  thick  threads  of  cement  (1123,  1125),  or 
make  a  thin  roll  of  wax,  and,  having  poured  the  mercury 
back  into  the  intended  measure,  put  upon  it  a  piece  or  two  of 
the  cement  or  wax,  and,  covering  it  with  the  ringer,  depress 
it  into  the  fluid  metal,  and  observe  whether  there  be  sufficient 
to  fill  the  tube  or  not;  the  wax  or  cement  is  to  be  increased 
or  diminished  in  bulk,  until  with  the  mercury  it  exactly  fills 
the  tube  when  closed  by  the  finger :  and  this  adjustment  is 
to  be  made  over  a  Wedgewood's  basin,  that  any  particles  of 
mercury  thrown  out  during  the  trial  may  be  readily  returned 
to  the  tube,  and  prevent  alteration  of  the  original  quantity. 
When  this  adjustment  of  the  wax  has  been  obtained,  pour 
out  the  mercury,  drop  the  wax  to  the  bottom  of  the  tube, 
warm  the  latter  so  as  to  melt  the  wax,  and  then  allowing  it 
to  cool,  the  measure  is  completed ;  but  for  greater  security, 
verify  it  by  ascertaining  that  it  does  measure  out  the  right 
weight  of  mercury. 

143.  It  is  not  necessary  in  every  case  to  weigh  out  mer- 
cury for  each  division  on  the  graduation  ;  for  when  the  divi- 
sions are  small,  as  on  a  comparatively  large  tube,  it  can 
frequently  be  effected  as  accurately,  or  more  so  by  the  unas- 
sisted eye,  as  by  measurement  with  mercury.     Thus5  for  in- 
stance, if  a  tube  of  one-fourth  of  an  inch  in  diameter  were  to 
be  graduated  into  tenths  and  hundredths  of  a  cubical  inch, 
and  by  measuring  every  four  hundredths  by  some  of  the  pre- 
ceding methods,  the  resulting  divisions  were  found  to  be  as 
nearly  as  possible  equal  in  length,  and  consequently  the  tube 


TUBE  GRADUATION TEST  OF  ACCURACY.          87 

uniform;  then  the  single  hundredths  may,  by  very  little  prac- 
tice, be  marked  off  by  the  eye  alone  more  accurately  than  by 
any  other  method  usually  adopted  in  the  laboratory,  and 
sufficiently  so  for  the  most  refined  experiments.  The  object 
is  of  course  to  divide  the  space  of  four  hundredths,  first  into 
two  of  two  hundredths,  and  each  of  these  into  two  of  one 
hundredth.  This  is  best  done,  not  by  holding  the  tube  verti- 
cally against  the  wall,  but  laying  it  horizontally  upon  the 
table  on  a  surface  of  uniform  colour  ;  and  the  division  should 
first  be  made  by  dots  as  before  mentioned  (132),  and  their 
uniform  and  accurate  distance  acknowledged  by  the  eye  be- 
fore the  lines  which  are  to  form  the  scale  are  marked.  Very 
little  experience  will  show  the  value  and  rapidity  of  this 
method,  which,  in  the  hands  of  a  eareful  person,  may  be  ex- 
tended to  the  division  of  a  space  into  5,  6,  8,  10,  or  even 
more  parts. 

144.  Where  the  mercury  is  measured  into  the  tube  to  be 
graduated,  every  five  or  ten  portions  put  in  should  be  trans- 
ferred to  the  balance  and  weighed,  to  ascertain  their  correct 
accordance  with  the  quantity  marked  on   the  graduation. 
Thus  supposing  the  measuring  tube  before  described  (139) 
to   be  in  use,  when  twenty  divisions  have  been   transferred 
from  it,  the  operator  should  ascertain  that  the  mercury  in  the 
tube  to  be  graduated  actually  amounts  to  twenty  times  34.25 
grains,  and  when  forty  divisions  have  been  put  in,  that  1370 
grains  of  mercury  are  there. 

All  these  experiments  relative  to  the  weighing  and  mea- 
suring of  mercury  should  be  made  on  a  tray,,  or  over  the 
mercury  table  (12). 

145.  In  marking  the  divisions,  every  fifth  and  tenth  should 
be  distinguished  from  the  others,  for  the    purpose  of  ready 
observation  ;  the  fifths  by  a  litlle  extra  length,  and  the  tenths 
by  being  marked  on  both  sides  of  the  upright  line,  as  indica- 
ting larger  divisions. 

146.  In  eudiometrical   and  other  experiments  with  small 
quantities  of  gas,  very  small  divisions  are  required,  and  some- 
times other  parts  than  those  of  the  tenths  or  hundredths  of  a 
cubical  inch  are,  from  their  size,  useful.     In  these  cases  it  is 
far  better  to  take  other  subdivisions  of  the  cubical  inch  than 


88  GRADUATION  OF  JARS. 

to  have  an  independent  standard,  and  through  it  introduce 
complexity  into  the  laboratory  measures.  If  hundredths  are 
not  small  enough,  divide  them  into  two  hundredths,  or  five 
hundredths,  or  thousandths  ;  or  if  hundredths  are  too  small, 
count  two  of  them  as  one  part,  which  may  easily  be  done  upon 
the  tubes  graduated  as  already  described ;  and  indeed  every 
other  division  may  be  distinguished  by  a  little  additional  mark 
opposite  to  it  on  the  other  side  of  the  perpendicular  line. 

147.  In  graduating-  tubes  for  eudiometry  or  any  other  pur- 
pose, Dr  Henry  has  long  been  in  the  habit  of  using  a  con- 
trivance which  renders  the  operation  greatly  quicker,  and 
insures  perfect  accuracy.     It  consists  of  a  tube  open  at  both 
ends,  and  not  more  than  0.08  of  an  inch  in  diameter.     This 
is  carefully  divided  into  equal  parts,  which  may  be  entirely 
arbitrary,  but  those  which  he  employed  are  ten  grains  of  mer- 
cury, at  60°  Fahrenheit,  the  whole  tube  containing  100  grains. 
It  is  some  trouble  to  divide  this  tube,  but  when  once  prepar- 
ed any  number  may  by  its  means  be  easily  graduated.     The 
successive  portions  of  mercury  used  in  dividing  wider  tubes 
are  measured  by  this,  into  which  they  are  drawn,  either  by 
plunging  it  into  a  jar  filled  to  sufficient  height  with  that  fluid, 
or  by  the  action  of  the  mouth*. 

148.  The  graduation  of  jars  is  to  be  effected  in  a  manner 
very  similar  to  that  which  has  been  recommended  for  tubes  ; 
but  if  performed  by  weighing,  water  is  a  better  substance  than 
mercury  for  all  quantities  above  half  a  cubic  inch,  because  of 
the  weight  of  the  latter,  and  the  consequent  burden  it  occa- 
sions to  the  balance.     A  cubic  inch  of  water  at  62°,  it  will 
be  remembered,  weighs  252.458  grains.     If  measures  are  to 
be  used,  the  vessels  for  them  should  be  perfectly  clean,  so  as 
to  become  wetted  over  the  interior :  they  should  be  well 
rinsed  out  with  water,  and  after  being  left  to  drain  for  a  few 
seconds,  should,  without  further  drying,  be  counterbalanced 
before  the  given  weight  of  water,  which  is  to  form  the  stan- 
dard, is  introduced,  and  its  volume  marked  (139,  141);  be- 
cause on  every  occasion  for  their  use  a  similar  quantity  of 

*  Manchester  Memoirs,  Second  Series,  vol.  it. 


GRADUATING  JARS.  89 

moisture  will  be  left  in  them,  after  the  liquid  by  which  the 
graduations  are  to  be  made  has  been  poured  into  the  jar. 

149.  In  marking  the  jars  it  will  not  be  advisable  to  place 
them  against  the  wall,  as  has  been  directed  for  tubes,  their 
larger  diameter  interfering  with  such  an  arrangement.    They 
should  be  put  upon  a  steady,  firm  place,  as  the  one  appoint- 
ed  for  measuring  (120) ;  and  the  liquid  having  acquired  a 
state  of  rest,  three  points  should  be  marked,  upon  upright 
and    equidistant   lines,  corresponding  accurately   with  the 
general  surface  of  the  water  in   the  jar.     These  points  are 
best  obtained  in  the  first  place  by  the  scratching-diamond 
(128,  974),  and  may  afterwards  be  extended  into  short  lines 
by  the  file  (132). 

150.  When  the  jars  to  be  graduated  are  such  as  cannot 
stand  steadily  upon  their  own  bases,  the  graduation  at  three 
different  places  becomes  still  more  important.     Thus  with 
such  as  are  capped,  and,  being  closed  with  a  stop-cock,  re- 
quire, when  graduated,  to  be  supported  on  other  jars,  or  list 
rings  (68),  or  over  holes,  the  triple  graduation  is  a  security 
independent  of  a  correct  perpendicular  position.     For  though 
the  jar  might  perchance  shift  a  little  in  its  situation  from  the 
perpendicular,  still  if  any  quantity  of  water,  for  instance  20 
cubic  inches,  were  then  marked  off  by  three  lines  on  different 
sides   of  the   glass,   any  quantity   which  at  a  future  time 
should  coincide  with  those  marks,  would  be  known  to  be  ac- 
curately 20  cubic  inches.     This  might  be  effected,  indeed, 
by  two  graduations  on  opposite  sides,  but  it  would  not  be  so 
certain  in  practice  as  three.     In  using  three,  also,  the  two 
first,  if  minutely  incorrect,  may  be  adjusted  to  perfect  accu- 
racy, by  very  slight  motion  of  the  jar  before  the  third  mark 
is  made.     The  necessity  of  making  these  graduations  at  one 
temperature,  that  of  62°,  has  been  before  insisted  upon. 

151.  Several  instruments  have  been  constructed  by  Dr 
Hare*,  in  which  he  has  introduced  a  mode  of  measuring,  de- 
pendent upon  the  displacement  of  certain  volumes  of  liquids 
or  gases,  by  the  different  parts  of  a  graduated  rod.     The 

*  Phil.  Mag.  Ixvii.  21.    Hare's  minutes,  pp.  124,  125, 

M 


90  HARE'S  SLIDING  HOD — MEASURER, 

figure  represents  one  of  these  in- 
struments. It  consists  of  a  glass 
tube  fixed  by  one  extremity  into  a 
cap  and  collar  of  leather,  and  ter- 
minated at  the  other  in  a  capillary 
opening.  A  rod  graduated  into  equal  parts  passes  air-tight 
through  the  collar  of  leather,  and  is  moved  by  a  handle  at 
the  exterior.  If  the  aperture  be  immersed  in  water,  and  the 
rod  drawn  out  and  thrust  in  again  several  times,  the  air  is 
ejected,  water  enters,  and  by  inclining  the  instrument  it  may 
be  entirely  filled  with  the  latter  -fluid,  and  left  with  the 
greater  part  of  the  rod  in  the  air.  If  it  be  then  removed 
from  the  water  and  dried,  it  is  evident  that,  by  inserting  the 
rod,  an  equal  volume  of  the  water  will  be  expelled  from  the 
tube  by  the  capillary  aperture,  and  may  be  transferred  into 
the  vessels  to  be  graduated  ;  it  is  also  evident  that  this  water 
may  be  thrown  out  in  successive  minute  portions,  each  equal 
to  the  others  and  to  one  of  the  graduations  on  the  rod. 
When  the  whole  of  the  rod  is  thrust  in,  it  is  easy,  by  draw- 
ing it  out,  to  replace  it  by  water,  as  in  the  filling  of  the  in- 
strument, and  then  additional  equal  bulks  of  water  may  be 
measured  out. 

152.  By  terminating  the  tube  as  before  described  (130), 
and  using  mercury  instead  of  water,  the  instrument  becomes 
an  excellent  measurer  of  equal  portions  of  mercury,  and  may 
then  be  used  in  graduating  tubes  (137).     The  rod  itself  is 
easily  graduated  to  any  required  dimensions,  by  observing 
how  much  of  its  length  must  be  inserted  to  displace  a  given 
weight  of  mercury,  as  34.25  grains  (137),  and  then  by  pro- 
ceeding to  mark  off  other  degrees  of  equal  value*. 

153.  An  instrument  of  this  kind  may  be  made  without 
difficulty,   from  a  tube  like  that  figured  at  p.  71  ;  the  rod 
may  be  of  solid  glass,  or  a  glass  tube  closed  at  the  inner  ter- 
mination; it  should  be  made  to  slide  through  some  tow,  well 
impregnated  with  tallow,  which,  being  wrapped  around  it,  is 
to  form  a  plug  sufficient  to  close  the  end  of  the  tube.     By 
tying  this  over  with  a  piece  of  cloth,  it  may  be  made  quite 
firm  and  air-tight ;  and  the  rod  may  then  be  graduated  ex- 
perimentally. 

*  Seep. 


SOURCES  AND  MANAGEMENT  OF  HEAT.  91 

154.  The  following  are  useful  estimates  and  comparisons 
of  certain  measures,  both  linear  and  cubic,  with  the  weights 
of  the  cubic  measures  in  grains  of  distilled  water  added: 

Inches. 

Yard        36 

Metre 39.37079 

Decimetre  .....  3.93708 
Centimetre  .....  0.39370 
Millimetre 0.03937 

The  seconds  pendulum  vibrating  at  London,  39,13929. 

Cubic  Inches.  Grains  of  distilled  Water, 

Imperial  gallon   .     .    277.274  70000 

Imperial  pint  .     .     .      34.65925       a?50 

Imperial  fluid  ounce          1.7329625 437.5 

The  old  wine  pint  28.8827        7291.666 

Cubic  Inches.  Grains  of  distilled  water. 

Old  fluid  ounce  .     .    1.805169        455.73 

Cubic  inch      ...     1.                ' 252.458 

Litre     .....  61.02525          15406.312 

Decilitre    ....    6.10252          1540.631 

Centilitre  ....    0.61025          154.063 

Millilitre    .               .    0.06102  15.406 


SECTION  IV. 
SOURCES  AND  MANAGEMENT  OF  HEAT. 

155.  HEAT  is  so  important,  as  modifying  chemical  action, 
and  the  chemical  and  physical  properties  of  bodies,  that  it 
must  always  be  of  the  utmost  consequence  to  the  chemist. 
So  great  is  its  influence  over  his  researches,  that  he  has  been 
called  the  philosopher  by  fire;  and  though  the  consideration 
of  its  peculiar  action  on  matter  forms  no  part  of  the  direct 
subject  of  the  present  volume,  yet,  as  the  modes  of  augment- 
ing and  applying  it  are  proportionate  in  number  and  extent 
to  the  powers  of  the  agent  itself,  so  the  sources  and  manage- 


92  FURNACES. 

ment  of  heat  will  claim  much  present  attention.  It  is,  how- 
ever, by  no  means  intended  here  to  dwell  upon  this  subject 
in  its  full  extent,  but  rather  to  limit  and  compress  it  as  much 
as  possible;  supplying  to  the  student  that  portion  of  instruc- 
tion which  relates  to  the  simplest  and  most  effectual  means 
of  obtaining  the  temperatures  he  may  require  in  his  experi- 
ments, but  not  extending  it  to  every  furnace,  lamp,  or  blow- 
pipe, or  even  to  every  one  beneficially  used  in  chemical  arts 
and  processes. 

§  1.  Furnaces. 

156.  There  is  scarcely  any  limit  to  the  number  of  furnaces 
that  have  been  contrived  as  particularly  adapted  either  for 
special  or  general  uses;  all  no  doubt  were  good  at  the  time 
they  were  devised,  and  superior  for  some  reason  or  other  to 
those  which  had  preceded  them.     But  the  character  of  che- 
mical operations  has  changed  so  much  as  to  render  many  of 
these  contrivances  useless,  or  of  little  importance,  and  each 
person  is  now  left  to  select  those  which  are  most  agreeable 
to  himself,  as  according  best  with  either  his  notions  or  modes 
of  experimenting.     For  these  reasons  the  author  will  here 
describe  those  which  he  has  been  induced  to  adopt  as  eco- 
nomical and  effectual ;  convinced  that  he  ought  not  to  omit 
them,  and  that  to  describe  a  greater  number  would  be  as- 
signing to  this  subject  a  larger  proportion  of  the  present  vo- 
lume than  it  can  fairly  claim. 

157.  An  exceedingly  useful  furnace,  either  in  a  large  or 
small  laboratory,  may  be  made  out  of  a  black  lead  or  earthen 
crucible.     The  proper  vessels  for  this  purpose  are  known  by 
the  name  of  blue  pots,  and  may  be  had  of  almost  every  size, 
less  than  the  height  of  22  inches,  and  of  12  or  14  inches  dia- 
meter at  the  top;  they  are  made  of  clay  and  plumbago  mixed, 
and  are  easily  cut  by  a  saw,  rasp,  or  file. 

158.  One  of  these  vessels,  of  the  height  of  12  inches,  and 
7  inches  in  width  at  the  top  within,  will  make  a  very  useful 
furnace  for  the  igniting  a  small  crucible,  healing  a  tube,  or 
distilling  with  large  glass  retorts  at  moderate  temperatures, 
or  with  smaller  glass  or  earthen  retorts  at  higher  temperatures. 
It  is  in  the  course  of  preparation  necessary  first  to  have  cer- 


CRUCIBLE  FURNACE BINDING GRATE.  93 

tain  round  holes  pierced  in  it.  These  are  easily  made;  a 
gimlet,  brad-awl,  or  other  small  instrument,  is  to  be  used,  to 
penetrate  the  sides,  and  the  small  apertures  thus 
produced  are  to  be  enlarged  with  a  rat's-tail 
and  round  rasp,  and  ultimately  finished  with  a 
half-round  rasp,  which  will  make  them  of  the 
size  required.  Four  of  these  holes  are  to  be 
placed  at  equal  distances  from  each  other,  and 
about  two  inches  from  the  bottom  of  the  pot ; 
they  may  be  1*  or  li  inches  in  diameter;  a  second  ring  of 
holes,  five  or  six  in  number,  is  to  be  made  half  way  between 
the  top  and  bottom  of  the  pot,  and  a  third  row  of  five  or  six 
within  two  inches  of  the  top  ;  these  holes  should  be  rather 
smaller  than  the  four  lower  ones. 

159.  The  pot  should  now  be  bound  round  with  iron  or 
copper  wire,  T^  of  an  inch  thick,  to  strengthen  and  hold  it 
together  when  it  cracks, — an  effect  which  is  sure  to  take 
place  after  it  has  been  a  few  times  heated.  The  wire  should 
be  carried  round  in  three  different  places,  just  above  the 
upper  holes  between  the  top  and  second  row,  and  between 
the  second  and  lowermost  row.  A  single  wire,  especially 
if  of  iron,  is  sufficient,  and  two  or  three  long  notches  should 
be  made  with  the  edge  of  a  rasp  in  the  line  of  each  ring  of 
wire,  just  deep  enough  to  receive  it  and  prevent  it  from  slip- 
ping down  when  drawn  tight ;  and  the  ends  should  then  be 
twisted  together.  It  is  very  convenient  to  have  a  handle  to 
these  furnaces,  by  which  they  may  be  lifted,  when  hot,  with 
a  pair  of  tongs  or  a  hook.  It  should  be  of  iron  wire  one- 
eighth  or  more  of  an  inch  in  thickness;  one  piece  should 
be  carried  under  the  pot,  and  lodged  in  a  groove  deep 
enough  to  receive  it,  and  prevent  unsteadiness;  it  should 
rise  up  on  opposite  sides  of  the  furnace,  until  near  the  top, 
and  there  be  turned  so  as  to  form  a  hook  or  ring  on  each 
side  to  receive  the  handle.  This  wire  should  be  put  on  at 
the  same  time  with  that  which  binds  the  whole  together, 
and  the  latter  wires  should  take  a  turn  round  the  former 
wherever  they  cross  it,  which  will  add  considerably  to  the 
strength  of  the  whole.  The  handle  above  is  easily  made  of 
a  piece  of  the  same  thick  wire  curved  over  the  top  of  the 


94  FURNACE    GRATE FUEL. 

furnace,  and  bent  into  hooks  at  the  extremities,  by  which  it  is 
to  be  attached  to  the  former  piece.  The  handle  should  have 
such  a  curve  that  when  not  in  use  it  may  pass  over  the  edge 
and  lie  out  of  the  way  against  the  side  of  the  furnace. 

160.  A  small  round  movable  grate  of  cast  iron,  like  that 

figured  in  the  woodcut,  makes  this  furnace  com- 
plete for  many  operations.  If  it  be  required  to 
heat  a  crucible,  the  grate  should  be  of  such  a 
size  as  to  drop  into  the  furnace,  and  rest  between 
the  bottom  and  the  second  row  of  holes.  The 
part  below  then  forms  the  ash-pit,  to  be  supplied  with  air 
for  the  fire  by  the  four  holes  ;  and  the  part  above  forms  the 
body  of  the  furnace  to  receive  the  fire  and  crucible.  If  a 
shallow  fire  only  is  wanted,  as  in  process  of  distillation  or 
the  heating  of  tubes,  the  grate  should  be  of  such  a  size  as, 
when  dropped  into  the  furnace,  to  descend  only  a  little  be- 
low the  first  tier  of  holes,  the  ash-pit  then  having  two  tier 
of  holes  entering  it.  Haifa  dozen  of  these  small  grates  will 
be  required  in  the  laboratory,  for  the  purpose  of  fitting  at 
different  times  into  different  parts  of  the  same  furnace,  and 
also  for  use  in  different-sized  furnaces,  of  the  kind  now  de- 
scribed. They  are  of  small  price,  and  may  be  bought  of 
the  philosophical  instrument-maker. 

161.  When  furnaces  of  this  sort  are  constructed  of  diffe- 
rent sizes,  variations  in  the  number  and  arrangement  of  the 
air-holes  will  of  course  suggest  themselves.     A  smaller  fur- 
nace will  require  only  two  tiers  of  holes ;  one  of  three  or 
four  for  the  ashpit,  and  another  for  the  body  of  the  furnace. 
A  larger  furnace  may  require  more  holes,  and  may  at  times 
have  those  which  communicate  with  the  ash-pit  enlarged 
into  other  forms,  and  furnished  with  stoppers  of  soft  red 
brick  (1354),  or  pieces  of  old  pots. 

162.  The  fuel  used  with  these  furnaces  is  charcoal,  or  in 
the  larger  ones  charcoal  mixed  with  coke. 

163.  The  fire  is  considerably  under  command,  both  as  to 
the   diminution  and  increase  of  its  intensity.     A  box  of 
round  stoppers,  made  of  soft  brick  (1354),  or  old  blue  pots, 
and  something  like  corks   in   form,  should   be   provided. 
These  serve  to  close  the  air-holes  which  lead  either  to  the 


ADDITIONS TEMPORARY    FLUE.  95 

ash-pit  or  directly  to  the  fire,  and  by  limiting  the  quantity 
of  air  which  enters,  reduce  the  combustion  in  any  required 
degree.  When  the  grate  is  placed  high  up  in  the  furnace, 
as  for  distillations,  these  stoppers  are  frequently  required  for 
the  lower  holes. 

164.  On  the  contrary,  to  increase  temperature,  and  some- 
times to  increase  the  body  of  fuel,  additions  are  made  at  the 

top  of  the  furnace.  A  very  useful  one  consists 
of  the  upper  part  of  an  old  crucible,  cut  off 
so  as  to  form  a  ring,  which  should  be  bound 
with  wire  as  was  directed  in  regard  to  the 
furnace  (159).  Rings  of  this  kind  may  be 
rom  an  inch  to  three  inches  or  more  in  depth ;  and  when 
placed  upon  the  top  of  the  furnace,  so  as  to  form  a  continu- 
ation of  it  in  height,  they  considerably  increase  both  the 
capacity  and  the  draught.  They  may  be  made  with  holes 
or  not,  according  to  their  depth.  Such  holes  of  course 
weaken  the  ring,  but  when  the  quantity  of  fuel  in  the  fire 
is  increased,  it  is  frequently  necessary  to  increase  the  supply 
of  air  also ;  and  when  a  crucible  stands  in  the  middle  of  the 
mass  of  fuel,  these  lateral  supplies  of  air,  especially  in  the 
smaller  furnaces,  are  essential  to  the  vividness  of  combus- 
tion, and  the  high  temperature  required. 

165.  A  most  useful  accompaniment  to  these  small  porta- 

ble furnaces  is  a  piece  of  straight  funnel- 
pipe,  about  two  feet  long,  four  inches  in 
width,  and  opening  out  below  funnel  fash- 
ion, until  it  is  about  eight  inches  in  diame- 
ter. This  will  easily  rest  upon  any  furnace 
not  more  than  eight  inches,  nor  less  than 
four  or  five  inches  wide ;  is  quickly  put  on 
or  off;  stands  steadily  of  itself,  and  in- 
creases the  draught  powerfully.  A  wooden 
handle  may  be  attached  to  it  for  conveni- 
ence ;  or  without  it  the  tongs  will  serve  to 
remove  it.  It  may  either  be  taken  off  when  the  fire  requires 
to  be  made  up,  or  the  pieces  of  charcoal  may  be  dropped 
in  from  above.  There  is  no  difficulty  in  raising  a  crucible 


96       CRUCIBLE  FURNACE ATTACHED  TO  FLUES. 

two  inches  and  a  half  in  diameter  to  a  white  heat,  by  a  fur- 
nace of  this  kind,  and  of  the  dimensions  before  stated  (158); 
and  that  in  any  situation  which  may  be  convenient  upon  the 
tables  or  the  floor,  and  with  all  the  advantage  of  arranging 
or  dismounting  the  apparatus  with  extreme  facility.  The 
ignitings  and  heatings  which  belong  to  the  analysis  of 
siliceous  and  other  minerals,  have  long  been  made  in  fur- 
naces of  this  kind  at  the  Royal  Institution. 

166.  To  fit  this  furnace  for  the  igniting  of  tubes,  it  is 
useful  to  cut  a  couple  of  notches  in  its  upper  edge,  about 
an  inch  deep,  in  which  the  tube  may  be  laid  when  the  grate 
is  high  in  the  furnace  ;  at  other  times  when  a  smaller  heated 
length  only  is  wanted,  it  may  be  passed  through  two  opposite 
holes  lower  down  in  the  furnace.     When  heating  a  tube  in 
this  manner,  it  is  not  necessary  to  have  a  greater  space  than 
an  inch  or  an  inch  and  a  half  between  it  and  the  grate. 

167.  When  these  furnaces  are  made  out  of  large  pots, 
the  grates  being  upwards  of  six  inches  in  diameter,  and  the 
fuel  chamber  six  or  eight  inches,  high,  they  become  very 
powerful,  and  may  be  used  to  heat  crucibles  of  considerable 
size.     From  the  larger  dimensions  of  the  grate,  it  is  gene- 
rally unnecessary  to  form  lateral  air-holes  through  the  body 
of  the  furnace,  but  it  is  then  requisite  that  an  abundant  sup- 
ply of  air  be  admitted  to  the  ash-pit,  and  through  the  grate 
to  the  fire.     The  fuel  used  in  these  larger  furnaces  should 
be  a  mixture  of  coke  and  charcoal,  or  sometimes,  when  a 
durable  fire  is  required  for  long  operations,  coke  alone  ;  for 
in  such  cases  the  rapidity  with  which  charcoal  burns  away 
is  inconvenient,  and  the  heat  which  it  produces  may  be  at- 
tained with  coke  by  improving  the  draught*. 

168.  These  furnaces  may,  when  the  employment  of  the 

*  In  this  city  coke  cannot  be  obtained;  but  for  durable  fires  the  purest  an- 
thracite answers  every  purpose. — ED. 


TABLE-FURNACE. 


97 


highest  heat  is  desirable,  be  advantage- 
ously connected  with  the  spare  laboratory 
flue  (5),  and  the  openings  of  that  flue 
should  be  above  the  level  of  the  furnaces 
when  they  stand  on  the  floor.  The  com- 
munication is  easily  effected  by  two  or 
three  short  pieces  of  funnel-pipe  like  those 
in  the  margin,  made  to  fit  into  each  other; 
one  having  a  funnel  termination  at  the 
bottom,  lined  with  fire-clay,  to  adapt  it  to 
the  furnace,  and  another  a  bend  or  joint 
at  right  angles.  The  pipe  should  be  at 
least  four  inches  in  diameter.  These  fur- 
naces, thus  arranged,  are  very  powerful, 
and,  being  sometimes  wanted  for  long  op- 
erations, require-to  be  fed  without  disturb- 
ance of  the  arrangement ;  for  which  reason 
it  is  proper  to  have  an  aperture  in  the  fun- 
nel-pipe, by  which  fuel  can  be  introduced, 
and  which  may  be  closed  by  a  stopper, 
when  the  fire  is  in  order.  Another,  and, 
at  times,  a  more  convenient  mode  of  arrangement,  is  to  con- 
tinue the  furnace  upwards  by  a  deep  ring  (being  the  upper 
part  of  another  pot)  in  which  is  an  aperture  by  which  the 
fire  can  be  fed  when  required,  but  which  can  be  closed  by  a 
stopper  when  not  in  use.  .The  funnel-pipe  is  then  to  extend 
from  the  top  of  this  ring  to  the  hole  of  the  flue  in  the  wall. 
These  large  furnaces  should  be  bound  with  iron  hoop. 

For  further  information  relative  to  these  kinds  of  furna- 
ces, see  Lewis's  Philosophical  Commerce  of  the  Arts,  pp. 
1—37. 

169.  The  furnace  next  requiring  description  is  that  in- 
tended for  general  laboratory  use,  and  already  referred  to 
(8).  Being  in  constant  requisition  as  a  table,  it  should  be 
about  34  or  35  inches  in  height;  its  other  dimensions,  and 
even  its  form,  must  depend  upon  the  space  that  can  be  al- 
N 


93 


TABLE-FURNACE ITS  SIZE. 


lotted  for  it.  The  one  in  the  laboratory  of  the  Royal  Insti- 
tution, constructed  several  years  since,  under  the  direction 
of  Mr  JBrande,  has  the  brick-work  52  inches  in  length,  and 
30  inches  in  width;  the  iron  plate,  including  sand-baths,  be- 
ing 57  inches  by  42;  others  have  been  constructed,  the 
plates  of  which  are  only  40  inches  by  27.  The  principal 
part  of  this  furnace  is  necessarily  of  brick-work,  only  the 

top  plate,  with  the  baths  and 
the  front,  being  of  iron.  The 
front  is  a  curved  plate,  having 
two  apertures  closed  by  iron 
doors;  one  belonging  to  the  fire- 
place, and  the  other  to  the  ash- 
pit. It  is  34  inches  high,  and 
14  inches  wide.  The  ash-hole 
door  moves  over  the  flooring  beneath;  the  bottom  of  the 
fire-place  door  is  22  inches  from  the  ground,  and  the  door 
itself  is  8i  inches  by  7.  This  front  is  guarded  within  at 
the  part  which  incloses  the  fire  by  a  strong  cast-iron  plate, 
having  an  opening  through  it  corresponding  to  the  door 
of  the  fire-place.  It  has  clamps  attached  to  it,  which,  when 
the  furnace  is  built  up,  are  inclosed  in  the  brick-work. 

170.  In  the  setting  or  building  of  the  furnace,  two  lateral 
brick  walls  are  raised  on  each  side  of  the  front  plate,  and  a 
back-wall  at  such  a  distance  from  it  as  to  leave  space  for 
the  ash-hole  and  fire-place ;  these  walls  are  lined  with  Welsh 
lumps,  where  they  form  the  fire-chamber:  two  iron  bars  are 
inserted  in  the  course  of  the  work  to  support  the  loose  grate 
bars  in  the  usual  manner,  the  grate  being  raised  19  inches 
from  the  ground.  The  side-walls  are  continued  until  of  the 
height  of  the  front,  and  are  carried  backward  from  the  front 
in  two  parallel  lines,  so  as  to  afford  support  for  the  iron 
plate  which  is  to  cover  the  whole.  The  back-wall  of  the 
fire-place  is  not  raised  so  high  as  the  side-walls  by  six  inches 
and  a  half,  the  interval  which  is  left  between  it  and  the  bot- 
tom of  the  sand-bath  being  the  commencement  of  the  flue 
or  throat  of  the  furnace.  In  this  way  the  fire-place,  which 
is  fourteen  inches  from  back  to  front,  and  nine  inches 


TABLE-FURNACE PARTS.  99 

is  formed,  and  also  the  two  sides  of  the  portion  of  horizontal 
flue  which  belongs  to  the  furnace,  and  is  intended  to  heat 
the  larger  sand-bath.  The  bottom  of  this  part  of  the  flue 
may  be  made  of  brick-work,  resting  upon  bearers  laid  on 
the  two  side-walls,  or  it  may  be  a  plate  of  cast-iron  resting 
upon  a  ledge  of  the  brick-work  on  each  side,  and  on  the  top 
of  the  wall,  which  forms  the  back  of  the  fire-place.  When 
such  an  arrangement  is  adopted,  the  plate  must  not  be  built 
into  the  brick-work,  but  suffered  to  lie  on  the  ledges,  which 
are  to  be  made  flat  and  true  for  the  purpose ;  for,  if  attach- 
ed to  the  walls,  it  will,  by  alternate  expansion  and  contrac- 
tion, disturb  and  throw  them  down.  The  ends  of  the  side- 
walls,  forming  as  it  were  the  back  of  the  furnace,  may  be 
finished  either  by  being  carried  to  the  wall  against  which 
the  furtiace  is  built,  or  inclosed  by  a  piece  of  connecting 
brick-work,  to  make  the  whole  square  and  complete,  or  a 
warm  air  cupboard  may  be  formed  in  the  cavity  beneath  the 
flue,  and  the  door  made  to  occupy  the  opening  between  the 
walls.  Occasionally  the  flue  may  be  required  to  descend 
there,  and  pass  some  distance  under  ground.  These  points 
should  be  arranged  and  prepared  before  the  plate  constitut- 
ing the  top  of  the  furnace  is  put  on  to  the  brick-work,  so  that 
when  the  plate  with  its  sand-baths  is  in  its  place,  it  may 
complete  the  portion  of  horizontal  flue  by  forming  its  upper 
side. 

171.  The  size  of  this  plate  is  the  first  thing  to  be  considered, 
and  having  been  determined  upon,  from  a  consideration  of  the 
situation  to  be  occupied  by  the  furnace,  and  the  places  of  the 
sand-baths  having  also  been  arranged,  the  brick-work  must  then 
be  carried  up,  so  as  to  correspond  with  these  determinations, 
and  with  the  plate  itself,  which  in  the  mean  time  is  to  be  cast. 
The  sand-baths  and  the  plate  are  to  be  formed  in  separ- 
ate pieces.  The  bath  over  the  fire  is  best  of  a  circular 
form,  and  of  such  diameter  that,  when  lifted  out  of  its 
place,  it  may  leave  an  aperture  in  the  plate  equal  in  width 
to  the  upper  part  of  the  fire-place  beneath  ;  so  that  a  still, 
or  cast-iron  pot,  or  a  set  of  rings  may  be  put  irt^o  its  place 
over  the  fire.  The  other  sand-bath  must  be  of  siich  a  form 


100 


TABLE-FURNACE PLATE SAND-BATHS. 


p 


as  to  correspond  with  the  shape  and  size  of  the  flue  be- 
neath. These  vessels  are  to  be  of  cast-iron,  about  three- 
tenths  of  an  inch  thick;  their  depth  is  to  be  two  inches  and 
a  half  or  three  inches,  and  they  are  to  be  cast  with  flanches, 
so  as  to  rest  in  the  corresponding  depressions  of  the  plate,  that 

the  level  of  the  junctions  may 
be  uniform.  This  will  be  un- 
derstood from  the  accompany- 
ing section  of  the  furnace, 
given  through  the  line  AB  of 
the  view  (169).  It  is  essential 
that  these  sand-baths  be  of  such 

dimensions  as  to  fit  very  loosely  into  the  apertures  in  the 
plate,  when  cold,  a  space  of  the  eighth  of  an  inch  or  more 
being  left  all  round  them,  as  shown  in  the  section  ;  other- 
wise, when  heated,  they  will  expand  so  much  as  entirely  to 
fill  the  apertures,  and  even  break  the  plate.  The  plate 
itself  should  be  half  an  inch  thick. 

172.  When  the  plate  and   its  sand-baths  are  prepared, 
and  the  brick-work  is  ready,  the  furnace  is  finished  by  lay- 
ing the  plate  on  the  brick-work,  with  a  bed  of  mortar  inter- 
vening.    If  the  walls  are  thin,  or  any  peculiarity   in   their 
arrangement  occasions  weakness,  they  should  be  bound  to- 
gether within  by  cranks  built  into  the  work,  and  without  by 
iron  bands.     The   alternate   changes  of  temperature   from 
high  to  low,  and  low  to  high,  to  which  the  furnace  is  con- 
stantly subject,  render  it  liable  to  mechanical  injury,  in   a 
degree  much  surpassing  that  which  would  occur  to  a  similar 
piece  of  brick-work,  always  retained  nearly  at  one  tempera- 
ture.    The  square  space  inclosed  by  the  fire-place  and  flues 
may  be  converted   into   an   excellent  drying  or  warm  air 
chamber  if  desired  (606). 

173.  The    sand-baths   which    have    been   described    are 
liable  to  an   accident,  that  has   induced  some  chemists  to 
substitute  others  made  of  wrought  iron.     When  first  heated 
they  frequently,  indeed  generally,  crack  from  the  unequal 
expansion  in  different  parts;  and  the  plate  itself  is  subject 
to  the  same  accident.     If  constructed  of  wrought  iron,  this 


TABLE-FURNACE SAND-BATHS — RINGS.  • 

-   ,  , 

effect  is  not  produced ;  but  then  after  being  used  for  some 
time  they  warp  into  very  irregular  and  inconvenient  forms, 
especially  if  made  of  thin  metal;  whilst,  on  the  contrary, 
these  of  cast-iron,  when  cracked,  are  rarely  injured  for  the 
uses  to  which  they  are  to  be  applied,  and  seldom  suffer 
further  change. 

174.  These  baths  should  have  washed  river  or  sharp  sand 
put  into  them  (24) ;  it  is  heavy,  and  occasions  no  dust  when 
moved,  whilst,  on  the  contrary,   unwashed   and  bad  sand 
contains  much  dirt,  and  occasions  great  injury  in  experi- 
menting.    A  piece  of  straightened  iron  hoop,  about  twelve 
inches  in  length,  should  lie  on  the  furnace,  as  an  accom- 
paniment to  the  baths,  being  a  sort  of  coarse  spatula  with 
which  to  move  about  the  sand  (256 — 381). 

175.  These  baths  are  frequently  used  not  for  their  espe- 
cial objects,  but  for  the  purpose  of  supplying  heat  general- 
ly to  the  laboratory;  for  the  sand  being  cleared  off  the  bot- 
tom of  the  bath  towards  one  end,  leaves  the  metal  uncover- 
ed, which  then  rapidly  communicates  heat  to  the  air,  and 
acts  with  the  full  and  economical  effect  of  a  stove.     The 
same  arrangement  produces  a  current  of  hot  air  upwards, 
which  may  frequently  be  used  to  warm  apparatus,  to  heat 
plates  for  drying  filters,  &c. 

176.  The  circular  sand-bath  is  frequently  replaced  by  a 
set  of  concentric  iron  rings,  or  a  cast-iron  pot.     The  rings 

are  convenient  for  leaving  an  aperture 
over  the  fire  of  larger  or  smaller  di- 
mensions, according  as  a  smaller  or 
larger  number  are  used  at  once ;  and 
being  bevelled  at  the  edges,  fit  accu- 
rately into  each  other,  without  any  .risk 
of  becoming  fixed  by  expansion.  The 
external  one,  like  the  sand-baths  (171), 
should  be  m.ade  smaller  than  the  depression  in  the  furnace- 
plate  in  which  it  r,ests.  The  iron  pots  are  of  various  sizes, 
and  are  adapted  to  the  furnace  by  means  of  the  rings;  a 
red  heat  for  sublimation  is  easily  obtained  in  them. 

177.  Occasionally  the  sand-bath  is  replaced  by  a  still,  for- 


.*/«"«   , TONGS WIND-FURNACES. 

the  production  of  distilled  water  (26).  The  form  of  the  aper- 
ture and  furnace  is  such  as  to  enable  the  still  to  be  placed 
very  advantageously  as  relates  to  the  fire  beneath. 

178.  Tongs  are  essential  accompaniments  to  furnaces. 
There  are  many  forms  of  these  necessary  implements;  those 
which  have  the  rivet  in  the  middle  of  their  length,  so  as  to 
allow  of  considerable  opening  at  their  extremity,  and  also 
have  the  ends  bent  downward,  are  best  for  common  use.  They 

should  be  of  different  lengths,  from 
a  foot  to  two  feet ;  and  there 
should  be  one  or  two  pair  having 
the  rivet  near  the  extremity,  by 
which  a  powerful  hold  is  obtained,  so  as  to  prevent  the  slip- 
ping of  a  heavy  weight  from  between  them. 

179.  Mr.  Knight,  of  Foster-lane,  has  contrived  a  small 
furnace,  which,  at  the  same  time  that  it  is  competent  for  the 
performance  of  numerous  chemical  operations,  is  generally 
convenient  for  its  lightness  and  portability.     It  is  described 
with  several  others  in  many  chemical  works.     The  points  of 
manipulation  peculiar  to  each  become  evident  upon  inspec- 
tion. 

180.  Wind-furnaces  are  such  as  have  their  combustion 
urged  by  a  draught  of  air  through  them,  dependent  upon  the 
flue  to  which  they  are  attached.     They  are  usual  amongst 
refiners,  and  those  who  melt  metals  in  pots,  as  well  as  in  the 
laboratory ;  hence  their  improvement  and  perfection  are  of 
great   importance.      The  table  furnace  already  described 
(8 — 169),  and  the  crucible  furnaces,  when  connected  with 
the  laboratory  flues,  are  wind  furnaces ;  but  by  proportion- 
ing the  size  of  the  chimney  to  that  of  the  furnace,  others 
may  be  constructed,  much  surpassing  these  in  the  intensity 
of  heat  produced.     It  has  been  found  that  the  combustion  is 
most  vivid  when  carried  on  in  a  furnace  of  equal  diameter 
with  the  flue  placed  immediately  over  it,  the  latter  being  of 
a  height  equal  to  about  thirty  times  its  diameter,  and  free 
access  of  air  to  the  grate  being  permitted.     But  in  practice, 
many  variations  are  introduced,  which,  though  they  diminish 
the  intensity  of  heat,  still  enable  the  worker  of  metals  to  heat 
a  larger  mass  of  matter  up  to  the  point  he  requires,  with 


BLAST-FURNACE.  103 

a  diminished  consumption  of  fuel,  and  consequently  at  a 
smaller  expense. 

181.  In  the  laboratory  of  research,  the  wind-furnace  may 
generally  be  replaced  with  advantage  by  the  blast-furnace; 
the  operations  being  more  manageable  and  expeditious,  and 
the  heat  greater  and  the  consumption  of  fuel  smaller.     By  a 
little  contrivance,  one   of  the  crucible  furnaces  before  de- 
scribed (158)  is  easily  converted  into  a  blast-furnace,  and  a 
very  high  temperature  for  small  vessels  obtained.     This  is 
done  by  closing  the  holes  of  the  ash-pit  with  the  stoppers 
(161),  except  one,  and  applying  to  that  the  nozzle  of  a  pair 
of  double-hand  bellows,  from  which  a  blast  is  to  be  urged, 
and  the  furnace  aided  at  the  same  time  by  the  piece  of  up- 
right funnel-pipe  (165) ;  the  fuel  is  to  be  charcoal. 

182.  Mr.  Charles  Aiken  has  devised  an  arrangement  for 
a  blast-furnace  on  a  small  scale,  which  is  exceedingly  good 

and  powerful.  The  furnace 
is  made  out  of  fragments  of 
broken  blue  pots, and  consists 
of  several  parts,  sections  of 
which  are  here  given,  drawn 
upon  a  scale  of  one  inch  to 

•'^      jjj  Hlcnal^  ten.     The  lower  piece  a  is 

fitted  into  a  tin  bottom,  con- 
sisting of  a  circular  plate  with 
a  rising  rim ;  the  junction 
being  made  tight  by  plaster 
of  Paris.  The  piece  6,  resting  upon  a,  is  so  formed  as  to 
have  three  circular  shoulders  running  round  the  inside,  one 
at  g,  a  second  at  h,  and  a  third  a  little  lower,  namely,  where 
the  grate  in  section  is  observed  to  rest.  The  grate  is  circu- 
lar, and  can  be  removed  at  pleasure.  The  piece  c  is  merely 
a  broad  rim,  which,  resting  upon  the  edge  of  the  piece  6, 
increases  the  capacity  of  the  furnace.  The  piece  d  is  to  be 
used  when,  in  place  of  enlarging  the  fire,  it  is  required  to  be 
diminished.  It  is  to  be  placed  within  6,  resting  at  its  lower 
edge  on  the  rim  or  shoulder  h:  e  is  a  similar  piece,  but 
smaller,  it  rests  also  on  the  shoulder  h:  it  has  a  notch  half 
way  between  the  upper  and  the  lower  edge,  to  admit  the  stem 


104 

of  a  tobacco-pipe,  or  other  similarly-formed  article.  Another 
part  of  the  furnace  is  a  circular  plate  of  sheet  iron,  and  of 
such  a  diameter  as  to  fit  into  the  rim  g;  this  plate  is  perfo- 
rated with  an  aperture  three  inches  and  a  half  in  width,  into 
which  a  very  small  furnace-body  fits,  having  its  lower  part 
pierced  with  holes  instead  of  a  grate  j  both  these  are  repre- 
sented at/. 

183.  When  the  furnace  is  in  use,  it  is  raised  on  a  stand, 
and  the  nozzle  of  a  pair  of  double  bellows,  twelve  inches 
long  and  ten  inches  wide,  brought  towards  the  aperture  in 
the  lower  piece,  but  not  inserted.    The  fire  is  lighted  by  a 
piece  of  brown  paper  and  a  little  small  coal,  and  is  sustained 
either  with  coke  and  small  coal,  or  coke  alone.     The  coke  is 
sifted  of  two  sizes,  and  preserved  in  boxes,  with  a  ladle  to 
supply  it  to  the  fire.     When  a  fire  of  a  moderate  size  only  is 
wanted,  the  piece  b  is  used;  if  there  be  occasion  to  increase 
it,  c  is  put  on.     When  smaller  fires  are   required,  d  or  e  is 
used.     For  operations  where  tobacco-pipes  replace  ordinary 
crucibles,  the  grate  is  removed,  and  the  piece  and  plate  f 
placed  within  b  at  the  shoulder  g. 

Mr  Aikin  easily  melts  cast  iron  at  this  furnace,  and  can 
heat  a  crucible  two  inches  and  a  half  in  diameter,  and  three 
inches  and  a  half  in  height,  to  bright  redness  in  a  very  short 
time. 

184.  The  following  is  the  description  of  a  most  excellent 
blast-furnace,  which  has  been  in  use  for  some  years  in  the 
laboratory  of  the  Royal  Institution.     It  is  sufficiently  pow- 
erful to  melt  pure  iron  in  a  crucible,  in  twelve  or  fifteen  mi- 
nutes, the  fire  having  been  previously  lighted.     It  will  effect 
the  fusion  of  rhodium,  and  even  pieces  of  pure  platinum 
have  sunk  together  into  one  button  in  a  crucible  heated  by 
it.     All  kinds  of  crucibles,  including  the  Cornish  and  the 
Hessian,  soften,  fuse,  and  become  frothy  in  it ;  and  it  is  the 
want  Of  vessels  which  has  hitherto  put  a  limit  to  its  applica- 
tions.    The  exterior  consists  of  a  blue  pot  eighteen  inches 
in  height,  and  thirteen  inches  in  external  diameter  at  the  top. 
A  small  blue  pot,  of  seven  inches  and  a  half  internal  diame- 
ter at  the  top,  had  the  lower  part  cut  off,  so  as  to  leave  an 
aperture  of  five  inches.     This,  when  put  into  the  larger  pot, 


re 


POWERFUL  BLAST   FURNACE. 


105 


rested  upon  its  lower  external  edge,  the  tops  of  the  two  be- 
ing level.  The  interval  between  them,  which  gradually  in- 
creased from  the  lower  to  the  upper  part,  was  filled  with  pul- 
verized glass-blower's  pots,  to  which  enough  water  had  been 
added  to  moisten  the  powder,  which  was  pressed  down  by 
sticks,  so  as  to  make  the  whole  a  compact  mass.  A  round 
grate  was  then  dropped  into  the  furnace,  of  such  a  size  that 
it  rested  about  an  inch  above  the  lower 
edge  of  the  inner  pot :  the  space  beneath 
it  therefore  constituted  the  air-chamber, 
and  the  part  above  the  body  of  the  fur- 
nace. The  former  was  7i  inches  from 
the  grate  to  the  bottom,  and  the  latter 
7i  inches  from  the  grate  to  the  top. 
Finally,  a  horizontal  hole,  conical  in 
form,  and  1J  inches  in  diameter  on  the 
exterior,  was  cut  through  the  outer  pot,  forming  an  opening 
into  the  air-chamber  at  the  lower  part,  its  use  being  to  re- 
ceive the  nozzle  of  the  bellows  by  which  the  blast  was  to  be 
thrown  in.  The  furnace  being  thus  completed,  the  next  ob- 
ject was  to  dry  it  gradually,  that  when  used  it  might  not  be 
blown  to  pieces  by  confined  aqueous  vapour;  a  charcoal  fire 
was  therefore  made  in  it,  and  left  to  burn  for  some  hours, 
being  supplied  with  air  only  by  the  draught  through  the  hole 
into  the  chamber  beneath.  When  vapours  ceased  to  be 
formed,  the  furnace  was  considered  as  ready  for  use. 

185.  This  furnace  has  always  been  used  with  a  pair  of 
large  double  bellows  mounted  in  an  iron  frame,  the  former 
being  raised  upon  a  stool  so  as  to  bring  the  aperture  of  the 
air-chamber  to  a  level  with  the  nozzle  of  the  bellows.  The 
latter  has  generally  been  inserted  in  the  aperture;  for  this 
and  similar  furnaces  are  of  such  depth,  compared  to  their 
width,  that  when  charged  with  a  crucible  and  fuel,  there  is 
so  much  resistance  to  the  passage  of  the  air  when  urged  by 
a  blast  competent  to  create  and  sustain  a  vivid  combustion, 
that  a  part  returns  by  the  side  of  the  nozzle,  if  the  aperture 
be  left  open.  The  bellows  spoken  of  is  far  larger  than  ne- 
cessary for  the  furnace  described,  and  is  rarely  worked  to 
one-third  of  its  power ;  for  otherwise  the  heat  rises  so  high 
O 


106  SLAG  REMOVED THE  BLAST. 

as  to  destroy  the  crucible,  and  the  results  are  lost:  it  is, 
however,  at  all  times  advisable  to  have  an  abundant  com- 
mand of  air. 

186.  The  heat  produced  by  this  arrangement  is  such,  as  at 
every  violent  operation,  to  cause  the  production  of  some  slag 
from  the  melting  of  the  inner  surface  of  the  furnace  itself, 
where  the  combustion  has  been  most  vivid.     The  slag,  run- 
ning down  the  interior,  collects  round  the  edge  of  the  grate, 
and  should  be  removed  with  a  chisel  and  hammer,  or  with  an 
iron  rod,  after  each  operation,  that  the  grate  may  be  clear 
and    free    from    obstruction  for  the  next  process.     When 
in  the  course  of  time  the  interior  of  the  furnace  is  so  far  in- 
jured as  to  become  thin  and  weak,  it  must  be  displaced,  and 
the  furnace  restored  to  its  original  state,  by  the  introduction 
of  a  new  inside  as  before  (184). 

187.  The   fuel   to  be  used   in  this  furnace  is  coke.     Its 
consumption  is  very  small,  considering  the  heat  that  is  ob- 
tained, in  consequence  of  the  short  period  of  each  opera- 
tion.    The  superiority  of  the  blast-furnace  over  the  wind- 
furnace  in  many  operations  for  which  high  temperatures  are 
required,  depends  upon  the  rapidity  of  its  action.     It  is  re- 
quisite to  employ  this  furnace  in  the  open  air,  or  under  a 
well  arranged  vent,  for  an  immense  number  of  sparks,  much 
flame,  and  a  current  of  hot  air  are  produced  during  its  ope- 
ration, which  might  occasion  serious  mischief  in  a  room,  un- 
less the  ceiling  were  at  a  considerable  height,  or  guarded 
by  a  metal  screen. 

188.  In  using  a  blast  furnace,  like  the  one  described, 
some  circumstances  have  to  be  considered  relative  to  the 
method  of  applying  the  stream  of  air.     If  a  small  pair  of 
bellows  be  used,  the  nozzle  of  which  is  considerably  less 
than  the  aperture  into  which  the  air  is  propelled,  then  a 
much  larger  quantity  of  air  is  made  to  enter,  if  the  nozzle 
be  a  couple  of  inches  or  more  from  the  hole  on  the  outside 
than    if  it    be  actually  inserted ;    for  in   the    latter    case 
little  more  than  the  stream  of  air  from  the  bellows  is  thrown 
through  the  furnace,  whilst  in  the  former  a  large  additional 
quantity  is  propelled  and  drawn  by  the  advancing  stream 
and  carried  in  with   it  ;  just,  indeed,  as  happens  with  the 


FUEL COAL COKE.  107 

blow-pipe  jet  of  air  where  the  flame  and  neighbouring  at- 
mosphere is  drawn  into  the  current  formed  by  the  propelled 
central  stream.  Hence  if  the  bellows  be  small  and  the 
fuel  not  too  compact,  advantage  may  be  taken  of  this  cir- 
cumstance, and  the  heat  more  highly  raised  and  sustained 
than  if  the  effect  in  question  were  unattended  to. 

189.  Priestley,  and  after  him  Lavoisier,  proposed  the  ap- 
plication of  oxygen  to  furnaces,  to  increase  the  rapidity  of 
combustion,  and  consequently  the  intensity  of  heat :  but  it 
will  evidently  be  unnecessary  to  employ  it  whilst  furnaces 
in  which  common  air  is   used   continue  to  be  more  than 
equal  to  our  means,  in  consequence  of  the  limit  put  to  their 
application,  by  the  inadequacy  of  the  vessels  we  possess  to 
resist  higher  temperatures. 

190.  The/we/  to  be  used  in  furnaces  is  of  three  kinds, 
coal,  coke,  and  charcoal.     Coal  is  the  ordinary  fuel  for 
the  laboratory  table-furnace  (8 — 169),  or  that  intended  to 
be  in  use  every-day,  and  serve  for  fusions,  roastings,  and 
other  operations,  for  which  its  temperature  may  be  sufficient. 
It  is  very  desirable  that  it  should  be  good  of  its  kind,  and 
not  that  which  contains  much  sulphur,  or  an  abundance  of 
earthy  matter ;  for  the  first  interferes   with  various   fusions 
and  ignitions,  and  the  latter  renders  the  fire  dirty  and  dusty, 
and  when  the  temperature  is  raised  to  a  high  point,  causes 
an  abundance  of  clinkers.     On  certain  occasions,  to  be  here- 
after distinguished,  especially  if  the  coal   be  sulphureous 
and  bad,  it  may  be  necessary  to  use  both  coke  and  charcoal 
in  the  table  furnace.     Coal   should   never  be  used  in  the 
blast-furnace  :    for,    in   consequence    of  its  softening  and 
swelling  by  heat,  it  aggregates,  closes  the  small  channels 
by  which  the  air  finds  a  passage  through  the  fuel,  and  im- 
pedes the  combustion. 

191.  Coke  is  in  constant  requisition;  it  varies  in  quality 
with  the  coal  from  which  it  is  obtained.     Such  as  is  intend- 
ed for  the  service  of  the  blast-furnace  should  be  free  from 
sulphureous,  earthy,  and  metallic  matter. 

192.  On  the   contrary,  if  common  gas-coke  be  used  in 
this  furnace,  the  oxide  of  iron  and  earthy  matter  which  it 
contains  is  so  abundant  that  slag  is  soon  produced,  which, 


108  TEMPORARY  FURNACES. 

flowing  over  the  crucible,  corrodes  and  destroys  it ;  by  mix- 
ing with  the  fuel,  it  tends  to  prevent  the  access  of  air  to  its 
surface,  and  by  accumulating  upon  the  grate,  at  last  so  far 
obstructs  the  entrance  of  air  from  beneath,  as  to  prevent  the 
attainment  of  a  high  temperature. 

193.  The    Staffordshire  coke  whren    used    in    the  blast- 
furnace   before   described    (184)   should    be    broken    into 
pieces  somewhat  larger  than  a  walnut,  that  it  may  sink 
down  in  the  fire  between  the  crucible  and  the  furnace,  pre- 
senting a  constantly  compact  body  of  firel   (673);  and  it 
should  also  be  sifted  or  screened  before  it  is  used,  to  re- 
move the  dust  and  small  particles,  which  otherwise  being 
mixed  with  it,  would  interfere  with  the  passage  of  the  air, 
by  stopping  up  the  small  vacuities  between  the  different 
pieces  of  fuel  as  they  lie  in  the  furnace. 

194.  The  charcoal  intended  for  laboratory  use  may  be-of 
the  ordinary  kind,  and  must  not  be  either  too  large  or  too 
small.     If  large  the  pieces  should  be  broken  down,  or  they 
will  be  unfit  for  use  in  the  crucible  furnaces,  for  which  it  is 
principally  intended.     Charcoal  is  a  quick  fuel ;  but  burn- 
ing with  facility,  a  small  quantity  of  it  can  be  easily  retain- 
ed in  a  state  of  regular  combustion';*  and  hence  in  cases 
where  but  little  space  intervenes  between  the  substance   to 
be  heated  and  the  side  of  the  furnace,  or  when  a  small  tem- 
porary fire  is   required   in   the  air,   it  is  very   convenient. 
Where   Staffordshire   coke   will   burn,  and   by  means  of  a 
blast  or  a  draught  of  air  will  give  sufficient  intensity  of 
heat,  it  is  very  superior  to  charcoal  in  duration.     Occasion- 
ally a  mixture  of  coke  and  charcoal  is  convenient,  since  it 
affords  a  combination  possessing  the  qualities  of  permanen- 
cy and  freedom  of  combustion. 

A  charcoal  box  is  almost  as  essential  to  a  laboratory  as 
one  for  coal,  and  should  have  its  appointed  place. 

195.  It  frequently  happens,  that  instead  of  a  regular  fur- 
nace  fire,  a  temporary   arrangement  is  much  more  advan- 
tageous; thus,  a  fire  of  pieces  of  charcoal  may  be  arranged 
upon  a  plate  of  iron  or  tin,  or  upon  a  piece  of  iron  wire- 
work,  and  be  far  more  applicable  than  one  in  a  furnace. 
Sometimes  an  iron  wire  basket,  like  a  common  mouse-trap 


DEFENCES   AGAINST  THE   HEAT.  109 

turned  upside  down,  is  very  useful,  and  affords  great  heat 
because  of  the  access  of  air  to  all  sides  of  it,  whether  urg- 
ed by  draught  or  bellows.  A  loose  iron  grate  and  a  few 
bricks  will  often  serve  to  arrange  a  powerful  little  furnace  ; 
but  these  temporary  arrangements  must  be  left  to  be  sug- 
gested by  the  wants,  and  applied  by  the  judgment,  of  the 
experimenter. 

196.  It  must  be  remembered,   that  all   operations  with 
furnaces  should  be  carried  on  in  safe  situations,  care  being 
taken  that  no  danger  be  incurred  by  the  ascent  of  sparks, 
flame,  or  hot  air  ;  by  lateral  vicinity  to  combustible  bodies ; 
or  by  standing  upon  an  unprotected  wooden  surface.     When 
from  peculiar  circumstances  a  small  furnace  is  necessarily 
placed  in  such  a  situation  that  danger  may  be  anticipated 
from  the  ascending  current  of  air,  the  latter  may  frequently 
be  rendered  harmless  by  fixing  a  plate  of  tin  over  the  fur- 
nace, so   as   to   break   the  current,  and  mix  the  hot  air  of 
which  it  consists  with  the  neighbouring  atmosphere.     Inju- 
ry  from    the  vicinity  of  a  heated  furnace  to  wainscoat,  a 
trough,  or  any  thing  destructible  by  heat,  may  almost  al- 
ways  be   prevented   by   interposing  a  bright  sheet  of  tin- 
plate  ;  the  heat  being  then  reflected  and  the  neighbouring 
body  kept  perfectly  cool  (1359). 

197.  When  small  furnaces  are  placed  upon  tables,  stools, 
or  trays,  a  brick,  or  a  piece  of  sheet-iron  or  tin-plate  should 
be  interposed,  according  to  the  mode  by  which  the  heat  is 
likely  to  be  communicated  (1357):  a  brick  or  tile   should 
be  used  in  cases  of  conduction,  metal  in  sheets  to  catch 
ashes,  and  bright  tin-plate  to  prevent  the  ill  effects  result- 
ing from  radiation.     When  a  permanent  furnace  is  erected 
in  a  room  which,  being  floored  with  wood,  is  to  be  convert- 
ed into  a  laboratory,  great  care  should   be  taken  that  the 
ash-pit  and  parts  adjacent  be  guarded  by  a  stone  flooring 
laid  down  for  the  purpose.     The  stones  should  be  bedded 
in  a  proper  manner  beneath,  that  no  injury  may  arise  should 
cracks  occur  in  them,  or  in  case  they  should  not  be  of  suf- 
ficient thickness  to  prevent  the  transmission  of  heat, 

§  2.  Lamps. 
198.  Lamps  may  be  considered  as  small  furnaces,  and  are 


110  LAMPS. 

very  economical  and  ready  sources  of  heat.  Nor  are  they 
deficient  in  temperature ;  for  the  intensity  of  heat  in  flame 
is  very  high.  Since  the  method  of  operating  on  small  quan- 
tities of  matter  has  been  practised  and  improved,  not  only 
has  the  heat  of  a  simple  unassisted  lamp-flame  been  taken 
advantage  of,  but  many  contrivances  have  been  practised  by 
which  it  has  been  powerfully  increased  and  more  beneficially 
applied. 

199.  Of  the  varieties  of  lamps  used  in  the  laboratory,  the 
most  useful  is  that  in  which  spirit  is  burned.     Spirit  lamps 
may  be  bought  at  the  instrument-makers,  and   are  to  be 
trimmed  with  a  cotton  wick  and  supplied  with  alcohol. 
When  in  combustion,  the  flame  though  pale  produces  in- 
tense heat,  as  may  be  proved  by  introducing  a  small  platinum 
wire  or  other  piece  of  filamentous  matter  into  it.     The  stu- 
dent should  in  his  first  practice  accustom  himself  to  the  in- 
troduction of  small  fragments  of  minerals,  metals,  and  other 
substances,  into  the  flame,  at  the  extremity  of  a  thin  wire, 
or  a  filament  of  asbestus  or  cyanite,  or  upon  a  narrow  slip 
of  platinum  foil.     He  will  thus  habituate  himself  to  various 
appearances,   obtain    a  knowledge  of  the  heating  power, 
and  learn  from  experience  at  what  part  of  the  flame  the 
highest  temperature  exists,  and  where  he  should  intersect 
it  when  he  wishes  to  obtain  a  more  moderate  but  more  ge- 
neral heat. 

200.  The  flame  of  alcohol  produces  no  smoke  or  fuligi- 
nous matter,  and  hence  a  great  and  constant  advantage  pos- 
sessed by  it.  If  a  platinum  capsule,  or  a  small  platinum  cruci- 
ble, be  held  in  the  flame  of  a  candle,  for  the  purpose  of  ap- 
plying heat  to  its  contents,  a  black  sooty  film  is  soon  depo- 
sited, which  from  its  great  radiating  power  occasions  the  loss 
of  heat,  and  prevents  that  elevation   of  temperature   which 
the  flame  otherwise  is  competent  to  produce.     But  held   in 
the  flame  of  a  spirit  lamp,  the  blackening  does  not  take 
place,  and  this  circumstance  is  one  great  cause  why  the  rise 
of  temperature  is  to  a  much  higher  degree  in  this  than  in 
the  former  instance.     If  a  candle  were  used  to  apply  heat 
to  the  exterior  of  a  glass  flask  or  retort,  the  carbonaceous 
matter  would  soon  accumulate,  so  as  to  obscure  the  vessel 


SPIRIT-LAMPS.  Ill 

and  hide  the  contents;  but  a  spirit  lamp  occasions  no  such 
obscuration,  and  at  the  same  time  that  heat  is  applied,  the 
utmost  facility  of  observing  the  substances  within  is  afforded. 

201.  Where  the  flame  comes  in  direct  contact  with  the 
substance  under  experiment,  the  advantages  are  equally  on 
the  side  of  the  spirit  lamp.     For  the  carbonaceous  matter, 
besides  interfering  as  above  described,  would  frequently 
have  an  injurious  chemical  effect ;  whereas  it  seldom  hap- 
pens that  the  water  and  carbonic  acid,  which  result  from 
the  combustion   of  alcohol,  produce  any  change  by  their 
contact. 

202.  The  place  of  greatest  heat  in  the  steady  flame  of  the 
spirit  lamp  is  just  within  its  summit.     The  substance  to  be 
heated,  when  it  will  bear  the  direct  contact  of  the  flame, 
should  be  as  small  as  possible,  consistently  with  the  power 
of  duly  observing  its  changes.     It  may  be  supported  by  a 
pair  of  delicate  platinum  forceps,  or  at  the  end  of  a  piece  of 
fine  platinum  wire  or  foil;  or  when  the  substance  will  admit 
of  splintering,  may  itself  be  the  extreme  end  of  a  sharp  splin- 
ter, and  will  then  require  no  other  support.     In  all  cases  the 
support  should  be  as  thin  and  delicate  as  possible,  that  the 
heat  may  not  be  conducted  by  it  from  the  substance  to  be 
examined,  or  the  flame  itself  cooled  by  contact  with  it.    Oc- 
casionally, especially  when  the  support  is  platinum  wire,  it  is 
advantageous  to  make  that  part  of  it  which  is  next  the  sub- 
stance as  hot  as  possible,  that  its  tendency  to  conduct  heat 
from  the  body  to  be  ignited  may  be  diminished.     This  is 
easily  done  by  holding  it  so  that  the  wire  shall  ascend  as 
it  were  up  the  side  and  just  within  the  verge  of  the  flame, 
still  supporting  the  body  to  be  heated  in  the  hottest  part;  or 
at  times  it  is  sufficient  to  let  the  support  descend  from  above, 
the  hot  air  from  the  flame  heating  the  part  next  to  the  sub- 
stance to  a  sufficiently  high  temperature. 

203.  When  a  larger  substance  is  to  be  heated  it  is  gene- 
rally best  done  by  putting  it  lower  down  in  the  flame  than 
the  hottest  point,  the  flame  being  made  to  divide  under  it, 
and  ascend  a  little  distance  on  all  sides.     In  this  way  a  small 
platinum  crucible  or  capsule  may  be  heated  red-hot  through- 
out; whereas,  if  put  at  the  summit  of  the  flame,  such  effect 


112  SPIRIT-LAMPS. 

would  not  be  produced  because  of  the  partial  exposure  of 
the  vessel  to  the  surrounding  air. 

204.  Platinum  foil  is  a  useful  accompaniment  to  the  spirit- 
lamp.     A  square   inch  of  its  surface  may  be  made  at  once 
red  hot.     It  may  be  readily  bent  into  any  convenient  form, 
so  as  to  supply  the  place  of  crucibles  and  capsules  for  small 
quantities  of  matter.     It  suffers  scarcely  any  change  by  heat, 
is  affected  by  few  bodies  except  sulphur  and  the   reduced 
metals,  and  withal  is  so  bad  a  conductor  of  heat  that  it  con- 
veys less  from  substances  lying  upon  it  than  any  other  metal, 
and  does  not  conduct  an  inconvenient  quantity  to   the   fin- 
gers (1353).     If  pieces  of  platinum  foil,  about  an  inch  or  an 
inch  and  a  half  in  diameter  or  width,  be   put  into   a  small 
mortar  and  pressed  upon  and  moulded  with  the  pestle,  they 
will  form  excellent  capsules  for  numerous  purposes  of  igni- 
tion (371).     These  may  be  supported  by  the  wire  holders 
(666). 

205.  Spirit-lamps  of  the  usual  size  will  give  a  flame  of 
any  height  less  than  two  inches,  the  wicks  being  of  twisted 
cotton,  usually  about  a  quarter  of  an  inch  in  diameter ;  but 
a  lamp  with  a  larger  wick  is  desirable   in  the   laboratory. 
One  made  of  copper,  with  a  burner  one  inch  long,  by  the 
third  of  an  inch  wide,  will  produce  a  flame  in  which  a  pla- 
tinum crucible  nearly  two  inches  in  diameter,  and  small  glass 
retorts,  may  be  heated  to  redness. 

206.  A  very  powerful  and  useful  spirit-lamp,  frequently 
supplying  the  place  of  a  furnace,  is  formed  by  making  an 

aperture  of  0.8  or  0.9  of  an  inch  by  l~ 
through  the  body  of  the  lamp,  and  fixing 
in  it  four  burners,  upon  Count  Rumford's 
principle,  each  of  a  length  equal  to  the 
width  of  the  aperture,  and  the  ^  or  ^  of 
an  inch  wide.  These  are  to  be  parallel  to  each  other,  and 
at  such  distances  as  to  have  five  spaces  or  air  ways,  the  two 
outer  being  half  the  width  of  the  inner.  These  burners  rise 
about  a  quarter  of  an  inch  above  the  lamp,  and  descend  as 
low  as  the  bottom  of  the  body,  being  fastened  in  the  aper- 
ture by  their  edges.  Each  burner  is  closed  beneath,  but 


SPIRIT-LAMP PHILLIPS'S.  113 

has  a  small  hole  into  the  lamp  as  a  passage  for  the  alcohol, 
thus  forming  as  it  were  a  part  of  the  lamp.  The  lamp  is 
supported  upon  four  balls  about  half  an  inch  in  diameter,  to 
allow  of  the  access  of  air  beneath  and  up  the  apertures  to 
the  flame.  The  alcohol  is  introduced  by  a  hole  in  the  upper 
surface  of  the  lamp,  which  is  usually  closed  by  a  screw;  and 
the  burners  are  trimmed  by  putting  down  each  a  doubled 
cotton  of  an  Argand  lamp  until  it  touches  the  bottom,  and 
then  cutting  it  off  about  the  eighth  of  an  inch  above  the 
top. 

207.  Such  a  lamp  is  very  powerful  when  applied  merely 
as  other  spirit-lamps  are  to  the  vessels  to  be  heated,  but  it 
becomes  still  more  effectual  in  heating  a  crucible  when  as- 
sisted by  a  chimney.     This  may  be,  as  usu- 
al, a   copper  cylinder,  resting  below  upon 
the  flat  surface  of  the  lamp,  and  either  level 
at  the  top  or  cut  out  into  three  or  four  large 
scollops.     Two  chimnies  are  useful,  of  an 
inch  and  three  qarters  in  diameter  each,  one 
about  three  and   a  half,  and  the  other  five 
inches  in   length.      Such   a    lamp,  besides 
having  the  power  of  heating  crucibles  and 
retorts,  is  easily  adjusted   in  any  convenient 
place,  soon  set  to  work,  and  as  soon  extin- 
guished ;  and  if  convenient,  only  one  or  two  wicks  may  be 
lighted  at  once,  those  which  are  not  employed  being  cover- 
ed up  by  the  caps  which  are  used  to  slip  over  the  burners  to 
prevent  evaporation  when  the  lamp  is  not  at  work. 

208.  It  would  be  improper  to  omit  mentioning  Mr  Phil- 
lip's spirit-lamp*,  the  advantage   of  which  consists  in  its 
ready  construction  in  any  place  and   by  any  person.     "Let 
a  piece  of  tin  plate  about  an  inch  long  be  coiled  up  into  a 
cylinder  of  about  three-eighths  of  an  inch  in  diameter,  and 
if  the  edges  be  well  hammered  it  is  not  necesssary  to  use 
solder.     Perforate  a  cork  previously  fitted  to  a  phial,  and 
put  a  cotton  wick  through  the  short  tin  tube,  and  the  tube 
through  the  cork  ;  the  lamp  is  now  complete,  and  will  afford 

*  Annals  of  Philosophy,  New  Series,  VII.  36. 


114 


PYROLIGNEOUS  ETHER SIMPLE  SPIRIT-LAMP. 


a  strong  flame,  taking  care  of  course  not  to  prevent  the  rise 
of  the  spirit  by  fitting  the  cork  too  closely." 

209.  All  these  lamps  should  have  caps  for  the  burners, 
to  prevent  the  evaporation  of  the  alcohol  when  they  are 
not  in  use.      Those  which  are  sold  in    the  shops  are  al- 
ways furnished  with  them.     The  large   spirit  lamp  above 
described  should  have  one    for  each  burner,  the  material 
being  tin  plate.     Mr  Phillips's  lamp  may  easily  have  a  cov- 
er made  for  it  by  a  little   piece  of  glass  tube  closed  at  one 
extremity. 

210.  Alcohol    is   the    fuel    burned   in   these  lamps,  and 
though  it  need  not  be  highly  rectified,  yet  the  stronger  it  is 
the  better.     The  spirits  of  wine  of  the  distillers,  or  doubly 
rectified  spirit,  is  sufficiently  good  for  the  purpose,  the  spe- 
cific gravity  of  which  is  about  0.84  or  0.85. 

211.  There  is  a  substance  produced  in  considerable  quan- 
tity, during  the  destructive  distillation  of  wood,  called  by 
Mr  Taylor,  Pyroligneous   ether.     It  is  more  volatile  than 
alcohol,   but  burns  very  well  in  a  spirit-lamp.     It  has  a 
peculiar  odour,  but  in  consequence  of  its  cheapness  has  an 
advantage,  its  price  being  only  sixteen  shillings  per  gallon. 
It  may  be  obtained  either  at  Apothecaries  Hall,  or  at  No. 
201,  Strand,  but  is  inquired  for  and  sold  at  both  places  by 
the  name  of  Naphtha  as  often  as  by  its  proper  name.     This 
confusion  of  terms  is  very  improper,  for  Naphtha  and  Pyro- 
ligneous ether  are  very  different  substances. 

[The  spirit-lamp  represented  in  the  cut  is  one  devised  by 

the  Editor  six  or  seven  years 
ago,  and  since  that  time  has 
been  constantly  used  in  his 
laboratory  for  table-heat.  It 
is  made  of  tinned  iron.  The 
alcohol  is  poured  in  or  out 
by  means  of  the  hollow  handle, 
and  is  admitted  into  the  cylindrical  burner  by  two  or  three 
tubes  which  are  placed  at  the  very  bottom  of  the  foun- 
tain. By  such  an  arrangement  of  parts  the  alcohol  may  be 
added  as  it  is  consumed,  and  the  flame  kept  uniform; 
and  as  the  pipes  which  pass  to  the  burner  are  so  remote 


RETORT-STAND OIL-LAMPS. 


115 


from  the  flame,  the  alcohol  never  becomes  heated  so  as 
to  fly  off  through  the  vent-hole,  and  thus  to  cause 
greater  waste  and  danger  of  explosion.  Lamps  with  two 
or  three  concentric  burners  produce  a.  very  powerful  heat. 
A  very  great  heat  is  producible  by  bringing  up  through 
the  axis  of  the  burner  a  bellows  blow-pipe,  and  urging  the 
flame  vertically.  By  such  means  glass  tubes  of  an  inch  or 
two  in  diameter  may  be  sealed  or  blown  into  bulbs,  and  a 
platinum  crucible  heated  to  a  bright  yellow  heat. 

The  retort-stand  is  formed  of  sheet   iron  with  horizontal 

slits  for  the  support  of  shelves 
of  the  same  metal.  The 
shelves  are  perforated  by  tri- 
angular or  irregular  hexangu- 
lar  apertures,  which  give  to 
circular  vessels  a  steady  sup- 
port and  permit  the  free  pas- 
sage of  flame  -or  heated  air. 
This  retort-stand  is  convenient 
because  of  the  great  facility 
of  elevation  or  depression  of 
the  vessels,  and  the  ease  with  which,  they  may  be  removed 
along  with  the  shelf,  either  for  examination,  agitation  or  any 
other  purpose. — ED.] 

212.  Oil  is  a  fuel  so  applicable  in  the  service  of  lamps, 
and  also  so  economical  as  compared  to  alcohol,  that  oil- 
lamps  must  not  be  omitted  in  the  enumeration  of  sources  of 
heat.  Such  as  are  constructed  upon  Argand's  principle, 
having  circular  wicks  with  a  current  of  air  both  inside  and 
outside,  are  most  valuable.  They  are  now  constantly  con- 
structed for  laboratory  service,  the  material  being  copper, 
and  the  chimney,  in  place  of  glass,  being  also  of  that  metal. 
Their  principal  use  is  in  distillations  or  evaporations,  for 
they  possess  the  advantages  of  yielding  a  nearly  uniform 
heat  for  several  hours  together,  and  allowing  its  increase  or 
diminution  within  certain  limits  at  a  moment's  notice  (439, 
448,  465).  It  sometimes  happens,  that  the  highest  tempera- 
ture, or  greatest  quantity  of  heat  of  which  these  lamps  are 


116  DOUBLE-WICK  LAMPS. 

capable,  cannot  be  attained,  because,  notwithstanding  the 
careful  and  regular  manner  in  which  they  have  been  trim- 
med, one  part  of  the  flame  will  smoke,  if  the  wick  be  turned 
as  high  as  the  rest  of  the  flame  will  bear,  without  smoking. 
Upon  examination,  it  will  generally  be  found  that  the  part 
which  smokes  is  that  coinciding  with  the  notch  by  which 
the  arm,  connecting  the  cotton  ring  with  the  rack,  descends; 
in  which  part  the  cotton  is  necessarily  more  exposed  than 
elsewhere.  Should  it  be  so,  the  fault  is  easily  corrected 
for  the  time,  by  placing  a  little  slip  of  copper  or  tin  plate 
against  the  cotton  in  that  place  ;  and  then  the  other  parts 
may  be  raised  so  high  as  to  give  their  full  combustion  with- 
out smoke. 

213.  Double  concentric-wick  oil-lamps  have  been  con- 
structed for  the  purpose  of  permitting  greater  combustion 
and  supplying  more  heat.  These  frequently  fail  in  their 
applications,  and  generally  because  both  cottons  being  at- 
tached to  one  rack,  which  is  necessarily  placed  considerably 
on  one  side,  there  is  great  irregularity  of  action,  and  too 
much  friction,  whence  the  lamp  soon  becomes  deranged, 
and  is  rendered  useless.  This  evil  is  readily  corrected  by 
having  two  racks,  the  second  being  attached  to  the  dou- 
ble cotton  ring  exactly  as  the  first  is,  but  on  the  opposite 
side ;  and  then  with  care  the  lamp  may  be  arranged  with 
accuracy,  producing  as  much  heat  as  may  be  required  for 
crucible  operations  (666).  The  racks  should  be  raised  or 
lowered  regularly  and  equally,  so  that  both  may  assist  in 
moving  the  cotton  ;  and  care  should  be  taken  that  one  be 
not  raised  without  the  other,  or  the  one  made  to  pull  against 
the  other.  In  reference  to  the  wicks  also,  more  care  is  re- 
quired with  the  double  than  the  single  lamps,  in  consequence 
of  the  difficulty  of  trimming  the  two  cottons,  so  that  the 
flame  of  one  shall  not  have  a  greater  tendency  to  smoke 
than  the  other.  The  best  method  is  to  cut  them  as  seldom 
as  possible,  but  instead,  to  allow  them  to  burn  regularly, 
and  when  extinguished  and  cold,  to  remove  the  hard  crust 
and  leave  the  singed  edge  of  the  cotton  that  will  then  be 
exposed,  as  undisturbed  as  possible.  A  careful  attentive 
experimenter  will  in  this  way  find  no  difficulty  in  keeping 
a  double-wicked  lamp  in  order,  and  will  obtain  all  the 


GAS-LAMPS BLOW-PIPES.  117 

benefit  which  it  is  capable  of  affording  ;  whilst  a  hasty  care- 
less operator  will  never  be  able  to  make  the  cottons  move 
easily,  or  burn  without  smoke,  or  obtain  any  advantage 
from  the  lamp  over  an  ordinary  one. 

214.  It  is  essential  in   these   oil-lamps  that  an  abundant 
supply   of  air  to  the  wick  be  allowed.     As  generally  con- 
structed,  there  is  seldom  sufficient   air-way,  especially   in 
those  with  double  wicks  ;  and  though  they  may  burn  mode- 
rately well  at  first,  yet  the  accumulation  of  oil  and  dust  soon 
interferes   by  stopping  up   the   narrow  apertures,  and  thus 
manifests  the  deficiency.     It  is  advisable  to  use  the  best 
lamp  oil ;  for  the  constancy  and  steadiness  of  its  flame,  and 
brilliancy  of  the  combustion,  more  than  compensate  for  the 
higher  price  of  the  fuel. 

215.  The  erection  of  gas-works  for  public  service  is  now 
so  general  in  most  large  towns  and  in  numerous  private  es- 
tablishments, that  the  chemical  gas-lamp,  which  a  few  years 
ago  was  a  mere  curiosity,  has  now  become  a  valuable  and 
economical   auxiliary  to   the  establishment  of  the   chemist. 
The  facility  of  management,  and  the  regularity  of  flame,  are 
even  greater  than  with  the  Argand  oil-lamp,  for  by  means  of 
jointed  or  flexible  tubes,  in  conjunction   with  the   smallness 
of  the  burner  from  which  the  flame  proceeds,  as  compared 
with  the  body  of  an  oil-lamp,  it  can  be  adjusted  with  the 
utmost  nicety  in  any  required  position.     The  kind  of  flame 
depends  upon  the  form  of  the  burner.     A  single  jet,  or  a 
series  of  jets  in  aline,  or  a  circular  flame,  or  several  concen- 
tric flames,  may  be  obtained  at  pleasure,  and  thus  the  appli- 
cations of  the  gas-lamp  to  distillation,  the  igniting  of  cruci- 
blesj  &c.,  may  be  made  to  surpass  in  number  and  effect  those 
of  the  lamps  already  described.     It  is  only  requisite  to  have 
burners  of  the  different  forms  required,  capable  of  being  at- 
tached by  a  ground  joint  to  the  gas-pipe,  which  has  been 
laid  down  from  the  works. 

§  3.  Slow-pipes. 

216.  The  blow-pipe  is  an  instrument  which  cannot  be  dis- 
pensed with  in  the  laboratory  ;  and,  as  is  usually  the  case  in 
contrivances  for  the  attainment  of  any  particular  object,  the 


118 


BLOW-PIPE COMMON  VARIETIES. 


most  common  is  the  most  valuable.  The  chemist  does  not 
possess  a  more  ready,  powerful,  and  generally  useful  instru- 
ment, than  the  mouth  blow-pipe,  and  every  student  should 
early  accustom  himself  to  its  effectual  use  and  application. 

217.  The  forms  which  have  been  given  to  this  instrument, 
and  the  materials  of  which  it  is  constructed,  are  very  various. 
All  that  is  essential  is  a  tube  to  conduct  the  air  from  the 
mouth,  terminated  by  a  small  regular  round  aperture,  by 
which  the  air  can  be  thrown  out  in  an  undisturbed  stream ; 
and,  that  facility  may  be  obtained  in  directing  it,  the  lower 
end  of  the  instrument  is  generally  turned  to  one  side. 

218.  The  common  blow-pipe  is  a  long  conical  brass  tube; 
two  or  three  inches  of  the  narrow  end  being  bent,  so  that  the 

termination  is  nearly  at  right  angles  to  the  other  part 
of  the  instrument.  In  consequence  of  the  gradual 
condensation  of  moisture  from  the  breath  in  the  tube, 
when  the  instrument  is  much  in  use,  a  small  portion 
of  aqueous  matter  is  sometimes  ejected  through  the 
beak  into  the  flame,  and  upon  the  substance  to  be 
heated.  This  occasions  an  irregular  flame,  and 
sometimes  does  harm  to  the  heated  substance,  and 
the  blow-pipe  is  therefore  improved,  by  having  a 
chamber  constructed  at  one  part  of  it  for  the  recep- 
tion of  such  moisture  ;  the  accumulated  water  being 
removed  after  the  experiments  are  over.  Dr 
Black's  blow-pipe  is  a  conical  vessel,  close, 
except  at  the  summit,  to  which  the  mouth 
is  applied,  and  at  a  lateral  aperture  below, 
from  which  a  small  pipe  proceeds,  termi- 
nating in  the  nozzle  or  jet.  This  cone 
serves  not  merely  to  condense  the  mois- 
ture, but  in  a  slight  degree  to  regulate  the 
pressure  of  the  air  forced  through  it  by  the 
lungs  and  mouth.  Dr  Wollaston's  instrument,  on  the  con- 
trary, has  no  chamber,  but  consists  of  two  or  three  pieces  of 
tube,  which,  when  arranged  together,  form  an  excellent 
blow-pipe,  and  when  dismounted,  pack  into  the  size  of  a 
small  pencil-case. 


BLOW-PIPE JET TEMPORARY.  119 

219.  The  essential  part  of  the  blow-pipe  is  the  jet  or  ter- 
mination by  which   the  air  is  thrown  out.     The  aperture 
should  be  a  smooth  round  hole,  not  leading  suddenly  inwards, 
to  an  irregular  cavity,  but  enlarging  in  an  uniform  manner, 
so  as  to  form  a  small  regular  conical  channel,  at  least  the 
third  of  an  inch  in  length,  gradually  passing  into  the  general 
air-way  of  the  instrument.     The  exterior  should  also  be  re- 
gular in  its  form,  and  diminish  by  degrees  to  the  aperture ; 
that  when  a  stream  of  air  is  forced  through  the  blow-pipe, 
the  external  air  surrounding  the  jet  may  coalesce  gradually 
with  the  current,  and  not  have  the  motion  communicated  to  it 

disturbed  by  any  external  irregularities  of  form.  Per- 
haps the  best  model  for  a  jet  is  that  obtained  by 
drawing  out  a  piece  of  cylindrical  glass  tube  (1176), 
and  cutting  it  off  so  as  to  leave  an  aperture  of  a  pro- 
per size  ;  the  nearer  those  which  are  made  of  metal 
approach  to  this  in  form,  the  better  they  will  act.  The  size 
of  the  aperture  of  a  blow-pipe  must  depend  upon  the  flame 
to  be  urged,  and  the  substance  to  be  heated ;  for  ordinary 
use  it  may  be  one  fortieth  or  one  fiftieth  of  an  inch  di- 
ameter. 

220.  The  jets  of  blow-pipes  are  constructed  of  different 
substances,  those  being  in  this  respect  the  best  which  are 
made  of  materials  least  liable  to  change.     For  this  reason, 
and  also  because  of  the  facility  with  which  differently  sized 
apertures  may  be  used,  they  are  frequently  made  in  separate 
pieces  from  the  instrument,  and  arranged  to  slip  on  to  the 
extremity  at  pleasure.     From  the  small  quantity  of  metal 
required  in  their  construction,  they  may  then  be  made  of 
platinum;  and  a  conical  form  given  to  them  closely  approach- 
ing that  of  the  model  before  mentioned.     The  single  objec- 
tion to  jets  with  these  delicate  terminations  is  the  facility 
with  which  they  are  altered  in  form  and  injured :  but  it  is 
only  the  careless  who  surfer  in  this  way,  for  no  one  ac- 
quainted with  the  value  of  the  instrument  will  voluntarily 
subject  it  to  mechanical  injury. 

221.  When  a  blow-pipe  is  not  at  hand,  a  very  excellent 
temporary  one  may  be  made  from  glass  tube.     A  piece,  nine 
or  ten  inches  in  length,  and  about  one-third  of  an  inch  in 


120  MOUTH  BLOW-PIPE — USE  OF. 

diameter,  is  to  be  drawn  out  in  the  spirit-lamp,  so  as  gra- 
dually to  diminish  in  size  (1176,  1181),  and  then  to  be  cut 
with  a  file,  that  its  extremity  may  imitate  the  jet  before 
figured.  It  is  afterwards  to  be  softened  and  bent  on  one 
side  (1154),  about  two  inches  above  the  jet,  and  thus  a  per- 
fect instrument  for  the  time  will  be  obtained.  It  is  unfor- 
tunately brittle,  and  the  jet  is  liable  to  fuse  and  become 
closed  in  the  flame  when  the  current  of  air  is  suspended ; 
otherwise  it  would  supersede  most  of  the  common  blow- 
pipes. 

222.  The  first  point  to  be  acquired  in  the  use  of  the  blow- 
pipe is  the  practice  of  the  mouth.     It  is  easy  by  blowing 
through  the  tube  in  the  usual  manner,  to  produce  a  current 
of  air,  which  if  directed  upon  a  lighted  candle,  will  occa- 
sionally produce  a  clear  and  regular  jet  of  flame.     But  this 
operation  will  soon  be  found  uncertain  and  fatiguing,  and 
recourse  must  be  had  to  the  action  of  the  mouth  and  its 
muscles,  not  only  to  regulate,  but,  at  intervals,  to  perform 
the  whole  office  of  supplying  air  to  the  instrument. 

223.  The  practice  necessary  at  first  is  that  of  making  the 
mouth  replace  the  lungs  for  a  short  time,  by  using  no  other 
air  for  the  blow-pipe  than  that  which  it  contains.     This 
practice  is  simple  in  itself  and  soon  becomes  easy,  but  is 
difficult  to  describe.     Let  the  student  observe  that  it  is  easy, 
after  having  closed  the  lips,  to  fill  the  mouth  with  air,  and 
to  retain  it  so,  at  the  same  time  that  respiration  may  be 
freely  carried  on,  the  air  passing  to  and  from  the  lungs  by 
the  nostrils.     The  mouth  then  resembles  a  close  but  dis- 
tended bag,  and  the  means  being  well  observed  by  which  it 
is  thus  for  a  time  rendered  independent  of  the  lungs  and 
nostrils  as  to  air,  let  a  blow-pipe,  with  a  small  aperture,  be 
placed  between  the  lips,  and  then  again  filling  the  mouth 
with  air,  let  it  be  separated  as  before  from  the  lungs :  let 
the  respiration  be  carried  on  as  in  the  former  case,  but  at 
the  same  time  let  the  capacity  of  the  mouth  be  contracted 
by  the  action  of  the  muscles  of  the  cheeks  and  jaws,  and 
the  air  which  it  contained  propelled  through  the  blow-pipe. 
If  the  aperture  be  small,  this  operation  will  require  ten  or 
fifteen  seconds,  and  being  repeated  a  few  times,  a  ready 


BLOW-PIPE  PRACTICE.  121 

facility  of  using  the  blow-pipe,  independently  of  the  lungs, 
will  thus  soon  be  acquired. 

224.  This  step  being  taken,  the  next  is  to  combine  this 
process  with  the  ordinary  one  of  propelling  air  directly  from 
the  lungs  through  the  mouth  in  such  a  way  that,  when  the 
action  of  the  lungs  is  suspended  during  respiration,  the  blast 
may  be  continued  by  the  action  of  the  mouth  itself  from  the 
air  contained  within  it.     The  mouth  at  this  time  represents 
the  going  fusee  of  a  chronometer,  which  causes  the  works 
to  advance  during  the  interval  that  the  direct  action  of  the 
spring   is   taken    off,   by  the    hand   which   holds    the    key 
when  the  machine  is  wound  up  for  the  renewal  of  motive 
power.     The   time  of  fourteen  or  fifteen  seconds,  during 
which  the  mouth  can  supply  air  independently  of  the  lungs, 
is  far  more  than  that  requisite  for  one  or  even  many  inspi- 
rations ;  and  all  that  is  required  to  complete  the  necessary 
habit  is,  the  power  of  opening  and  closing  the  communica- 
tion between  the  mouth  and  the  lungs,  and  between  the 
lungs  and  the  air,  at  pleasure. 

225.  The  capability  of  closing  the  passages  to  the  nostrils 
is  very  readily  proved ;  every  one  possesses  and  uses  it  when 
he  blows  from  the  mouth  ;  and  that  of  closing  or  opening  the 
mouth  to  the  lungs  may  be  acquired  with  equal  readiness. 
Applying  the  same  blow-pipe  to  the  lips,  as  before,  use  the 
air  in  the  mouth  to  produce  a  current,  and  when  it  is  about 
half  expended,  open  the  lungs  to  the  mouth  so  as  to  replace 
the  air  which  has  passed  through  the  blow-pipe ;  again  cut 
off  the  supply  as  at  first,  but  continue  to  send  a  current 
through  the  instrument,  and  when  the  second  mouthful  of 
air  is  nearly  gone,  renew  it,  as  before,  from  the  lungs.     In 
this  way  acquire  the  power  of  using  the  air  of  one  inspira- 
tion by  mouthfuls,  as  it  may  be  termed,  not  at  any  time  let- 
ting the  air  from  the  lungs  press  upon  that  passing  through 
the  blow-pipe,  except  for  the  short  intervals  during  which  it 
is  being  renewed  in  the  mouth ;  but  measuring  it  out  as  it 
were  in  successive  portions,  and  giving  the  muscles  of  the 
cheeks  and  jaws  the  work  of  propelling  it  forward.     This 
advance  made,  then,  as  the  last  step  necessary,  learn  to  fill 


122  BLOW-PIPE ITS  USES. 


the  lungs  whilst  the  mouth  is  independent  of  them,  and 
occupied  in  propelling  the  air ;  and  this  cannot  be  difficult 
for  many  minutes  to  those  who  have  already  done  the  same 
thing  for  ten  or  fifteen  seconds  together,  as  just  described. 
Once  effected,  let  this  second  inspiration  of  air  be  used  as 
the  first  was,  and  in  the  course  of  three  or  four  inspirations, 
the  student  will  find  no  further  difficulty  in  understanding 
the  succession  of  actions  which  are  necessary  to  the  pro- 
duction of  a  continued  stream  of  air,  and  in  performing  them 
either  separately  or  in  order,  as  may  be  required. 

226.  The  description  of  these  processes  is  necessarily 
tedious,  and  the  performance  of  them  for  the  first  time  la- 
borious and  tiresome.     The  pupil  should  not  endeavour  in 
these  trials  to  produce  a  strong  current  of  air,  as  that  occa- 
sions unnecessary  fatigue.     The  smallest  stream  is  as  effi- 
cient as  a  larger  one.     The  art  once  obtained,  it  will  be 
quite  unnecessary  in  actual  practice  to  repeat  the  effects  in 
the  order  they  have  been  described.     The  peculiar  action 
of  the  mouth  is  not  necessary  to  a  continued  stream  of  air, 
except  as  connecting  the  air  of  one  inspiration  with  that  of 
the  next,  and  continuing  the  current  whilst  the  experimen- 
ter is  inhaling  ;  that  effected,  the  mouth  need  not  be  resort- 
ed to,  except  for  peculiar  purposes,  until  fresh  air  is  wanted, 
and  inhalation  again  necessary. 

227.  In  fact,  however,  the   mouth,   besides  continuing, 
regulates  and  modifies  the  blast ;  and  the  muscles  belong- 
ing to  it,  being  more  powerful  than  those  which  command 
the   lungs,   are   competent  to  the  production  of  a  much 
stronger  stream  of  air.     This  upon  occasion  is  very  useful 
and  important.     The  action  of  the  mouth  frequently  helps 
to  sustain  and  regulate  the  propelling  force  of  the  lungs, 
and  frequently,  also,  when  a  stream  of  air  for  a  long  period 
of  time  is  required,  the  mouth  is  advantageously  used  to 
propel  and  continue  it  whilst  four  or  five  inspirations  are 
made  :  the  lungs  are  thus  relieved  and  refreshed,  and  this 
being  repeated  from  time  to  time,  takes  from  the  operation 
a  great  portion  of  its  labour. 

228.  The  powers  of  the  blpw-pipe  will,  in  the  laboratory, 
frequently  be  added  to  those  of  the  spirit-lamp,  especially 


BLOW-PIPE FUEL FLAME,  123 

in  the  heating  of  capsules,  small  platinum  crucibles,  platinum 
foil,  glass  tubes  (666),  &,c.  But  when  a  very  intense  heat 
over  a  small  extent  only  is  required,  it  would  appear  that 
other  fuel  than  alcohol  is  better  for  the  purpose.  A  tallow 
or  a  wax-candle,  or  an  oil-lamp,  with  a  wick  about  three- 
tenths  of  an  inch  in  diameter,  affords  a  very  convenient 
flame.  Sometimes  the  wicks  of  lamps  are  made  broad  and 
flat,  for  the  purpose  of  supplying  a  greater  body  of  flame 
when  required. 

229.  The  lamps,  if  such  be  used,  being  trimmed  so  as  to 
occasion  their  full  ordinary  combustion,  the  jet  of  the  blow- 
pipe is  to  be  placed  in  a  horizontal   position   opposite  the 
flame,  about  the  eighth  or  tenth  of  an  inch  above  the  wick  ; 
and  a  steady  blast  of  air  being  thrown  from  it,  it  will  be 
found  that  the  flame  loses  its  ordinary  form  and  appearance, 
and  is  projected  as  a  luminous  pencil  along  the   course  of 
the  stream  of  air.     It  should  be  steady,  constant,  and  noise- 
less, not  quivering,  uncertain,  or  roaring.     A  small  propor- 
tion at  its  commencement  should  be  brightly  luminous,  but 
soon  pass  into  a  clear  blue  conical  flame,  towards  the  end 
of  which  on  the  exterior,  another  should  begin  to  appear  of 
a  pale  lambent  yellow  colour,  and  continue  to  an  inch  or 
more   beyond  the  termination  of  the  blue  flame  prolonging 
the  cone.     The  end  of  the  blue  flame  should  be  round,  well 
defined,  and  even  sharp  in  its  outline.     As  the  jet  is  ad- 
vanced  towards,  or  into,  or  withdrawn  from  the  flame,  so 
does  the  latter  vary  in  its  size,  shape  and  steadiness;  and  as 
the  power  of  changing  it  is  useful,  the  extent  to  which  it 
may  be  carried  should  be  ascertained  and  practised. 

230.  If  a  candle  be  used,  it  should  be  snuffed,  but  notshort, 
the  wick  inclined  a  little  on  one  side,  and  the  current  of  air 
from  the  jet  sent  obliquely  upwards.     If  sent  horizontally, 
the  heat  soon  melts  the  tallow  or  wax  on  the  side  beneath 
the  flame,  and  causes  it  to  run  down.     The  candle  will  fre- 
quently require  snuffing,  and  should  never  be  allowed  to 
have  any  useless  wick.     The  disadvantage  of  oil-lamps  is, 
that  they  also  require  frequent  trimming,  and  in  that  res- 
pect are  not  so  convenient  as  candles. 

231.  The  lamp  or  candle  should  be  low,  that  whilst  using 


124     BLOW-PIPE POWERS  OF  THE  PARTS  OF  THE  FLAME. 

the  blow-pipe  the  arms  may  rest  steadily  upon  the  table. 
The  hand  should  lay  hold  of  the  instrument  as  far  from  the 
mouth  as  convenient,  greater  freedom  of  motion  and  steadi- 
ness being  thus  obtained,  and  the  left  or  the  right  hand 
should  be  used  indifferently.  It  should  be  the  constant  en- 
deavour of  the  student,  when  he  is  using  the  instrument,  to 
obtain  the  power  of  so  apportioning  his  breath,  and  of  re- 
taining the  instrument  and  the  flame,  that  the  latter  shall 
appear  like  a  fixture,  and  neither  change  in  appearance  nor 
direction  for  several  minutes  together;  yet  this  with  such 
lightness  of  touch  and  easy  hold,  that  he  may  at  pleasure 
send  the  flame  in  any  direction  and  upon  any  place  he 
pleases. 

232.  The  point  of  highest  temperature  in  the  flame  is 
just  at  the  extremity  on  the  exterior  of  the  blue   cone. 
Here  the  combustion  is  complete  or  nearly  so,  and  has  suf- 
fered least  from  cooling  agencies  ;  but  there  are  other  parts 
of  the  flame  which,  because  of  their  peculiar  qualities,  de- 
mand a  few  distinct  observations.     Without  the  blue  flame 
combustion  is  complete ;  all  the  fuel  is  burnt  and  the  oxy- 
gen of  the  atmosphere  in  which  the  flame  is  formed  begins 
to  appear  in   excess,  and   from  thence  increases  outwards. 
Hence  the  power  of  oxygenation  to  a  great  degree,  in  con- 
sequence of  the  elevation  of  temperature  and  the  free  oxy- 
gen existing  there.     On  the  contrary,  within  the  blue  flame 
combustion  is  still  going  on,  consequently  combustible  mat- 
ter is  present;  there   is  no  free  oxygen,  and  a   reducing 
agency  is  exerted.     Berzelius  well  recommends  that  the 
situation  and  powers  of  these  parts  of  the  flame  should  be 
learned  by  operating  on  a  globule  of  tin  about  the  size  of 
a  shot  placed  in  a  small  cavity  on  charcoal ;  the  metal  will 
be  converted  into  a  white  crusty  oxide,  or  be  reduced  and 
appear  in  the  metallic  state  as  a  brilliant  fluid  globule,  ac- 
cording to  the  part  of  the  flame  directed  upon  it  and  the 
skill  of  the  operator. 

233.  When  the  temperature  required  is  not  particularly 
high,  but  the  substance  to  be  heated  is  large,  a  greater 
flame  is  to  be  used  (666).     It  may  be  obtained  from  the  al- 
eohol  lamp,  or  from  an  oil  lamp  with  a  flat  wick,  the  cur- 


A  ROARING  FLAME CRUCIBLE  HEATED .  125 

rent  of  air  being  directed  along  the  edge  of  the  cotton.  A 
jet  with  a  large  aperture  may  then  be  employed,  and  it  is 
occasionally  advantageous,  by  a  more  powerful  or  more 
abundant  blast  at  the  same  time  withdrawing  the  jet  a  little 
from  the  flame  (229,  245),  to  break  down  the  quiet  tranquil 
flame  into  a  roaring  one,^the  latter  having  power  to  heat  a 
greater  extent  of  surface  than  the  former.  A  crucible  or  a 
capsule  may  be  thoroughly  ignited  by  a  broken  flame ;  but 
the  same  instrument  and  lamp  with  a  steady  flame,  though 
they  will  heat  one  part  intensely,  would  leave  another  part 
comparatively  cold.  In  heating  a  glass  tube  for  the  pur- 
pose of  bending  or  blowing  it  out,  the  same  advantage  is 
obtained;  and  it  is  a  mistake  to  suppose  the  blow-pipe  is 
useful  only  for  the  purpose  of  increasing  and  concentrating 
heat,  it  being  in  the  laboratory  frequently  as  advantageous 
merely  for  directing  it.  When  the  mouth  blow-pipe  is  used 
with  the  large  spirit  lamp  before  described  (205),  a  platinum 
crucible  one  inch  and  a  half  in  diameter  may  be  heated  red 
hot  throughout,  and  a  glass  tube  of  considerable  thickness 
be  ignited  regularly  all  round  and  bent.  With  a  smaller 
lamp  or  a  candle,  the  blow-pipe  is  constantly  in  use  for 
melting  cement  or  other  fusible  bodies  upon  particular  parts 
of  apparatus,  or  warming  the  sides  or  tops  of  glass  vessels; 
and  it  is  for  these  amongst  other  purposes  that  the  power  of 
directing  the  flame  upwards  or  downwards,  or  in  any  direc- 
tion at  pleasure,  is  required. 

234.  The  current  of  air  is  hot  to  a  great  distance  beyond 
the  flame,  and  should  have  its  direction  and  power  well  ap- 
preciated by  observation  and  experiment.     It  is  frequently 
useful  in  warming  vessels,  and  the  student  will  best  learn  its 
capabilities  by  holding  pieces  of  paper  in  its  course,  at  dif- 
ferent distances  (1142). 

235.  The  theory  of  the  blow-pipe  is  simple :  its  powers 
depend  upon  the  perfect  combustion  of  the  fuel,  and  the 
rapid  succession  of  hot  gaseous  matter  against  the  substance 
to  be  heated.     The  force  which  propels  the  stream  of  air 
through  the  instrument  is  so  much  greater  than  the  ascend- 
ing force  of  the  heated  gaseous  products  of  the  combustion, 
that  the  currents  are  altogether  altered  :  the  surrounding 


126  THEORY  OF  THE  BLOW-PIPE. 

atmosphere  from  the  sides  and  behind  the  jet  of  the  blow- 
pipe, including  the  flame,  is  drawn  in,  and  made  to  coincide 
with  the  propelled  stream  of  air,  so  that  not  merely  is  the 
usual  form  and  direction  of  the  flame  destroyed  and  new 
ones  given  to  it,  but  with  such  power  that  the  ordinary  and 
fluctuating  motions  of  the  atmosphere  have  little  or  no  effect 
upon  it.  The  heated  particles  rapidly  succeed  each  other 
in  an  invariable  direction,  and  as  felates  to  the  position  of 
its  parts,  a  degree  of  permanency  is  thus  given  to  the  flame. 
The  point  at  which  the  particles  attain  their  highest  tempe- 
rature continues  the  hottest  so  long  as  the  current  is  un- 
changed, and  when  a  body  is  placed  there,  it  receives  the 
successive  action  of  these  particles,  and  is  itself  raised  to 
the  highest  possible  temperature.  By  far  the  greater  por- 
tion of  the  effect  is  due  to  the  circumstance,  that  the  mo- 
ment a  particle  of  flame  has  touched  the  body  and  been 
cooled  by  communicating  heat,  it  is  carried  off  by  the  cur- 
rent, and  replaced  by  other  particles  of  the  flame  at  a  maxi- 
mum temperature.  All  loss  of  heat  from  the  body  by  contact 
of  colder  particles  is  thereby  prevented,  and  the  elevation  of 
temperature  is  limited  entirely  by  the  temperature  of  flame, 
radiation,  and  the  deteriorating  effects  due  to  the  conduct- 
ing power  of  the  supports. 

236.  For  the  attainment  of  the  highest  possible  tempera- 
ture in  a  body  subjected  to  the  powers  of  flame  urged  by 
the  blow-pipe,  it  is  necessary  to  attend  to  other  circum- 
stances besides  choosing  the  hottest  place  in  the  flame.  It 
is  found  in  practice,  and  easily  explained  by  theory,  that 
within  certain  limits  the  smaller  the  particle  to  be  heated 
the  higher  will  be  the  temperature  acquired.  Hence  a 
reason  for  diminishing  the  size  of  the  piece  as  much  as  pos- 
sible. Then  the  supports  should  be  such  as,  presenting  the 
smallest  quantity  of  matter  by  which  the  heat  may  be  con- 
ducted away  or  otherwise  dissipated,  shall  still  resist  the 
high  temperature  necessary  to  be  borne  where  in  contact  with 
the  substance,  and  shall  also  exert  no  chemical  action  upon 
it,  or  at  least  none  that  can-  interfere  with  the  properties  to 
be  observed.  For  these  reasons  platinum  wire,  or  a  thin  slip 
of  platinum  foil  (204,  1353),  is  frequently  used  as  a  support; 


BLOW-PIPE SUPPORTS.  127 

and  forceps  are  constructed  with  delicate  terminations  of 
platinum  for  the  purpose  of  holding  such  solid  particles  as 
will  not  act  upon  them.  These  are  frequently  made  with  a 
pair  of  strong  steel  nippers  at  the  opposite  end,  to  break  or 
chip  off  small  splinters  from  minerals  or  brittle  bodies. 
When  a  thin  splinter  can  be  detached,  the  fine  edge  or 
point  is  frequently  more  favourable  for  high  ignition  than 
a  whole  fragment,  however  small,  supported  in  any  other 
way. 

237.  Mr  Smithson*  uses  small  plates  of  clay  as  supports 
for  substances  before  the  blow-pipe.     They  are  formed  by 
extending  a  white  refractory  clay  by  blows  with  the  ham- 
mer between  the  fold  of  a  piece  of  paper  like  gold  between 
skins.     The  clay  and  paper  are  then  cut  together  with  scis- 
sors into  pieces  about  four-tenths  of  an  inch  long  and  two 
and  a  half  tenths  of  an  inch  wide,  and  hardened  in  the  fire 
in  a  tobacco  pipe.     When  cut  into  small  and  very  acute 
triangles,  they  form  a  substitute  for  Saussure's  sappare.     The 
method  of  attaching  the  particle  to  be  heated  to  the  end  of 
these  strips,  or  what  is  perhaps  still  better,  to  the  end  of  a 
fine  platinum  wire,  which  has  been  since  adopted  by  Mr 
Smithson,  is  to  mix  a  very  refractory  clay  with  water ;  the 
least  quantity  of  this  is  to  be  taken  up  at  the  very  end  of 
the  clay  strip  or  the  wire,  and  the  particle  chosen  touched 
with  it :  in  a  few  moments  it  is  dry,  and  may  be  introduced 
into  the  flame  with  perfect  safety.     In  this  way  the  smallest 
observable  pieces  may  be  readily  experimented  with.    Some- 
times Mr  Smithson  makes  the  powder  of  the  substance  into 
a  mixture  with  water,  and  uses  it  instead  of  the  clay  for  attach- 
ing a  particle  to  the  end  of  the  wire. 

238.  Lieut.-Colonel  Tottenf  varies  these  methods  by  mak- 
ing the  pulverized  substance  into  a  paste  with  thick  gum-water, 
and  forming  it  between  the  fingers  into  small  acute  cones, 
the  fourth  or  fifth  of  an  inch  in  length.     When  dry  they  may 
easily  be  held  at  the  end  of  a  wire  or  in  forceps,  and  the 
apex  being  moistened  and  directed  to  the  particle  to  be  ex- 


*  Annals  of  Philosophy,  New  Scries,  v.  387.  vi.  412. 
f  Annals  of  Philosophy,  New  Series,  ix.  73. 


128  CHARCOAL-SUPPORTS. 

perimented  with,  adheres  to  it,  and  will  allow  it  to  be  subjected 
to  the  highest  heat  of  the  blow-pipe  without  suffering  de- 
rangement. 

239.  In  all  experiments  upon  minute  particles,  or  upon 
splinters,  it  will  be  necessary  to  examine  the  results  with  a 
glass,  and  not  to  trust  to  the  naked  eye.     Appearances  of 
fusion  or  porosity  will  frequently  escape  the  unassisted  eye. 
when  very  evident  under  a  lens. 

240.  When  charcoal  is  used  as  a  support  for  the  substance 
to  be  heated,  whether  for  the  sake  of  convenience  of  form,  or 
on  account  of  its  chemical  relations  to  the  body,  that  should 
be  chosen  which  has  been  made  from  young  succulent  wood, 
has  thin  bark,  and  is  without  cracks  or  cavities.    Alder  wood 
charcoal  is  by  far  the  best,  being  soft  and  generally  free  from 
divisions.     It  may  be  distinguished  by  the  triangular  form 
of  the  pith.     When  used,  a  little  cavity  may  be  made  with  a 
knife  on  its  convex  surface,  or  sometimes  even  at  the  end  of 
the  cylinder  where  the  cross  fracture  has  left  a  smooth  termi- 
nation, and  the  substance  being  placed  there,  the  flame  is  to 
be  sent  obliquely  down  upon  it.     Small  charcoal,  from  two- 
thirds  of  an  inch  to  an  inch  in  diameter,  is  most  convenient, 
because  of  its  easy  approximation  to  the  lamp  or  candle.    It 
would  be  difficult  to  send  the  flame  perpendicularly  into  the 
cavity,  nor,  if  it  were  easy,  would  it  often  be  desirable ;  for 
the  propelled  flame  would  return  upon  itself,  and  causing 
irregularity  in  the  stream,  would  fail  to  produce  the  usual 
temperature.     The  blast  should  be  generally  propelled  ob- 
liquely, that  the  flame  entering  over  one  side  of  the  cavity  af- 
ter having  struck  upon  the  matter  to  be  heated,  may  rebound 
a  little  and  pass  out  by  the  other. 

241.  For  ample  directions  in  the  management  and  use  of 
the  mouth-blow-pipe,  with  all  that  relates  to  the  characters 
and  tests  of  substances  examined  by  it,  the  student  is  referred 
to  Berzelius's  Essay-*;  which  being  essential  to  those  who 
would  apply  the  instrument  to  its  full  extent,  or  beyond  what 
are  its  ordinary  uses  in  the  laboratory,  renders  any  further 
account  of  it  here  unnecessary. 

*  Children's  translation  of  Berzelius,  on  the  use  of  the  blow-pipe,  8vo. 


TABLE   BLOW-PIPE.  129 

242.  The  next  useful  instrument  of  this  kind  in  the  labo- 
ratory, is  the  table  blow-pipe.     It  consists  of  a  small  table, 
furnished  beneath  with  a  pair  of  double  bellows  worked  by 
the  foot.     A  lube  is  connected   with   them,    which   rising 
through  the  table  is  made  adjustable  above  by  sliding  or  mov- 
ing joints,  and  terminates  in  a  jet.     This  jet  is  of  course  lar- 
ger than  that  of  the  mouth  blow-pipe,  being  intended  to  urge 
a  stronger  flame,  but  still  it  should  be  smooth  and  well  formed 
(219),  and  its  aperture  round  and  symmetrical.     It  is  almost 
always  the  work  of  the  instrument-maker,  but  when  a  tem- 
porary jet  is  required,  it  may  be  obtained  excellent  of  its  kind, 
by  drawing  out  a  piece  of  narrow  thick  green  glass  tube  in  the 
manner  before  described  (221).     The  lamp  (always  sold  with 
the  table,  though   separate  from  it)  should  have  a  burner 
competent  to  hold  a  bundle  of  twisted  cotton  half  an  inch 
thick  and  an  inch  wide,  the  top  of  the  burner  being  about 
two  or  three  inches  from  the  table,  that  the  jet  may  easily  be 
adjusted   to  any  required  position.     Tallow  or  dripping  is, 
perhaps  the  most  powerful  fuel  for  it;  but  in  the  laboratory, 
where  it  is  often  wanted  at  a  moment's  notice,  oil  is  the  most 
convenient. 

243.  After  having  trimmed  the  lamp,  leaving  the  cotton  in 
a  compact  wick,  rising  about  one-third  or  half  an  inch  above 
the  burner,  light  it,  and  place  it  on  the  table  before  the  jet ; 
then  sitting  on  a  chair  with  one  foot  on  the  treadle,  work  the 
bellows  slightly,  and  arrange  the  jet  by  moving  the  joints  of 
the  tube,  until,  being  horizontal,  or  nearly  so,  its  extremity  is 
a  little  above  the  cotton,  and  close  upon,  or  just  within,  the 
edge  of  the  flame.     The  force  of  the  blast  should  be  such  as 
to  gather  the  flame  and  make  it  proceed  in  the  same  direction 
with  the  jetj  without  any  upward  inflection  of  its  extremity. 
If,  for  want  of  power  in  the  jet  of  air,  this  be  not  at  first  at- 
tained, it  should  not  be  effected  by  working  the  foot  so  ra- 
pidly as  to  fill  the  bellows  and  drive  the  air  out  by  the  direct 
force  exerted  upon  the  treadle  ;  but  the  upper  board  of  the 
bellows  should  have  weights  placed  upon  it  in  such  quantity 
as  to  cause  pressure  sufficient  upon  the  air  within  to  make  it 
flow  out  with  the  required  velocity.     From  the  natural  rigi- 
dity and  tension  of  the  leather,  the  pressure  upon  the  inclu- 

R 


130  FLAME  OF  TABLE  BLOW-PIPE. 

ded  air  will  be  greater  when  the  bellows  is  nearly  filled  than 
when  almost  empty,  so  that  the  force  of  the  blast  may  be 
varied  by  keeping  the  bellows  more  or  less  full,  without  any 
alteration  in  the  loading  weight.  When  an  impulse  is  re- 
quired stronger  than  that  which  can  be  produced  by  the 
weight  and  tendency  of  the  bellows  to  collapse,  more  or  less 
direct  force  may  be  superadded  from  the  foot  by  means  of 
the  treadle. 

244.  The  pencil  need  not  necessarily  include  the  whole  of 
the  flame  rising  from   the  wick,  but  as  the  remaining  part 
throws  off' much  smoke  and  fuliginous  matter,  it  is  better  to 
conduct  these  substances  away  by  a  small  hood  and  chim- 
ney.    Such  an  arrangement  has  also  the  advantage  of  shad- 
ing the  bright  part  of  the  flarne  from  the  eyes,  in  conse- 
quence of  which  the  progress  of  operations  carried  on  in  the 
pale  part  are  much  more  readily  observed.     It  frequently 
happens  when  the  flame  of  the  lamp  is  too  large  for  the  jet, 
that  no  attempts  to    force  the  whole   into  a  clear  steady 
cone   will    succeed  ;   but  upon  advancing   the  jet  a   little 
way    into  the    flame,    a    part   will  be  thrown   forward   in 
the  greatest  perfection,  whilst  a  portion  behind  the  aper- 
ture will  rise  upright  in   its  usual  state,  and  almost  undis- 
turbed.    It  is  even  generally  advantageous  to  have  this  su- 
perabundance of  flame.     The   pencil  of  flame  should   be 
conical  and  steady,  not  ragged  or  broken,  but  ending  in  a 
blue  point,  passing  into  a  pale  phosphorescent  halo,  without 
any  luminous  or  smoky  part  at  the  termination. 

245.  Modifications  of  this  flame  are  required,  resembling 
those  described  as  useful  with  the  mouth   blow-pipe  (233). 
When  the  jet  is  withdrawn  a  little  way,  and  the  blast  impelled 
with  considerable  force,  the  flame   is   broken,  roaring,  and 
somewhat  diffuse  (229);  it  is  then   bluish,  burns  without 
smoke,  and  is  useful  in  heating  a  crucible  (666),  or  warming 
a  thick  glass  tube. 

246.  The  construction  of  a  temporary  blow-pipe  to  supply, 
in  cases  of  necessity,  the  place  of  a  table  instrument,  is  not 
difficult  (1207).     A  pipe  of  glass,  pewter,  or  any  other  sub- 
stance will  convey  the  air;  and   being  tied  to  a   weight  or 
stand,  or  even  a  candlestick,  may  be  arranged  at  the  proper 
height,  for  its  jet  to  accord  with  the  lamp  to  be  used.     The 


TEMPORARY  TABLE-RLOW-P1PE.  131 

first  rough  jet  may  be  made  by  drawing  out  a  piece  of  small 
glass  tube  in  the  spirit-lamp,  or  a  candle,  and  being  attach- 
ed to  the  apparatus,  a  second  and  proper  jet  may  be  made 
by  means  of  it,  out  of  a  thicker  piece  of  tube,  and  substitut- 
ed for  the  smaller  one  (221,  1181).  Instead  of  the  bellows 
a  large  bladder  may  be  used,  or  what  is  better,  a  bag  made 
of  oiled  silk,  or  some  of  those  fabrics  now  sufficiently  com- 
mon, in  which  cloth  is  rendered  air-tight  by  caoutchouc. 
This  may  be  placed  under  one  end  of  a  board,  with  weights 
upon  it,  or  within  a  portfolio,  subject  to  pressure,  and  the 
air  may  be  thrown  into  it  from  the  lungs  by  another  piece 
of  tube  sufficiently  long  to  reach  to  the  mouth.  This  tube 
will  require  a  valve  to  prevent  the  return  of  the  air;  and  the 
simplest  that  can  be  constructed  for  the  purpose,  in  an  ex- 
temporaneous manner,  is 'perhaps  the  following. 

247.  A  piece  of  any  lube  of  about  the  diameter  of  that 
represented  in  the  wood-cut,  having  a  smooth  and  level  end, 
is  to  be  selected,  and  also  a  strip  of  black  oiled 
silk,  of  a  width  rather  more  than  the  external  di- 
ameter of  the  tube,  or,  if  that  be  not  at  hand,  a 
piece  of  ribbon  of  the  same  width,  which  has 
been  rubbed  with  wax,  so  as  to  have  the  intersti- 
ces in  it  filled  up  without  destroying  its  flexibili- 
ty. This  is  to  be  adjusted  loosely  over  the  end 
of  the  tube,  and  the  extremities  folded  down  on 
opposite  sides,  and  tied  with  a  piece  of  thread;  the  silk  itself 
not  being  so  tight,  but  that  by  applying  the  mouth  to  the 
opposite  end  air  may  be  easily  blown  through  the  tube,  and 
out  at  the  extremity  between  it  and  the  silk;  and  yet  so  near 
that  a  pressure  being  exerted  in  the  opposite  direction,  the 
silk  will  be  carried  against  the  end  of  the  tube,  and  prevent 
the  air  from  passing  out  again.  The  tube  by  which  air  is  to 
be  thrown  into  the  bag  from  the  mouth,  is  to  have  such  a 
valve  constructed  at  its  extremity,  which  is  to  be  introduced 
through  a  hole  made  in  the  bag,  and  tightly  tied  in  it  by  a 
few  turns  of  twine.  So  arranged,  the  bag  is  easily  filled  by 
air  from  the  lungs,  which  being  gradually  expelled  at  the  jet, 
gives  energy  to  the  flame,  All  the  tubes  required  for  this 


132 


HARE'S  HYDROSTATIC  BLOW-PIPE. 


instrument,  except  the  jet,  may  be  made  even  of  paper,  in 
the  manner  hereafter  to  be  described  (1337). 

248.  A  lamp  for  such  a  blow-pipe  is  soon  fitted  up ;  a 
bundle  of  cotton  threads  placed  at  the  side  of  any  small  ves- 
sel filled  with  oil  will  answer  the  purpose,  and  none  is  more 
convenient  than  a  little  Wedgwood's  or  evaporating  basin. 

24,9.  The  pneumatic  blow-pipe  is  an  instrument  more 
portable  than  the  table  blow-pipe,  and  is  intended  to  sup- 
ply its  place.  There  is  nothing  relative  to  its  manipulation 
requiring  notice,  which  has  not  been  already  mentioned. 


250.  [The  wood-cut  represents  Professor  Hare's  hydro- 
static blow-pipe,  of  which  its  inventor  published  a  descrip- 
tion in  1802.  The  figure,  a  vertical  section,  is  so  expressive 
as  to  require  little  verbal  explanation.  It  consists  of  a  cask 
divided  by  a  horizontal  partition,  through  the  centre  of  which 
descends  a  pipe  for  the  passage  of  the  rod  which  works  the 
bellows  at  the  bottom  of  the  cask.  The  bellows  are  form- 
ed of  a  hollow  wooden  cylinder  surmounted  by  a  leather 


HARE'S  HYDROXYGEN  BLOW-PIPE.  133 

cover  nailed  to  the  wood,  but  left  large  enough  to  bulge 
either  way.  Two  valves,  one  at  the  bottom  of  the  bellows 
and  one  at  the  end  of  a  passage  which  passes  into  the  side 
and  out  at  the  top  of  the  cylinder,  regulate  the  direction 
of  the  air  when  the  bellows  is  worked.  A  pipe  for  the  in- 
troduction and  another  for  the  expulsion  of  the  air,  with  a 
treadle,  and  swivel-pointed  blow-pipe,  complete  the  appa- 
ratus, which  is  eminently  convenient,  and  as  readily  used  for 
the  application  of  other  insoluble  gases  as  for  that  of  com- 
mon air.  By  filling  such  an  instrument  with  oxygen  gas, 
and  bringing  from  a  reservoir  of  hydrogen  that  gas  into  con- 
nexion with  oxygen  just  before  its  exit  at  the  mouth  of  the 
blow-pipe,  Dr.  Hare  created  the  first  hydroxygen  blow- 
pipe.— ED.] 

251.  A  very  simple  and  powerful  method  of  increasing 
temperature,  the  application  and  advantages  of  which  were 
first  shown  by  Dr  Marcet*,  consists  in  urging  the  flame  of 
an  alcohol  lamp  by  a  blow-pipe  supplied  with  oxygen  gas. 
The  oxygen  may  be  furnished  from  an  air-holder,  a  gas 
bag,  or  any  other  vessel,  in  which  it  has  been  stored.     The 
flame  is  much  smaller  than  when  common  air  is  used ;  it  is 
also  brighter,  and  its  different  parts  have  not  the  same  re- 
lation :  for  instance,  when  the  flame  is  well  urged,  there  is 
no  point  in  which  an  excess  of  combustible  matter  can  be 
found,  or  where  deoxygenation  can  be  carried  on,  as  with 
the  common  blow-pipe  (232),  and  hence  it  is  never  put  to 
such  purposes ;    or  when  applied  to  them,  it  only  leads  to 
negative  or  deceitful  appearances.     The  hottest  part  of  this 
flame  is  very  near  the  mouth  of  the  jet,  the  distance  from  it 
being  not  more  than  one  third  or  one  fourth  that  occurring 
when  the  same  lamp  is  urged  by  common  air  (232).     The 
oxygenating  part  of  the  flame  (232),  is,  in  the  first  place, 
the  innermost :  then  there  will  usually  occur  a  part  where 
feebly  reducing  powers  reside,  and  on  the  outside  of  that  as 
before  an  oxygenating  atmosphere  again. 

252.  The  arrangement  called  Leeson's  blow-pipe  is  con- 
venient for  the  application  of  oxygen  gas.     It  is  a  bottle  of 
caoutchouc  or  India  rubber,  which  being  distended  with 

*  Thomson's  Annals  of  Philosophy,  ix.  21. 


134  LEESON'S — HARE'S. 

oxygen,  until  it  becomes  several  times  its  ordinary  diame- 
ter, is  then  to  be  attached  to  a  jet.  When  the  jet  is  op- 
posite to  a  flame,  and  the  stop-cock  opened,  the  contraction 
of  the  bottle  causes  a  regular  stream  of  gas  to  flow  out  for 
a  considerable  period,  and  an  intensely  hot,  but  small  pen- 
cil of  flame  is  obtained.*  Metallic  vessels  sufficiently  strong 
to  contain  several  atmospheres  of  oxygen  gas  have  been 
used  in  the  same  manner,  and  when  made  of  a  globular 
form,  small  and  air  tight,  are  very  pretty  and  convenient. 

253.  The  use  of  hydrogen  as  fuel,  instead  of  oil,  alcohol, 
&c.,   has   introduced   many  forms  of  apparatus  (some  of 
which  are  dangerous  to  beginners)  intended  for  the  special 
application  of  a  mixture  of  it  with  oxygen  gas.     Dr  Hare 
was  the  first  person  who  used   these  gases  in  conjunction, 
and  described  the  effects  produced.     He  sent  them  by  dif- 
ferent channels  to  the  aperture,  where  they  were  mixed  and 
burnt  at  the  same  instant.     There  was  no  danger  in  this  ar- 
rangement, and  the  manner  in  which  it  may  be  repeated, 
will  easily  be  understood  from  what  has  been  said,  and  the 
directions  to  be  given  relative  to  the  manipulation  of  gases. 
The  heat  was  very  intense. 

254.  In  consequence  of  the  experiments  made  by  Sir 
Humphry  Davy,  during  the  development  of  the  principles 
of  his  safety  lamp  and  researches  into  the  nature  of  flame, 
in  which  it  was  shown  that  the  flame  of  explosive  gaseous 
mixtures  would  not  pass  back  through  small  apertures  or 
tubes  ;  blow-pipes  were  soon  constructed,  in  which  the  oxy- 
gen and  hydrogen  being  mixed  in  the  proportions  necessary 
to  form  water,  were  then  compressed  in  metallic  boxes  to 
the  extent  of  many  atmospheres.     Small  tubes  were  after- 
wards affixed  to  these  boxes,  and  the  mixed  gases  being  al- 
lowed to  pass  out,  were  inflamed  and  burnt  at  the  apertures 
of  the  tubes.     Many  circumstances  combined  to  occasion 
accidents  with  this  apparatus.     The  tube  was  at  times  too 
large,  or  it  broke,  or  became  heated,  or  the  rapidity  of  the 
current  in  it  diminished  gradually,  and  the  flame,  retrograd- 
ing under  the  action  of  one  or  more  of  these  circumstances, 
ignited  the  mixture  in  the  reservoir  and  caused  explosion  : 

*  As  oxygen  gas  permeates  gum  clastic  with  some  facility  j  it  should  not  be 
long  kept  in  the  bag  before  it  is  used.— ED. 


PRECAUTIONS.  1  35 

and  notwithstanding  the  numerous  contrivances  invented  to 
prevent  this  return  of  the  flame,  there  is  not  one  I  believe, 
which  from  some  unperceived  or  uncertain  circumstance, 
either  in  the  principles  of  the  arrangement,  or  the  accidents 
to  which  it  is  liable,  has  not  failed  at  one  time  or  another. 
Hence  those  only  can  be  considered  perfectly  safe,  where 
the  reservoir  of  gas,  as  in  Dr  Clarke's  arrangement,  is  sepa- 
rated from  the  operator  by  a  wall  or  partition,  of  strength 
sufficient  to  give  full  security  :  and  those  are  next  perhaps, 
where,  as  in  the  arrangement  by  Mr  Gurney*,  the  gases 
are  confined  in  a  receptacle  so  slight  (a  bladder),  that  if 
blown  to  pieces  the  fragments  can  hardly  do  harm.  Then, 
the  only  liabilities  are,  that  the  explosion  itself  shall  shake 
and  injure  the  neighbouring  apparatus,  or  throw  them  about 
with  an  injurious  violence. f 

255.  There  are  still  some  points  in  the  economy  and  ap- 
plication of  heat,  which  require  attention  before  we  close 
this  section,  as  best  assimilating  with  its  subject  and  matter. 
These  principally  concern  the  modes  of  heating  by  interme- 
diate agents  ;  some  of  which  are  of  considerable  general  im- 
portance in  the  laboratory,  others  very  valuable  in  peculiar 
cases. 

256.  All  that  relates  to  the  general  construction  and  ar- 
rangement of  sand-baths  has  been  already  said  (169,  176), 
except  what  will  assimilate  with  the  processes  to  be  perform- 
ed on  them  (381).     Water-baths  resemble  sand-baths  in  of- 
fering a  medium  through  which  the  heat  can  be  applied  to 
the  substance  to  be  heated ;  but  differ  from  them  in  limiting 
the  heat  to  temperatures  below  a  certain  point,  and  when  re- 
quired, in  retaining  it  for  any  length  of  time  near  to  one  fixed 
degree,  that  of  212°.     This  temperature  is  important  in  the 
maceration  and  infusion  of  many  organic  substances,  for 
which,  though  a  greater  heat  would  be  highly  injurious,  the 
one  mentioned  is  desirable  and  even  necessary.    Water-baths 
are  generally  constructed  with  and  attached  to  the  vessels  in 
which  the  heating  operation  is  to  be  performed  ;  thus  in  the 

*  Transactions  of  the  Society  of  Arts,  xli.  70. 

f  Although  wire-gauze  placed  across  the  conducting  tube  gives  greater  se- 
curity, yet  an  explosion  has  occurred  where  several  different  pieces  have  been 
fixed  in  a  single  pipe.— ED. 


136  WATER-BATHS TUBE-BATH. 

carpenter's  glue-pot,  the  vessel  containing  the  glue  is  inserted 
in  another  containing  water,  the  latter  being  the  one  placed 
in  direct  contact  with  the  fire. 

257.  A  water-bath,  besides  regulating  and  equalizing  the 
heat  when  required  near  to  212°,  may,  from  the  liquidity  of 
the  medium  used,  have  its  temperature  ascertained  by  a  ther- 
mometer, and  consequently. regulated  by  attention   to  the 
source  of  heat.     Hence  it  offers  the  facility  of  raising  sub- 
stances in  closed  vessels  to  any  given  degree,  between  212° 
and  ordinary  temperatures  ;  thus  if  it  were  required  to  know 
at  what  point  a  certain  wax  or  a  new  resin  melted,  it  would 
only  be  necessary  to  put  a  piece  into  a  thin  tube,  and  the 
tube  with  a  thermometer  into  a  water-bath,   of  which  the 
temperature  was  gradually  raised,  and  moving  the  thermo- 
meter about  to  ascertain  the  temperature  of  the  bath,  when 
just  hot  enough  to  retain  the  substance  in  a  fused  state. 

258.  In  the  laboratory,  the  water-baths  are  generally  of 
extemporary  construction.     A  tin  or  copper  saucepan,  shal- 
low or  deep,  according  to  the  vessel  to  be  heated,  makes  a 
very  excellent  one.     The  immersed  vessel  should  not  touch 
the  bottom  of  the  bath ;  if  it  be  a  flask,  or  there  be  two  or 
three  to  be  heated,  some  hay  or  straw,  or  in  lieu  of  them  a 
little  tow,  should  be  placed  at  the  bottom  of  the  bath,  and 
the  flask  or  flasks  upon  it.     A  board  should  be  placed  across 
the  bath  with  holes  in  it  to  receive  the  necks  of  the  vessels, 
and  retain  them  upright  and  steady  :  or  even  straw  put  loosely 
into  the  vessel,  or  between  the  flasks,  will  answer  the  same 
purpose,  and  at  the  same  time  prevent  any  bumping  or  vio- 
lent ebullition  in  the  water  of  the  bath.     When  the  vessel  to 
be  heated  touches  the  bottom  of  the  bath,  heat  gains  access 
to  it  by  conduction,  the  temperature  is  no  longer  necessarily 
the  same  as  the  boiling  point  of  the  water,  and  may  at  times 
rise  so  high  as  to  do  considerable  injury. 

259.  An  evaporating  basin  frequently  answers  the  purpose 
of  a  water-bath,  and  the  substance  to  be  heated  may  also 
be  placed  in  a  small  basin  and  floated  on  the  water  in  the 
first.     A  glass  tube  will  often  form  a  water-bath  for  a  tube 
somewhat  smaller  (918),  and  frequently  when  the  aqueous 
vapour  would  interfere  it  is  prevented  by  making  the  bath- 
tube  the  shorter  of  the  two. 


WATER-BATH SOLUTION-BATH.  137 

260.  It  is  necessary  that  attention  be  paid  to  the  quan- 
tity of  water  in  the  bath,  that  it  may  not  be  so  far  diminished 
by  evaporation  as  to  occasion  injury  or  derangement,  either 
by  bringing  the  floating  vessel  into  contact  with  the  bottom, 
or  leaving  parts  of  the  bath  itself  uncovered.  It  is  often 
useful  for  many  reasons  to  put  a  little  oil  on  the  surface  of 
the  water  in  the  bath.  Suppose,  for  instance,  the  source 
of  heat  be  an  Argand  lamp  (212),  or  small  furnace  (158); 
as  the  temperature  rises,  evaporation  increases  so  rapidly, 
that  at  last  the  accession  of  heat  is  very  slow,  notwithstand- 
ing the  rapidity  of  combustion,  and  may,  at  times,  even 
be  limited  before  it  has  attained  the  boiling  point,  the  loss 
in  latent  heat  being  equal  to  the  gain  in  sensible  heat, 
A  film  of  oil  upon  the  surface  prevents  the  evaporation,  and, 
consequently,  the  loss  of  heat  hi  this  way,  and  the  tempera- 
ture rises  more  rapidly,  and  to  a  higher  degree  than  when 
the  water  is  uncovered.  If  it  be  required  just  below  212°, 
it  is  easily  retained  there  with  a  much  smaller  flame  or  fire 
than  would  otherwise  suffice,  the  water  is  not  liable  to 
diminution,  nor  will  it  require  watching  or  renewal,  and  the 
quantity  of  steam  given  off  is  comparatively  nothing ;  a  point 
of  some  importance  at  times  to  the  substance  in  the  inner 
vessel.  In  all  cases  when  heat  is  required  about  a  certain 
point  below  212°,  it  is  advisable  to  have  a  thermometer  bulb 
immersed  in  the  bath. 

261.  When  temperatures  above  212°  are  required  in  baths, 
pure  water  must  be  dismissed,  and  either  aqueous  solutions 
or  metals  used.  There  are  several  solutions  useful  for  these 
purposes,  which  boiling  at  different  temperatures  will,  of 
course,  communicate  heat  up  to  their  boiling  points.  A 
saturated  solution*  of 

Bitartrate  of  Potassa,  boils  at        .  214° 

Alum .220 

Borax 222 

Common  Salt       ....  224 

Tartrate  of  Potassa  234 

Muriate  of  Ammonia             •        .  236 

Nitre 238 

Rochelle  Salt       ....  240 

*  Quarterly  Journal  of  Science,  xviii.  90.    Griffiths. 


138  METAL-BATHS. 

If  a  particular  temperature  be  required,  234°  for  instance, 
it  may  be  obtained  in  two  ways  :  either  by  selecting  a  solu- 
tion which  when  saturated  boils  at  that  point,  as  one  of  tar- 
trate  of  potassa,  and  then  the  temperature  is  regulated  by 
the  process  of  ebullition  ;  or  a  sufficient  quantity  of  some 
other  salt  may  be  added  to  the  water,  so  as  to  form  a  solu- 
tion which,  though  not  saturated,  will  require  that  or  a 
higher  temperature  for  ebullition,  and  the  exact  point  may 
then  be  regulated  by  a  thermometer.  Rochelle  salt  and 
nitre  are  convenient  for  this  purpose,  the  temperature  being 
carried  by  them  as  high  as  238°  or  240°.  The  use  of  oil 
over  these  solutions  is  equally  advantageous  as  in  the  water- 
baths  (260).  Such  salts  should  be  selected  as  have  no  ma- 
terial action,  when  in  solution,  on  the  vessels  used,  and  are, 
at  the  same  time,  economical  and  effectual. 

262.  Solution-baths  will  produce  temperatures  up  to  360°, 
but  if  higher  temperatures  be  desirable,  recourse  must  ge- 
nerally be  had  to  metal-baths.     Solution-baths  are  advan- 
tageous for  digestion,  &c.,  carried  on  at  temperatures  above 
212°,  and  while  they  possess  the  useful  range  of  20  or  30 
degrees  above  that  point,  they  may  be  prepared  with  eco- 
nomy in  sufficiently  large  quantities.     Metal-baths,  on  the 
contrary,  are,  both  from  the  weight  and  expense  of  the  ma- 
terial, generally  on  a  small  scale,  and  their  principal  use 
consists  in  subjecting  substances  in  tubes  or  other  vessels 
to  a  given  or  an  increasing  temperature ;  or  in  ascertaining, 
by  the  gradual  application  of  heat,  which  may  be  measured 
by  a  thermometer,  at  what  point  any  particular  effect  is 
produced.     For  these  purposes  small  baths  are  as  effectual 
as  large  ones. 

263.  Mercury  is  the  substance  which  first  presents  itself 
for  these  uses :  it  may  be  applied,  with  care,  from  very  low 
temperatures  up  to  500°  or  600°.     If  the  experiments  be 
made  altogether  in  tubes  (259),  a  temperature  of  600°  may 
easily  be  communicated  by  means  of  it;  but  if  the  bath  be 
an  open  vessel,  a  dish  or  crucible,  for  instance,  then  tempe- 
ratures higher  than  450°  should  not  be  given  to  it ;  for  the 
metal  soon  after  rises  in  vapour,  and  the  fumes  not  only 
occasion  waste  of  mercury,  but,  at  times,  produce  injury 
both  to  the  experiment  and  the  health  of  the  operator. 


MODE  OF  ASCERTAINING  THE  TEMPERATURE.  139 

264.  For  temperatures  from  212°  and  upwards,  fusible 
metal  answers  the  purpose  admirably.     It  consists  of  8  parts 
of  bismuth,  5  of  lead,  and  3  of  tin,  fused  together.     It  melts 
at  a  heat  below  212°,  and  will  bear  a  red  or  even  white  heat 
without  evolving  fumes ;  but  at  dull  redness,  thick  films  of 
oxide  form  on  its  surface,  which  increase  with  its  temperature. 
Tin  or  lead  are  both  good  metals  for  temperatures  above 
their  fusing  points;  the  first  melts  at  441°,  the  other  at  009° 
Fahrenheit. 

265.  These  metallic  baths  may  be  used  in  glass  tubes  at 
temperatures  beneath  that  at  which  glass  softens  (918),  or 
in  evaporating  basins  up  to  temperatures  of  400°  or  500°, 
but  only  when  small.     When  large,  the  weight  of  metal 
would    endanger    both    the    vessel     and    the    experiment. 
Earthen  crucibles  are    convenient    for    the    immersion    of 
tubes  and  similarly  formed  apparatus,  but  whenthe  mass 
of  metal  required  is  great,  an  iron  crucible    or  pot,  or  a 
cast  small-iron  saucepan,  should  for  safety  be  resorted  to.^ 

266. -A  thermometer  may  be  employed  to  ascertain  tem- 
peratures as  high  as  650°,  but  it  should  be  open  above  for 
degrees  higher  than  580°,  as  will  be  stated  more  fully  in  the 
account  of  that  instrument  (290).  In  taking  the  temperature 
of  the  bath  the  thermometer  should  be  moved  in  the  fluid, 
for  the  purpose  of  equalizing  the  temperature  of  the  whole 
by  intermixture  (286),  as  much  as  possible;  and,  that  the 
tube  or  immersed  body  may  also  acquire  an  equal  tempera- 
ture with  the  bath,  it  should  also  be  moved  about.  A  little 
tallow  or  pitch  may  be  put  upon  the  surface  of  metallic  baths 
not  mercurial,  at  temperatures  below  700°,  to  prevent  the 
surface  from  oxidizing:  but,  at  higher  temperatures,  the  vo- 
latilization and  decomposition  of  these  bodies  would  oc- 
casion inconvenience.  If  a  bath  be  hot  and  covered  with  a 
coat  of  oxide,  the  latter  should  be  moved  on  one  side  with  a 
piece  of  card  or  stick,  at  the  moment  the  subject  to  be  heat- 
ed is  introduced,  otherwise  a  coat  may  intervene,  which  will 
tend  to  prevent  the  ready  transmission  of  heat. 

267.  The  operator  should  always  bear  in  mind  when  using 

*  Linseed  oil,  having  little  capacity  for  caloric,  and  bearing  a  temperature  of 
640°  F.  is  economical  for  baths  of  high  heat,-— ED. 


140  ALCOHOL  BATH — HOT  AIR. 

baths,  that  the  nature  of  the  substance  of  which  the  inner 
vessel,  or  that  containing  the  body  to  be  heated  is  composed, 
has  much  influence  over  the  transmission  of  the  heat.  It  is 
an  obstruction  through  which  the  heat  has  to  pass,  and  the 
obstruction  is  the  greater,  as  the  conducting  power  of  the 
substance  is  less.  If  a  substance  be  put  into  a  glass  tube, 
and  that  tube  immersed  in  a  water-bath  at  212°,  it  is  some 
time  before  the  contents  of  the  tube  will  also  acquire  212°. 
If  the  tube  were  of  metal,  its  contents  would  sooner  acquire 
the  ultimate  temperature,  because  of  the  superior  conduct- 
ing power  of  the  latter  substance  over  glass  (287). 

268.  There  are  occasions,  though  not  of  common  occur- 
rence, when  a  bath  is  wanted  that  will  not  permit  a  rise  of 
temperature  so  high  as  212°.     Thus  in  the  preparation  of 
euchlorine  from  chlorate  of  potassa  and  sulphuric  acid,  it  is 
prudent  to  heat  the  tube  retort  in  spirit  of  wine,  or  a  mix- 
ture of  alcohol  and  water;  for  the  temperature  not  rising  so 
high  as  with  water  alone,  there  is  less  probability  of  any  ac- 
cident with  this  explosive  gas. 

269.  Hot  air  is  an  excellent  heating  agent  on  many  occa- 
sions, in  consequence  of  the  facility  with  which  it  is  obtained 
and  conveyed  ;  it  therefore  claims  our  present  attention.     If 
it  be  convenient  to  procure  it  by  any  slight  alteration  about 
the  furnace  (169),  as  for  instance,   by  putting  a  cast-iron 
pipe  in  one  corner,  such  a  source  should  not  be  neglected, 
and  will  be  found  constantly  useful;  but  in  general  it  will 
be  more  advantageous  to  obtain  it  by  small  fires  or  lamps, 
the  whole  of  the  gaseous  produce  of  the  combustion  being 
employed.     A  shallow  charcoal  fire  in  a  small  crucible  fur- 
nace (158)   yields  an  abundant  supply  of  heated  gaseous 
matter.     A  piece  of  funnel  pipe  (165),  supported  on  a  tri- 
pod over  the  fire,  serves  as  a  channel  for  the  hot  stream 
which  may  be  conducted  upwards  or  thrown  right  or  left  by 
adjusting  pieces  (168),  as  may  be  required  :  and  the  tem- 
perature of  the  current  itself  may  be  regulated  within  cer- 
tain limits  by  placing  the  funnel  pipe  at  a  greater  or  smaller 
distance  from  the  furnace,  or  having  different  lengths  of  it, 
or  increasing  and  diminishing  the  fire.     Such  a  current  is 
useful  in  making  slow  distillations  or  rectifications  (439) ;  in 
heating  flasks  or  globes;  in  warmingelectrical  machines;  and 


STEAM-HEAT.  141 

the  fire  is  easily  renewed  or  arranged,  and  its  intensity  in- 
creased or  diminished  by  opening  or  closing  the  holes  to 
the  ash-pit  without  disturbing  the  apparatus  above. 

270.  Occasionally,  an  Argand  lamp  may  be  substituted 
for  the  charcoal  fire,  when  an  abundant  quantity  of  hot-air 
may  be  obtained,  by  supporting  a  plate  of  metal,  as  a  piece 
of  sheet  copper  a  foot  square,   about  an  inch  above  the 
chimney  of  the  lamp  (979).     It  breaks  the  current  of  heated 
gas  and  vapours  from  the  chimney,  becomes  hot  itself,  and 
heats  the  air  in  contact  with  it.     Such  an  arrangement  is 
very  useful  in  drying  papers  placed  over  it  (609),  or   in 
warming  an  electrical  machine.     Of  course  every  source  of 
combustion  for  such   purposes  should   yield' products  free 
from  smoke  or  fuliginous  matter. 

271.  Steam  is  in  many  situations  a  very  convenient  agent 
for  the  application  of  heat  up  to  temperatures  not  exceeding 
212°  Fahrenheit.     If  a  source  of  steam,  as  a  neighbouring 
boiler,  be  available,  nothing  more  is  requisite  than  to  con- 
duct the  steam  by  a  email  pipe  with  a  stop-cock  into  a  box 
or  vessel  containing  the  substance  to  be  heated.     A  tin 
saucepan,  for  instance,  will  hold  several  flasks  or  two  or 
three  retorts,  and  being  closed  by  a  cover,  having  holes  in 
which  to  adjust  the  necks  of  the  vessels,  the  passage  of 
steam  into  it,  in  sufficient  abundance/will  soon  heat  them  up 
to  212°. 

272.  If  a  steam  heat  be  indispensable  for  an  experiment, 
and  a  boiler  be  not  at  hand,  its  place  may  be  readily  sup- 
plied by  a  tea-kettle,  containing  about  a  pint  of  water,  or 
even  by  a  tin  can ;  pipes  to  convey  the  steam  a  few  feet,  if 
its  pressure    be  not  more    than   that  of  the    atmosphere, 
may  be  readily  made  of  oiled  cartridge  paper  (1337).  They 
should  be  an  inch  in  diameter,  formed  of  two  or  three  cir-.v 
cumvolutions  of  paper  tied  round  with  thread  or  twine,  and 
placed  in  an^inclined'position,  that  water  may  not  lodge  in 
them.     Such   pipes  should  [also  be  surrounded  by  a  loose 
case,  formed  by  wrapping  a  sheet  of  paper  round  them,  so 
as  to  make  as  it  were  an  external  tube,  at  least  half  an  inch 
larger  than  the  internal  one.     This  prevents  any  great  loss  of 
heat,  and  consequent  condensation  of  the  steam  within  them. 


URE'S  STEAM- HEATER. 

273.  Dr.  Ure  has  contrived  a  very  con- 
/TT3~zr5\  venient  apparatus  for  the  application  of  heat 
by  steam.  It  consists  of  a  tin  box  about 
eighteen  inches  long,  by  twelve  broad  and 
six  deep.  The  bottom  is  hollowed  a  little 
by  the  hammer  towards  its  centre,  in  which 
a  round  hole  is  cut  of  five  or  six  inches  in 
diameter.  Into  this  a  tin  tube  three  or  four  inches  long  is 
soldered.  This  tube  is  made  to  fit  tightly  into  the  mouth 
of  a  common  tea-kettle,  which  has  a  movable  handle.  The 
top  of  the  box  has  a  number  of  circular  holes  cut  in  it  of 
different  diameters,  into  which  evaporating  capsules  of  pla- 
tinum, glass,  or  porcelain  are  placed.  When  the  kettle 
filled  with  water,  and  with  its  nozzle  corked,  is  set  on  a 
stove,  the  vapour  playing  on  the  bottom  of  the  capsules, 
heats  them  to  any  required  temperature ;  and  being  itself 
continually  condensed,  it  runs  back  into  the  kettle  to  be 
raised  again  in  ceaseless  cohobation.  With  a  shade  above 
to  screen  the  vapour  chest  from  soot,  the  kettle  may  be 
placed  over  a  common  fire.  The  orifices  not  in  use  are 
closed  with  tin  lids.  In  drying  precipitates,  the  tube  of  a 
glass  funnel  may  be  corked  and  placed  with  its  filter  di- 
rectly into  the  opening  of  a  proper  size.  For  drying  red 
cabbage,  violet  petals,  &c.,  a  tin  tray  is  provided,  which  fits 
close  to  the  top  of  the  box  within  the  rim  which  goes  about 
it.  The  round  orifices  are  left  open  when  this  tray  is  ap- 
plied. 

274.  A  temporary  steam  bath  sometimes  readily  and  ad- 
vantageously supplies  the  place  of  a  water  bath.  Suppose 
it  were  required  to  evaporate  a  solution  at  temperatures  not 
higher  than  212°,  two  evaporating  basins  should  be  selected 
nearly  of  equal  size,  and  putting  water  into  the  smaller,  it 
should  be  placed  on  the  sand  bath,  or  over  a  lamp  or  fire, 
and  covered  with  the  larger,  into  which  the  solution  is  to 
be  introduced.  The  smaller  is  in  this  way  converted  into  a 
chamber  containing  water  at  the  bottom,  and,  when  heated, 
steam  at  the  top ;  the  steam  rises,  condenses  against  the 
bottom  of  the  upper  basin,  heating  it  and  its  contents,  and 


TEMPORARY  STEAM-BATHS.  143 

the  condensed  water  returns  back  to  that  below.  The  ex- 
cess of  steam,  if  there  be  any,  passes  out  at  the  side  where 
the  lip  of  the  basin  leaves  a  little  opening,  and  at  such  a 
distance  from  the  interior  of  the  upper  basin,  as  not  to  in- 
terfere with  the  concentration  of  its  contents. 

275.  In  other  cases  the  water  and  steam  bath  may  be  use- 
fully combined.     The  figure  represents  an  arrangement  in 

which  a  saucepan  is  converted  into  a  tem- 
porary steam  chamber.  Three  flasks  are 
arranged  in  it,  the  necks  appearing  through 
holes  in  a  tin  plate,  which  serves  as  a  cover, 
and  which  should  be  dished  a  little,  or  de- 
pressed in  the  middle.  Water  to  the  depth  of  an  inch  or  two 
is  to  be  put  into  the  saucepan,  and  when  the  vessel  is  placed 
over  a  little  charcoal  fire,  becomes  converted  into  steam, 
which  rising  and  coming  in  contact  with  the  flasks,  elevates 
them  and  all  within  the  vessel  to  its  own  temperature.  The 
water  condensed  on  the  under  surface  of  the  dished  cover 
trickles  back  to  that  at  the  bottom  of  the  vessel,  and  by  man- 
agement the  flasks  are  retained  for  any  time  at  a  tempera- 
ture of  212°,  with  very  little  escape  of  steam  or  evaporation 
of  the  water.  This  arrangement  is  frequently  more  conve- 
nient than  a  water-bath  made  deep  enough  to  receive  the 
whole  of  the  flasks,  because  of  its  lightness  and  the  superior 
steadiness  of  the  flasks,  from  their  not  being  buoyed  up  by 
any  quantity  of  circumambient  fluid.  A  similar  arrangement 
is  often  useful  for  distillation  or  rectification,  the  body  of  the 
retort  being  introduced  into  the  vessel  and  heated  by  the 
steam  which  rises  from  the  water  beneath. 

276.  Upon  occasions  of  refined  investigation  relative  to 
the  force  of  vapours,  or  the  conversion  of  liquid  bodies  into 
vapours  below  temperatures  of  212°,  or  even  as  high  as  240°, 
it  is  useful,  for  the  observation  of  the  immersed  apparatus, 
to  have  baths  of  water  or  solutions,  in  glass  jars  or  other  ves- 
sels to  which  the  fire  cannot  be  directly  applied,  and  which 
yet  require  to  have  their  temperatures  sustained  fora  certain 
period  of  time.     In  these  cases  the  end  is  best  obtained  by 
throwing  steam  into  the  bath  itself,  through  a  tube  descend- 
ing to  the  bottom  of  the  liquid.     Such  steam  must  be  ob- 


144  THERMOMETERS. 

tained  from  a  boiler,  because  of  the  pressure  of  fluid  it  has 
to  overcome ;  but  small  experimental  boilers  from  four  to  six 
inches  in  diameter,  that  may  be  placed  over  a  lamp,  are  suf- 
ficient. The  tubes  must  be  of  metal  or  glass,  not  of  paper. 
During  the  experiment  it  is  well  to  cover  the  bath  with  oil, 
to  prevent  loss  of  heat  by  evaporation  ;  and  also  to  wrap  it 
round  with  a  dry  cloth,  or  a  few  folds  of  paper,  when  it  is 
not  necessary  to  watch  the  changes  within  whilst  the  tempe- 
rature is  rising.  In  these  cases,  two  or  three  thermometers 
should  be  introduced  into  the  bath  to  detect  any  difference 
of  temperature  that  may  occur  at  different  parts  ;  for  where 
the  surface  is  so  large,  and  the  cooling  agencies  powerful, 
whilst  the  source  of  heat  is  confined  to  one  spot,  it  is  neces- 
sary that  great  care  should  be  taken  that  all  parts  of  the 
bath  agree  in  temperature. 

§  4.  Thermometers. 

277.  The  thermometer  being  an  instrument  in  constant 
use  for  ascertaining  temperatures  within  certain  limits,  it  is 
essential  that  the  student  should  be  made  acquainted  with 
the  errors  to  which  it  is  liable,  the  means  of  correcting  them, 
and  the  general  circumstances  by  which  its  indications  are 
influenced.  It  will  be  unnecessary  to  describe  the  method 
of  making  these  instruments,  for  in  consequence  of  the  gen- 
eral diffusion  of  chemical  science,  and  the  practice  of  chemi- 
cal a'rts,  they  are  constructed  and  circulated  in  such  quanti- 
ties in  commerce,  that  it  is  difficult  to  imagine  a  place  in 
which  such  pursuits  are  likely  to  be  carried  on,  where  they 
may  not  be  found.  Besides,  the  construction  of  a  thermome- 
ter, though  simple  in  theory,  is  difficult  in  practice.  It  re- 
quires great  tact  and  dexterity  to  produce  one  of  very 
moderate  goodness ;  and  without  steadily  watching  the  pro- 
cess as  performed  by  another,  or  previously  possessing  much 
practical  knowledge  in  glass-blowing,  &c.,  it  would  be  a 
vain  attempt  to  make  one  from  a  written  description.  Here, 
therefore,  we  shall  confine  ourselves  to  the  examination  and 
correction  of  instruments  which  are  made  by  others ;  and 
this  is  the  more  necessary,  since  ordinary  thermometers 
are  frequently  inaccurate,  sometimes  considerably  soy  and 


THERMOMETERS   EXAMINED.  145 

ould  often  lead  to  gross  errors  in  delicate  experiments, 
hough  sufficiently  correct  for  common  purposes. 

278.  The  most  usual  thermometer  is  that  which  contains 
ercury,  and  is  sealed  hermetically  at  the  top.     It  should 

not  include  air.  To  ascertain  whether  it  is  perfect  in  this 
respect,  invert  it,  and  by  a  short  sharp  shake  or  two  endeavour 
to  make  the  column  of  mercury  descend  in  the  tube.  If  but 
little  mercury  be  in  the  tube,  nearly  the  whole  being  con- 
tained in  the  ball,  it  may  be  difficult  to  effect  this  ;  it  is  then 
facilitated  by  warming  the  bulb  until  a  longer  column  is  pro- 
pelled into  the  tube,  when  the  shake  will  generally  cause  it 
to  descend.  As  the  mercury  moves  in  the  tube,  it  will  either 
leave  an  equivalent  void  space  in  the  bulb  above,  or  it  will 
part  in  the  tube  itself,  a  portion  only  of  the  column  passing 
downwards.  In  either  case  the  indication  with  regard  to  the 
presence  or  absence  of  air  in  the  tube  will  be  the  same,  for 
if  the  metal  traverses  the  whole  length  freely  and  descends 
to  the  extremity  or  nearly  so,  no  air  of  any  consequence  can 
be  present.  On  the  contrary,  if  it  passes  but  a  little  way 
down  the  tube,  air  is  present.  If  it  will  not  descend  at  all 
by  any  effort  that  can  safely  be  made,  air  may  be  suspected. 
When  air  is  present,  it  occasions  irregularities  in  the  indica- 
tions of  the  instrument,  which  can  only  be  accurately  ascer- 
tained by  comparing  it  experimentally  with  another  thermo- 
meter known  to  be  correct. 

279.  Supposing  no  air  to  be  present,  the  accuracy  of  the 
graduation  is  next  to  be  ascertained.     Thermometers   are 
generally  graduated  by  having  two  points  marked  upon  their 
stems,  corresponding  to  the  melting  temperature  of  ice  and 
the  boiling  temperature  of  pure  water  in  a  metallic  vessel 
under  the  pressure  of  the  atmosphere ;  and  the  intervening 
space  is  then  divided  into  a  certain  number  of  equal  parts, 
each  being  called  a  degree.     Of  these  there  are  180°  in 
Fahrenheit's  scale  and  100°  in  the  centigrade  scale.     If  the 
scale  is  to  be  continued  above  or  below  these  points,  it  is 
done  by  making  divisions  equal  in  length  to  the  degrees  thus 
ascertained.     To  try  the  accuracy  of  the  point  marked  32° 
Fahrenheit,  mix  some  pulverized  ice  or  snow  with  a  little 
water  so  as  to  make  a  thin  paste  ;  introduce  the  bulb  of  the 

T 


146 


( ;  R  A  D  U  AT  ION   CX  A 1VI I N  K 1 ) . 


.= 

50- 


40-1= 


2C- 


10-  = 


thermometer  into  the  mixture,  and  agitate  it  there 
for  a  few  minutes' until  the  mercury  is  stationary 
on  the  graduation.  If  it  accords  with  the  point 
marked  32°,  it  is  so  far  correct.  To  try  the  point 
212°  Fahrenheit,  put  some  distilled  water  into  a 
metallic  vessel,  into  which  also  introduce  the 
bulb  of  the  instrument,  holding  it  near  the  surface 
of,  or  in  the  water* ;  cover  the  vessel  and  make 
the  water  boil  so  as  to  yield  abundance  of  steam, 
the  barometer  being  at  the  same  time  at  30  in- 
ches, or  very  nearly  so  ;  observe  the  thermometer 
after  a  few  minutes,  when  it  has  attained  its  max- 
imum of  heat,  and  if  the  metal  correspond  with 
212°,  that  point  is  also  correct. 

280.  Finally,  to  ascertain  if  the  intervening 
degrees  are  equal,  and  in  that  respect  likewise 
correct,  separate  a  portion  of  the  column  of  mer- 
cury in  the  tube  of  one,  two,  or  three  inches  in 
length  from  the  rest,  by  inverting  and  jerking 
the  instrument  as  before  mentioned  (278);  bring 
it  to  different  parts  of  the  tube,  and  consequently 
of  the  scale,  by  inclining  the  instrument  more  or 
less  in,Various  directions,  and  by  tapping  it  if 
there  be  occasion  ;  and  observe  in  all  these  situa- 
tions whether  the  portion  of  mercury  so  separated 
occupies  the  same  number  of  degrees  :  if  rt  does, 
the  instrument  is  accurate  ;  if  it  does  not,  the  de- 
grees are  of  different  value  in  different  parts  of 
the  scale,  and  the  instrument  is  incorrect. 

281.  Should  it  be  found  impossible  thus  to  separate  a  small 
part  of  the  column  to  serve  as  a  test  of  the  scale  between  32° 
and  212°,  then  the  instrument  must  be  compared  with  one 
known  to  be  correct,  either  from  its  having  undergone  such 
trial,  or  from  having  been  formed  from  apiece  of  glass  tube, 
previously  examined  with  regard  to  the  equality  of  its  bore, 

*  In  the  case  of  immersion,  the  bulb  should  not  be  plunged  deeply,  because 
the  temperature  of  boiling  water  varies  with  the  depth.— ED. 


Til EKMOMETE11S  COMPARED.  147 

by  forcing  through  it  a  small  cylinder  of  mercury,  and  thus 
measured  in  different  parts  (1370).  If,  on  comparison,  three 
or  four  equidistant  points  prove  to  be  correct,  and  the  scale 
is  found  to  have  divisions  of  equal  length  in  all  its  parts,  then 
it  mny  be  considered  as  good. 

282.  The  method  of  ascertaining  whether    the   scale   is 
equally  divided,  is  io  lay  it  by  the  side  of  another  scale,  an 
inch  rule  for  instance,  and  observing  how  many  degrees  arc 
equal  in  extent  to  a  given  space  on  the  second  scale,  then  to 
move  it  up  or  down,  and  examine  whether  in  other  parts  the 
same  number  of  degrees  are  also  equal  to  the  same  space. 
The  student  should  understand  that  ascertaining  the  points 
of  32°  and   212°,  and   also  the  equality    in   length  of  the 
divisions  on  the  scale,  is  not  sufficient  to  ensure  the  accuracy 
of  the  instrument ;  since,  if  the  tube  be  conical  or  otherwise 
irregular  in  the  bore,  a  correct  graduation  would  give  de- 
grees unequal  instead  of  equal  in  length  (1370). 

283.  If  neither  32°  nor  212°  be  contained  on  the  scale  of 
the  instrument  to  be  examined,  then   it  must  be  verified  by 
trial  with  a  thermometer  known  to  be  correct,  and  three  or 
four  points  having  been  found  to  accord,  the  regularity  of 
the  divisions  must  be  examined  as  already  described  (282). 
If  one  of  these  two  important  points  be  included  it  should 
be  verified  as  before. 

284.  If  the  thermometer  to  be  examined  contain  alcohol 
instead  of  mercury,  there  is  no  opportunity  of  separating  a 
small  cylinder  of  fluid  to  measure  the  equality  of  the  divi- 
sion; or  of  ascertaining  the   point  of  212°  in  the  manner 
described  (279)r    That  of  32°,  and  three  or   four  others, 
must  then  be  ascertained  as  already  described  (281),  and  the 
equality  of  the  scale  observed  by  comparison  as  before  (282). 

285.  When   the  scale  passes   above  212°  or  below  32°, 
these  parts  are  examined  only  by  observing  that  the  degrees 
are  equal  in  bulk  to  those  between  the  two  points.     This 
equality  is  of  course  measured  by  the  little  cylinder  of  mer- 
cury, as  before  explained  (280). 

280.  In  all  experimental  comparisons  of  thermometers, 
essential  care  should  be  taken  that  time  be  allowed  them  to 
acquire  the  temperature  of  the  bath  in  which  they  are  in> 


148  THERMOMETER VARIATIONS  ,OF. 

mersed  ;  and  they  should  be  constantly  moved  about  in  it, 
and  made  to  change  places,  or  serious  differences  may  exist 
between  them  (266,  267).  A  large  and  a  small  bulb,  or  a 
mercury  and  spirit  thermometer,  will  take  different  periods 
to  heat  and  cool,  and  if  observed  hastily  may  not  only  be 
examined  whilst  of  different  temperatures,  but  also  whilst 
both  differ  from  the  liquid  in  which  they  are  immersed: 
treated  in  this  way  good  thermometers  may  seem  bad,  and 
more  harm  than  benefit  will  result  from  the  investiga- 
tion. 

287.  It  is  for  this  reason  that  trials  made  by  putting  a 
good  thermometer  and  the  one  to  be  examined  into  a  hot 
liquor,  and  observing  whether  they  sink  together  as  the 
temperature  falls,  are  often  fallacious.  If  the  thermometers 
be  dissimilar  in  bulk  or  some  other  circumstance;  if  the 
bath  be  small,  and  the  time  occupied  in  observing  the  fall 
of  several  degrees  be  short,  the  instruments  will  frequently 
appear  to  be  a  degree  or  two  different,  when,  if  properly 
examined,  they  would  prove  to  be  alike  ;  and  neither  of  them 
will  indicate,  during  the  process,  the  temperature  of  the 
bath  in  which  they  are  immersed.  It  is  easy  for  the  student 
to  gain  practical  proof  and  experience  of  the  extent  of  this 
effect,  by  taking  two  thermometers,  so  far  resembling  each 
other,  as  to  indicate  alike  when  immersed  in  the  same  bath, 
and  introducing  the  bulb  of  one  of  them  into  a  thin  tube 
with  a  little  mercury  in  it.  Upon  immersing  that  tube  in 
the  same  bath  with  the  uncovered  thermometer,  and  allow- 
ing the  heat  to  gain  access  to  the  instrument  through  the 
intervening  mercury  only,  he  will  find  on  comparing  the 
two  instruments  how  great  a  difference  will  be  occasioned 
between  their  indications,  as  the  temperature  of  the  bath 
rises  or  falls.  This  effect  is  due  to  the  thin  tube  and  the 
mercury  it  contains,  which  obstructing  the  passage  of  the 
heat,  retard  the  changes  of  temperature  in  the  thermometer 
itself  (267).  The  effect  varies  with  the  thickness  of  the 
glass,  and  the  quantity  of  metal,  and  illustrates  sufficiently 
the  differences  that  may  be  introduced  in  hasty  experiments, 
by  the  variable  thickness  of  the  bulb  and  quantity  of  mer- 
cury in  the  thermometers. 


CAUSES  OF  IRREGULAR  INDICATIONS.  149 

288.  There  are  some  causes  which  slightly  interfere  with 
the  permanency  of  the  indications  of  a  thermometer  ;  but 
they  are  of  a  delicate  nature,  and  need  not,  except  in  par- 
ticular cases,  be  attended  to.     It   is  said  that  the  constant 
pressure   of  the   atmosphere   on   the   exterior   of  the  bulb, 
gradually  alters  its  bulk,  rendering  it  smaller,  and  thus  ele- 
vating the  mercury,  and  causing   it   to  stand  higher  in  the 
scale  than  it  ought  to  do*.     It  is  also  said  that  a  thermome- 
ter, when  cooled  or  heated  considerably,  and  then  returned 
to  its  former  temperature,  does  not  immediately  give  the 
same  indication  that  it  did  before,  but  is  lower  than  it  should 
be  in  the  first  case,  and  higher  in  the  second,  from  the  tar- 
diness  with    which  the   glass  regains    its   original   bulkf. 
These  are  refinements  which  it  will  not  be  necessary  for  the 
student  to  consider,  until  he  has  advanced  so  far  in  the  sci- 
ence as  to  be  competent  to  enter  into  a  consideration  of 
their  presumed  effects.     All  that  will  be  necessary  is  to  try 
the  thermometers,  should  they  be  old,  to  ascertain  that  the 
graduation  corresponds  to  the  height  of  the  mercury,  and 
that  they  have  not  suffered  a  change  by  time  like  the  first  of 
those  referred  to.     If  any  opportunity  occurs  of  observing 
peculiar  changes  or  appearances,  it  will  be  proper  to  note 
them  for  the  illustration  and  explanation  of  those  presumed 
and  delicately  influencing  causes. 

289.  It  will  be  unnecessary  to  describe  the  peculiarities 
and  uses  of  all  the  varieties  of  thermometers.     No  other 
liquid  than  alcohol  and  mercury  is  now  used.     Ordinary 
alcohol  thermometers  must  not  be  employed  for  the  indica- 
tion of  temperature  above  180°,  for  if  subjected  to  higher, 
they  would  either  yield  wrong  indications,  or  burst;  but 
that  fluid  having  never  yet  been  congealed,  they  may  be 
applied  to  the  indication  of  exceedingly  low  temperatures. 
Mercurial  thermometers  may  be  used  for  temperatures  20 
or  30°  below  0°  or  up  to  500°  or  600°.     At  these  high  tem- 
peratures they  are  very  liable  to  vary  from  each  other  in 

*  Bihliotheque  Universelle,  xx.,  117. 

t  Giornale  cli  Fisica,  v.  26S.     Bid.  Universelle,  xxi.,  254,  xxii.,  265. 


150  MERCURIAL  THERMOMETERS. 

their  graduation,  for  want  of  an  unexceptionable  and  natural 
standard  point  by  which  they  can  be  corrected. 

290.  A  good  mercurial  thermometer,  hermetically  sealed, 
will  not  indicate  temperatures  higher  than  580°  (266),  for 
above  that  point  the  mercury  boils  in  the  bulb;  but  when 
open  at  the  top,  and  consequently  subject  to  the  pressure 
of  the  atmosphere,  it  will  indicate  temperatures  from  60°  to 
70°  higher.     If  wanted  for  delicate  experiments,  these  in- 
struments should  be  small,  not  merely  in  the  tube,  by  which 
the  divisions  are  rendered   larger  and  the  indications  conse- 
quently  more  minute,  but  in   the   bulb  also.     A  thermo- 
meter indicates  temperature,  by  taking  from  or  giving  to 
the  heat  of  the  body  to  be  examined,  until  on  an  equality 
with    it;    hence    the    body   changes    in    temperature   upon 
the    introduction    of  the    instrument,  and    if  it   be   small, 
whilst  the  thermometer  is  large,  the  heat  which  results  when 
they  are  both  alike,  may  be  considerably  different  from  that 
of  the  body  at  first.     This  would  cause  an  important  error, 
which  is  only  to  be  avoided,  or  rather  diminished,  by  using 
a  thermometer  so  small  that  it  shall  not  occasion  a  material 
change  in  the  temperature  of  the  substance  into  which  it  is 
introduced.     A  large  thermometer  is  also  longer  in  heating 
or  cooling  than  a  small  one,  and  may  from  the  lapse  of  time 
necessary  to  allow  of  its  proper  change,  occasion  an  altera- 
tion of  temperature,  by  allowing  the  body  tried  to  cool  or 
warm  (266).     Small  thermometers  are,  therefore,  frequently 
more  useful  and  accurate  than  larger  ones ;  and  in  order  to 
compensate  for  the  diminished  mass  of  mercury  whose  ex- 
pansion is  actually  measured  in  the  instrument,  and  to  pre- 
vent the  degrees  from  lessening  in  length  and  delicacy  with 
the  bulb,  the  tubes  are  usually  made  of  a  proportionably 
smaller  internal  diameter.     A  great  advantage  is  then  gained 
by  using  a  tube  with  a  flat  bore,  the  capacity  being  rendered 
very  small,  and   consequently   the  degrees   comparatively 
long,  whilst  the  surface  to  be  looked  at  is  large. 

291.  When  a  bulb  is  thin  or  large  and  the  column  of 
mercury  in  the  tube  long,  the  instrument  will  occasionally 
be  affected  in  its  indications  by  the  position  in  which  it  is 


THERMOMETERS — EFFECT  OF  SIZE.  If)? 

held.  Suppose  a  thermometer,  having  a  column  of  mercury 
of  15  inches  in  the  tube,  to  be  held  perpendicularly,  and 
afterwards  inverted,  and  the  bulb  held  uppermost:  if  the 
column  did  not  descend  or  part  in  the  latter  position,  there 
would  be  occasioned  a  difference  of  pressure  upon  the  ex- 
terior of  the  bulb,  equal  to  a  whole  atmosphere,  by  this  sim- 
ple change  of  position;  for  the  column  of  mercury  of  15 
inches  first  exerting  a  pressure  into  the  bulb  would,  in  the 
latter  case,  be  equivalent  to  an  equal  pressure  added  upon 
its  exterior.  It  is,  this  difference  of  pressure  which,  when 
sufficient  to  affect  the  bulk  of  the  glass  bulb,  causes  an 
apparent  difference  in  the  temperature  indicated  in  the  two 
positions.  It  will  therefore  be  advisable  to  try  the  instru- 
ment by  change  of  position,  to  be  aware  of  any  effect  of  this 
nature  to  which  it  may  be  subject,  and  which  of  course  will 
take  place,  although  in  a  smaller  degree,  with  any  depar- 
ture from  the  vertical  position. 

292.  Another  error,  occasionally  introduced  by  a  long 
tube,  depends  upon  the  variable  quantity  of  mercury  sub- 
mitted to  the  heat  at  the  time  of  graduation  and  the  time  of 
use.  If  a  thermometer,  with  a  tube  three  or  four  feet  long, 
be  graduated  by  immersion  of  its  bulb,  and  two  or  three 
inches  of  stem  only,  into  melting  ice  and  boiling  water,  and 
then  used  in  situations  where  the  greater  part  of  the  stem, 
as  well  as  the  bulb,  is  exposed  to  heat, — the  indications  may 
be  two  or  three  degrees  higher  than  the  temperature  to 
which  it  is  really  exposed.  A  thermometer  existed  at  Whit- 
bread's  brewery,  some  years  ago,  which,  belonging  to  a 
deep  evaporating  vessel,  passed  through  the  top,  and  de- 
scended perhaps  three  feet  before  the  bulb  entered  the  fluid; 
this  instrument  indicated  a  heat  in  the  boiling  wort  beneath 
some  degrees  higher  than  the  same  wort  brought  up  in  a 
bucket,  and  tried  by  another  instrument,  or  even  boiled  in 
a  smaller  vessel,  and  yet  examined  in  the  usual  way,  it  ap- 
peared to  be  correctly  graduated  :  the  difference  depended 
upon  the  expansion  of  the  mercury  in  the  stem  by  the  heat 
of  the  steam  above  the  liquor,  to  which  it  was  exposed  when 
in  use,  which  was  added  to  the  expansion  of  that  in  the  ball, 
the  only  part  heated  at  the  time  of  graduation. 


152  AIR  THERMOMETER. 

293.  Some  thermometers  are  formed  with   a  chamber  or 
bulb  in  the  upper  part,  so  that  if  accidentally  raised   to  the 
boiling  point  of  the  fluid  within,  the  fluid   and  vapour  may 
pass  into  this  space,  and  the  bursting  of  the   instrument  be 
prevented.     These  are  so  far  advantageous,  but  they  cannot 
be  made  free  from  air,  and  are  in  that  respect  inferior  to  the 
others. 

294.  Thermometers  should  not  be  introduced  suddenly 
into  hot  or  cold  substances,  for  then  the  glass  is  liable  to 
crack  at  the  stem,  and  the  instrument  consequently  be  de- 
stroyed. 

295.  The  graduation  of  these   instruments   is   sometimes 
made   on   the   glass,   and  sometimes  on   a  separate   scale. 
When  examined,  the  eye  should  be  brought  perpendicularly 
to  that  part  of  the  stem  where  the  mercury  stands,  so  as  to 
look  directly  through  and  on  each  side  of  the  tube,  that  the 
correct  coincidence  of  the  surface  with  the  scale  may  be  ob- 
served.    If  the  graduation  be  looked  at  obliquely,  through 
or  upon  the  tube,  the  apparent  places  of  either  the  mercury 
or  the  degrees  are  not  the  real  ones. 

296.  Although  accurate  graduation   has   been  thus  far 
spoken  of,  it  is  with  reference  only  to  the  mode  generally 
acknowledged  and  practised,  namely,  that  of  ascertaining 
the  freezing  and   boiling  points  of  water,  and  dividing  the 
interval  into  a  certain  number  of  equal  parts,  each  of  which 
is  called  a  degree,  and  used  as  the  model  for  other  degrees, 
made  upwards  or  downwards  on  the  scale.     Whether  such 
a  process  is  strictly  philosophical  is   not  the  question ;   all 
divisions  must  be  arbitrary,  and  that  adopted  has  the  essen- 
tial  quality  of  producing  instruments  strictly  comparable 
amongst  themselves. 

297.  Air  is  a  substance,  which,  though  not  in  general  use 
in  the  construction  of  thermometers,  is  adopted  in  peculiar 
trains  of  experiment ;  and  the  student,  when  engaged  in  con- 
sidering the  researches  of  Mr  Leslie  and  MM.  Petit  and  Du- 
long,  will  have  occasion  to  observe  the  valuable  uses  to  which 
these  philosophers  have  put  instruments  containing  it.     The 
simplest  air  thermometer  consists  of  a  thin  glass  bulb  at  the 
end  of  a  tube,  in  which  is  placed  a  small  cylinder  of  clean 


AIR  THERMOMETER.  153 

mercury.  As  the  bulb  changes  in  temperature,  the  air  with- 
in expands  and  contracts,  and  has  its  changes  of  bulb  indi- 
cated by  the  motion  of  the  metal. 

298.  The  great  expansion  of  air  by  small  increments  of 
heat,  makes  these  instruments  very  delicate,  but  they  are  li- 
able to  actions  and  accidents  which  render  them  quite  unfit 
to  replace  mercury  and  alcohol  thermometers.     In  the  first 
place,  the  bulk  of  the  air  is  readily  affected  by  pressure,  so 
that  alterations  in  the  barometer  cause  movements  in  the 
mercury  without  alteration  of  temperature.     For  the  same 
reason  difference  of  position  causes  different  indications  as 
the  cylinder  of  metal  presses  upon,  or  draws  against  the  air 
within  ;  causing  consequent  changes  of  volume.     In  the  next 
place,  the  mercury  is  liable  to  change  its  situation,  and  to 
allow  air  to  pass,  if  the  tube  be  large ;  and,  on  the  contrary, 
if  the  tube  be  small,  the  mercury  has  a  tendency  to  adhere, 
and  will  not  readily  give  way  before  the  air  pressing  on  one 
or  the  other  side  of  it. 

299.  When  another  liquid  is  used,  the  instrument    not 
only    remains    liable   to  the  effects   of  pressure,   but    is 
subject    to  other  inconveniences ;  for  if  the  fluid  be   wa- 
ter, or  an  evaporable  substance,  it  sends  a  variable  portion 
of  vapour  into  the  globe,  according  to  its  temperature,  and 
thus  occasions  expansion  not  due  to  the  mere  expansion  for 
temperature  of  the  air  within ;  if  it  be  sulphuric  acid,  it 
gradually  attracts  water,  and,  becoming  diluted,  is  then  lia- 
ble to  the  same  objection  ;  and  if  oil  be  used,  it,  together 
with  the  other  fluids,  flows  within  the  glass  tube,  adheres  to 
it,  and  does  not  leave  it  as  the  mercury  does  ;  such  adhesion 
is  incompatible  with  accurate  measurement. 

300.  These  instruments  can  only  be  used  in  connexion 
with  the  barometer.     They  merely  give  comparative  results, 
unless  indeed  their  scales  be  laid  down  at  the  time  from  a 
mercurial  thermometer;  and  then,  from  the  largeness  of  the 
degrees,  they  serve  to  indicate  very  minute  changes.     When 
mercury  is  the  substance  in  the  tube,  which,  by  its  motion, 
indicates  the  change  of  bulk  and  consequent  alteration  of 
temperature,  a  few  taps  given  to  the  instrument  will  facili- 
tate its  change  of  place.     The  instrument  should  always  be 


154  THERMOMETER— OF  AIR DIFFERENTIAL. 

used  in  the  same  position,  and  if  the  experiment  admits  of 
a  horizontal  one,  it  is  an  advantage,  for  then  the  results  are 
not  complicated  by  the  pressure  of  the  metal. 

301.  The  air  thermometer  has  had  numerous  forms  given 
to  it,  but  it  will  be  unnecessary  to  consider  all  of  them. 

-\  Sometimes  it  is  placed  with  the  bulb  upwards,  and 
the  lower  end  immersed  in  a  fluid,  which,  rising 
and  falling  within,  indicates  the  change  in  the 
volume  of  the  air :  some  objections  are  thus  avoid- 
ed, others  are  originated.  Sometimes,  in  place  of 
dipping  into  a  fluid,  the  end  is  turned  up,  and  ter- 
€p  minated  in  a  bulb  open  to  the  air,  and  this  being 
^  partly  filled  with  fluid,  a  portion  of  it  rises  into  the 
tube,  and  indicates  changes  in  the  inclosed  air  as  before. 
The  scales  attached  to  these  instruments  are  usually  of  a 
temporary  and  arbitrary  nature  ;  for  as,  from  various  causes, 
the  latter  differ  at  different  times,  they  will  not  admit  the 
application  of  permanent  portions  of  the  scales  of  other 
thermometers. 

302.  The  instrument  used  by  Mr  Leslie  in  his  investiga- 
tions differed  in  construction  from  those  described,  and  was 
by  him  named  the  differential  thermometer.     In  this  instru- 
ment, the  aperture,  instead  of  being  left  open,  is  attached  to 
a  second  ball,  similar  to  the  first,  the  tube  connecting  them 
being  bent  twice  at  right  angles,  and  the  whole  closed,  so 
that  the  indicating  fluid  within  is  entirely  free  from  the 
pressure  of  the  external  atmosphere.     The  fluid  used   is 
sulphuric  acid,  tinged  by  a  little  carmine ;  it  yields  no  va- 
pour to  the  air  in  the  bulb,  and  should  be  in  quantity  suffi- 
cient to  fill  one  of  the  perpendicular  legs  and  the  horizontal 
part  of  the  tube.     When  in  use,  the  situation  of  the  fluid  is 
observed  whilst  both  balls  are  of  equal  temperature,  and 
then  one  is  subject  to  the  heating  or  cooling  influence, 
whilst  the  other  is  retained  unchanged ;  the  motion  of  the 
fluid  in  the  tube  indicates  whether  heat  or  cold  has  been 
occasioned,  and,  comparatively,  to  what  extent*.     The  scale 
is  generally  arbitrary,  but  may  at  any  time  be  compared  ex- 
perimentally with  that  of  a  good  thermometer. 

*  Leslie's  Experimental  Inquiry  into  the  nature  and  propagation  of  Heat,  p.  9. 


IGNITION PYROMETER.  155 

303.  With  respect  to  instruments  fitted  to  measure  higher 
degrees  of  heat  than  those  which  can  be  borne  by  mercuri- 
al thermometers,  we  are  yet  deficient ;  nor  does  it  seem 
likely  that  the  want  will   soon  be  supplied.     The  student 
will  do  well  to  observe  the  appearances  of  a  furnace  or  a 
substance,  as  it  rises  from   a  dull   red  heat  to  the  highest 
possible  temperature  that  can  be  given  to  it ;  to  form  in  his 
mind  a  clear  idea  of  the  colour  and  appearance  of  the  light 
emitted  in  succession  ;  and  to   select  three  or  four  distinct 
periods  of  the  ignition  to  serve  him,  as  it  were,  for  degrees. 
The  terms  dull  red,  red,  full  red,  yellow,  white,  bluish  white, 
or  any  others  he  may  choose,  should  not  be  quite  indefinite, 
but  so  far  understood  and  appreciated,  and  the  appearance 
he  intends  to  express  by  them  so  fixed  in  his  mind,  that  he 
may  be  able  to  say  at  once  whether  a  fire  is  above  or  below 
any  required  degree  ;  or,  having  registered  a  particular  heat 
by  its  appearance  in  his  note  book,  that  he  may  be  able  to 
attain  it  again  with  considerable  accuracy. 

304.  The  instrument  called  Wedgwood's  pyrometer,  at 
one  time  claimed  much  attention,  for  the  apparent  facility 
of  its  application,  and  accuracy  of  its  results.     It  consisted 
of  pieces  of  clay  which,  being  heated  to  a  higher  or  lower 
degree,  contracted  more  or  less;  and  the  contraction  being 
measured,  was  considered  as  proportionate  to,  and  therefore 
a  measure  of,  the  temperature  to  which  they  had  been  sub- 
jected.    Sir  James  Hall,  however,  showed  that  the  indica- 
tions were  fallacious,  inasmuch  as  the  same  contraction  was 
produced  by  a  long  low  heat  as  by  a  shorter  and  higher  one. 
Even  supposing  this  could  to  a  certain  degree  be  guarded 
against  by  attention  to  time,  the  instrument  is  inapplicable, 
because  the  pieces  of  clay  are  no  longer  prepared  and  sold, 
in  consequence,  as  it  is  understood,  of  irregularities  in  the 
kinds  obtained  from  different  sources. 

305.  Daniell's  pyrometer,  the  best  instrument  of  the  kind* 
which  has  been  constructed,  claims  our  attention.     Its  indi- 
cations result  from  a  difference  in  the  expansion  and  con- 
traction of  a  platinum  bar,  and  a  tube  of  black  lead  ware  in 

*  Quarterly  Journal  of  Science.,  xi.  309. 


156  COMMINUTION. 

which  it  is  contained.  These  differences  are  made  available 
by  connecting  an  index  with  the  platinum  bar,  which  traverses 
a  circular  scale  fixed  on  to  the  tube.  The  degrees  marked  on 
the  scale,  though  arbitrary,  are  in  each  instrument  compared 
experimentally  with  those  of  the  mercurial  scale,  and  the 
ratio  marked  on  the  instrument;  so  that  its  degrees  are  rea- 
dily convertible  into  those  of  Fahrenheit.  The  instrument, 
after  use,  will  return  on  cooling  to  the  point  from  which  it 
set  out,  and  when  applied  to  ascertain  a  particular  tempera- 
ture, the  fusing  point  of  silver,  for  instance,  will  give  nearly 
the  same  indication  every  time.  It  is,  therefore,  much  su- 
perior to  any  other  that  has  yet  been  constructed  to  measure 
high  temperatures.  More  recently,  Mr  Daniell  has  improv- 
ed this  instrument  still  farther  by  separating  the  scale  from 
the  indicating  part,  so  that  the  latter  may  be  placed  wholly 
in  the  fire,  or  even  immersed  in  fused  metal.  Hence,  although 
not  so  facile  in  its  use  as  the  common  thermometer,  which, 
indeed,  is  remarkable  for  its  simplicity,  yet  it  promises  to  be 
of  extensive  use;  and  in  the  numerous  situations  where  cir- 
cumstances admit  of  its  application,  as  in  glass-houses,  pot- 
teries, furnaces  of  all  kinds,  &c.,  it  far  surpasses  any  other 
instrument,  and  furnishes  indications  of  great  comparative 
delicacy. 


SECTION  V. 

COMMINUTION. 

Trituration,  Mortars,  Granulation,  Precipitation. 

306.  THE  division  of  matter  is  often  highly  advantageous 
in  facilitating  chemical  action,  and  various  processes  have 
been  devised  for  effecting  it  in  the  laboratory ;  some  suited 
to  the  nature  of  the  substance  to  be  divided,  others  to  the 
particular  state  of  division  required.  These  processes  are 
both  mechanical  and  chemical ;  for  fusion  and  solution  are 


TRITURATION — MORTARS.  157 

more  frequently  referred  to  as  means  of  separating  the  par- 
ticles of  matter  one  from  another,  than  for  any  other  purpose 
(356).  The  latter  processes  will  not  be  dwelt  upon  at  pre- 
sent ;  what  relates  to  them,  connected  with  the  object  of  this 
book,  may  be  arranged  more  conveniently  in  other  sections, 
and  hence,  in  this,  the  references  to  them  will  be  only  inci- 
dental. The  operations  more  immediately  in  view  are  those 
which,  while  they  divide  a  substance,  do  not  alter  its  physi- 
cal state.  These  of  course  apply  to  solid  bodies  only,  and 
the  substance,  after  the  operation,  is  still  in  the  solid  form, 
however  minutely  the  particles  may  have  been  divided.  No 
merely  mechanical  division  can  bring  a  solid  body  into  a 
state,  comparable  as  to  physical  properties,  with  the  same 
body  when  it  has  had  freedom  of  motion  given  to  its  parti- 
cles by  fusion  or  solution. 

307.  Of  all  the  processes   adopted  in  the  laboratory  for 
these  purposes,  none  is  more  extensively  useful  than  that  of 
trituration  ;  chemical  operations  cannot  proceed  well  with- 
out it ;  nor  is  any  vessel  more  generally  convenient  for  the 
purpose  than  the  mortar  and  pestle,  and  hence,  to  meet  the 
quantities  and  qualities  of  different  substances,  several  of 
these  vessels,  of  various  sizes  and  materials,  should  be  in- 
cluded in  the  laboratory  apparatus. 

308.  In  the  first  place,  a  large  iron  mortar,  with  its  pes- 
tle of  the  same  material,  and  of  a  proper  size  and  weight, 
should  stand  on  a  block  in  some  corner  or  convenient  place 
in  the  laboratory  (19).     It  is  useful  for  breaking  large  lumps 
into  smaller,  and  for  the  pulverization  of  ores,  metals,  and 
heavy,  coarse  materials.     Two  or  three  mortars  formed  of 
earthy  materials,  and  of  moderate  sizes,  from  a  pint  to  three 
pints  in  capacity,  should  be  provided  for  table  use,  and  a 
smaller  one  for  rare  substances.     Those  which  are  intended 
to  effect  the  pulverization,  and  at  times  the  solution  of  vari- 
ous bodies,  ought  to  possess  requisites  which   it  is  difficult 
to  find  combined.     A  vessel  is  required  of  a  material  so 
hard  as  to  bear  the  blows  and  friction  of  other  hard  bodies 
for  any  length  of  time,  without  suffering  injury  or  abrasion 
of  its  surface ;  of  an  uniform  and  compact  texture ;  not 
brittle  ;  not  permitting  the  absorption  of  fluids,  or  penetra- 


158  MORTAR — PESTLE. 

tion  by  them ;  not  subject  to  the  action  of  acids,  alkalies,  or 
solutions ;  and  of  a  requisite  capacity. 

309.  The  difficulty  of  finding  these  properties  united, 
has  caused  the  introduction  of  a  variety  of  mortars  for  vari- 
ous uses.     Those  for  common  occasions  should  admit  of  the 
pulverization  of  most  substances,  and  the  preparation  of 
acid,  alkaline,  and  metallic  solutions.     These  purposes  were 
well  answered  formerly  by  mortars  of  Wedgwood's  ware, 
and  there  were  some  excellent  ones  to  be  bought  with  the 
name  of  Mist  upon  them  ;  but  at  present  no  mortars  made 
of  porcelain  or  artificial  ware  can  be  procured   fit  for  the 
laboratory.     Both  form  and  material  have  deteriorated*. 
A  mortar  of  this  kind  should  scarcely  allow  of  being  scratch- 
ed by  the  edge  of  a  piece  of  quartz  or  flint,  and  absolutely 
resist  steel,  not  by  any  glaze  on  its  surface,  but  on  an  acci- 
dental fracture,  as  well  as  other  parts.     It  should  not  be 
stained  by  having  a  strong  acid  solution  of  sulphate  of  cop- 
per or  muriate  of  iron  put  into  it  when  dry,  and  left  for 
twenty-four  hours,  but  should  allow  the  salt  to  be  washed 
off  without  any  difficulty  by  cold  water.     On  rubbing  down 
an  ounce  of  sharp  river  or  sea  sand  to  fine  powder,  the 
sand  should  acquire  no  appreciable  increase  of  weight.     It 
should  be  sufficiently  thick  at  the  bottom  to  resist  the  blows 
to  which  it  will  at  times  be  subject,  as  well  as  to  give  weight 

and  steadiness.  It  should  not  be  of  brittle 
material,  and  therefore  fragile  or  apt  to  shiv- 
er, though,  if  unavoidable,  that  fault  is  more 
easily  borne  with  than  any  other  of  those 
mentioned.  The  proportionate  thickness  of 

the  vessel  in  different  parts  relative  to  its  capacity  may  be 

represented  by  the  accompanying  woodcut. 

310.  The  pestles  should  be  of  one  piece,  and  of  the  same 
material  and  qualities  as  the  mortar.     If  in  two  pieces,  as  is 
sometimes  the  case,  the  handle  being  of  wood  and  the  bot- 
tom only  of  ware,  the  cement  by  which  they  are  fastened 
occasionally  falls  out,  and  produces  injury  to  the  materials 
in  the  mortar  ;  or  by  the  contraction  of  the  wood,  and  other 

*  Messrs  Wedgwood  are  occupied  in  endeavouring  to  improve  this  manufacture 


FORM DIMENSIONS.  159 

causes,  a  space  is  formed,  which,  sometimes  receiving  and 
sometimes  delivering  dirt,  may  injure  an  experiment.  The 
pestle  should  be  strong,  and  its  size  such  as  may  be  suffi- 
cient above  to  allow  of  its  being  grasped  firmly  in  the  hand 
and  below  to  permit  a  considerable  grinding  surface  to  come 
in  contact  with  the  mortar.  Its  diameter,  in  the  lower  part, 
may  be  about  one-third,  or  one-fourth  of  the  upper  diameter 
of  the  mortar.  The  curve  at  the  bottom  should  be  of  short- 
er radius  than  the  curve  of  the  mortar,  that  it  may  not 
touch  the  mortar  in  more  than  one  part,  whilst  at 
the  same  time  the  interval  around  may  gradually 
increase,  though  not  too  rapidly  towards  the  up- 
per part  of  the  pestle.  A  mortar  and  pestle  of 
the  relative  convexity  figured  in  the  margin,  may, 
by  inclining  the  pestle,  or  bringing  it  to  different  parts  of 
the  mortar,  allow  portions  of  such  different  curvature  to  be 
placed  in  juxtaposition,  that  the  intervening  space  shall  in- 
crease more  or  less  rapidly  from  the  point  of  contact,  in  al- 
most any  proportion  ;  a  variation  which  it  is  of  considerable 
consequence  in  pulverization  to  obtain  with  facility. 

311.  Neither  pestle  nor  mortar  should  be  quite  smooth  at 
the  grinding  surfaces,  or  the  materials  will  slip  about  be- 
tween them,  and  not  be  retained   and   pulverized.      The 
roughness  of  unglazed  ware  is  quite  sufficient  for  this  purpose. 
A  roughness  of  this  kind  is  sometimes  obtained  by  use,  and 
is  the  best  that  can  be  produced;  but  it  indicates  that  the 
mortar  is  abraded  by  the  substances  rubbed  in  it,  and,  if  it 
happens  quickly,  shows  that  the  vessel  is  deficient  in  hard- 
ness.    When  the  mortar  is  such  as  to  wear  but  little,  and  is 
good  in  other  respects,  it  is  then  proper  to  rub  a  quantity  of 
sharp  sand  or  emery  to  powder  in   it,  until    the  required 
roughness  of  surface  is  produced.     The  operation  will  be 
long  and  laborious,  but  a  good  mortar  will  repay  the  pains  it 
requires.     Besides  these  mortars,  a  couple  of  small  ones  of 
the  same  materials  should  be  procured.     They  should  all  of 
them  be  lipped,  for  the  convenience  of  pouring  out  fluids  or 
fine  powders. 

312.  Excellent  porphyry  mortars  are  brought  to  this  coun- 
try from  Sweden  ;  they  are  very  hard,  and  resist  all  ordinary 


160  MORTARS AGATE OTHER  KINDS. 

chemical  action,  but  they  cannot  be  obtained  of  large  size, 
and  are  expensive,  from  the  difficulty  of  making  them  out  of 
a  solid  block.  Their  forms  are  variable,  being  in  part  de- 
pendent upon  the  pieces  out  of  which  they  are  worked. 
They  should  be  accompanied  with  pestles  of  the  same  sub- 
stance. 

313.  Small  mortars  and  pestles  are  also  made  of  agate, 
and  are  exceedingly  useful  for  the  pulverization  and  mixture 
of  small  portions  of  matter,  which  have  either  been  weighed 
or  are  scarce.     They  are  generally  made  more  shallow  than 
ordinary  mortars,  arid,  in  consequence  of  their  form,  size, 
hardness,  and  closeness  of  surface,  allow  of  the  matter  being 
collected  with  less  risk  of  loss  than  from  mortars  of  earthen- 
ware.    Their  hardness  is  such  as  to  enable  them  to  resist 
abrasion  better  than  any  others.     They  should  not  be  incon- 
siderately subjected  to  blows,  being  more  brittle  than  the 
porphyry  or  ware  mortars,  and  occasionally  having  numerous 
and  almost   imperceptible  cracks  running   through   them, 
which,  though  so  close  as  not  to  interfere  with  their  ordinary 
use,  render  them  weak.     If  agate  mortars  be  not  left  rough- 
ened within  by  the  workman,  it  takes  a  long  time  by  ordi- 
nary wear  to  render  them  so.     It  is  better,  therefore,  to  effect 
it  in  such  cases  by  means  of  the  pestle,  and  a  little  emery  or 
sharp  sand. 

314.  Mortars  of  wood,  marble,  or  iron,  are  unfit  for  ordi- 
nary laboratory  service,  because  of  their  softness,  and  the 
action  of  different  fluids   and  substances  upon  them.     A 
wrought-iron  mortar  of  from  a  pint  to  a  quart  in  capacity  is 
useful  in  particular  cases,  not  merely  for  the  pulverization  of 
substances  which,  not  acting  upon  it,  would  be  too  tough  or 
require  too  many  blows  for  a  common  mortar,  but  also  as  a 
vessel  to  contain  mercury  in  its  ordinary  or  in  a  heated  state; 
it  should  have  an  accompanying  pestle  of  iron.     Glass  mor- 
tars are  generally  unfit  for  the  laboratory,  being  too  soft 
and  brittle,  and  yielding  both  alkali  and  lead  to  particular 
solvents.     Their  uses  are  indeed  so  confined  as  to  render  it 
wise  to  exclude  them  altogether. 

315.  Let  us  now  consider  the  operations  in  which  a  mor- 
tar is  available.     Most  stones  may  be  broken  if  held  lightly 


BREAKING   TO  PIECES FRAGMENTS   CONFINED.  161 

in  the  left  hand  and  struck  smartly  with  a  hammer  ;  but  when 
the  pieces  are  reduced  beneath  a  certain  size,  their  inertia 
does  not  then  afford  sufficient  resistance.  In  these  and  in 
other  cases,  the  substance,  if  not  too  hard,  may  be  broken 
into  smaller  pieces  very  conveniently  in  a  mortar,  without 
loss  ordispersion  of  the  fragments.  For  this  purpose  it  should 
be  placed  in  the  mortar,  and  struck  with  the  pestle  in  suc- 
cessive sharp  firm  blows,  but  not  too  forcibly.  If  the  body 
be  rather  tough,  as  a  piece  of  sal  ammoniac,  the  pestle  should 
be  held  firmly  in  the  hand,  and  impelled,  not  merely  by  its 
descending  weight,  but  the  force  of  the  arm  should  be  added 
and  continued,  until  it  is  stopped  by  the  substance,  some- 
thing like  a  thrust  being  given  to  it  as  well  as  a  blow.  On 
the  contrary,  if  the  substance  be  brittle,  as  glass,  or  many 
ores,  it  is  better  to  hold  the  pestle  lightly  in  the  hand,  and, 
having  urged  it  downwards,  to  let  it  fall  upon  the  substance 
with  little  more  than  its  own  force,  using  it  rather  as  the  head 
of  a  hammer,  than  in  the  former  manner. 

If  there  be  any  risk  of  the  fragments  being  thrown  about, 
the  mortar  should  be  covered  with  a  flat  piece  of  pasteboard 
or  millboard,  having  a  hole  in  the  middle,  through  which 
the  pestle  may  be  passed.  The  fragments  broken  from  the 
piece  pass  from  under  the  pestle,  and  have  a  general  ten- 
dency up  the  sides  of  the  mortar;  hence  a  cover  of  this  kind 
is  quite  sufficient  to  oppose  their  passage,  and  retain  them 
within  the  vessel,  notwithstanding  the  hole  in  the  centre 
should  be  considerably  too  large  to  be  filled  by  the  pestle. 
For  this  reason  one  such  cover,  in  a  clean  state,  will  suffice 
for  mortars  of  different  sizes,  and  should  have  its  assigned 
place  on  the  walls  of  the  laboratory.  When  such  a  cover  is 
not  at  hand,  a  clean  cloth  with  a  hole  in  it  for  the  passage 
of  the  pestle  may  be  used,  being  drawn  by  one  hand  tightly 
over  the  mouth  of  the  mortar,  whilst  the  other  holds  the  pes- 
tle. This  is  better  than  to  cover  both  mortar  and  pestle  with 
a  whole  cloth,  and  to  grasp  the  pestle  through  it,  whilst 
breaking  the  body ;  for  then  the  cloth  hangs  in  folds,  is  con- 
siderably agitated,  and  frequently  catches,  and  even  scatters 
portions  of  the  substance. 

316.  If  the  piece  to  be  broken  be  too  hard  for  the  mortar, 
V 


162  BREAKING  ON  THE  ANVIL. 

whilst  large,  which  is  now  and  then  the  case,  or  there  be 
reason  to  fear  injury  from  it,  then  it  must  be  either  broken 
in  the  hand  (315),  or  split  or  crushed  by  a  hammer  on  the 
anvil.  When  of  convenient  size,  it  should,  after  being  laid 
upon  the  anvil,  be  surrounded  by  the  hand,  or  by  the  thumb 
and  one,  two,  or  three  fingers,  according  to  its  size,  so  that, 
when  struck  by  the  hammer,  and  split  into  several  pieces, 
these  should  not  be  scattered,  but  retained  together,  and  af- 
terwards separated  by  the  fingers.  The  blows  should  be 
steady,  small  at  first,  and  increased  in  force,  until  sufficiently 
powerful.  It  is  not  desirable  to  crush  the  substance  at  once, 
but  to  break  it  into  large,  and  afterwards  into  smaller  frag- 
ments ;  and  if  the  body  be  one  which  gives  way  by  degrees, 
the  fracture  should  be  effected  by  successive  blows,  and  not 
on  a  sudden.  It  is  desirable  that  the  chemist  should,  in 
everything  he  does,  endeavour  to  obtain  a  command  over  the 
agents  he  is  using,  and  not  apply  them  with  such  force,  or  so 
carelessly,  as  to  render  the  results  accidental.  Even  in  the 
breaking  of  a  stone,  advantage  is  gained  by  a  cautious  mode 
of  procedure,  not  merely  as  confirming  a  good  habit,  but  as 
most  effectually  preventing  waste,  and  sometimes  in  preserv- 
ing peculiar  internal  appearances. 

317.  When  the  substance  requires  a  blow  so  hard,  that  it 
is  unpleasant  to  expose  the  hand  or  fingers  to  the  effects 
which  may  happen  upon  its  fracture,  it  may  be  wrapped  up 
in  one  or  several  folds  of  strong  paper  or  cloth,  and  then 
be  struck.     If  the  blow  break  it,  the  result  will  be  indicated 
by  the  sound,  and  the  feel  of  the  hammer  in  the  hand;  if  it 
does  not,  but  at  the  same  time  cuts  the  paper  or  cloth  through, 
it  is  not  necessary  for  that  reason  to  change  the  envelope, 
but  the  blow  must  be  repeated  upon  the  same  place,  until 
the  body  does  separate.     In  both  cases  the  fragments  will  be 
held  together  by  the  envelope,  and  it  is  easy  to  separate 
them  from  the  wrapper  when  opened  out,  by  a  little  motion 
and  friction. 

318.  Some  substances,  and  especially  some  of  the  metals, 
as  cast  iron,  copper,  alloys  of  copper,  &c.,  when  in  mass  and 
cold,  can  scarcely  be  broken  into  smaller  pieces  on  the  anvil, 
except  by  blows  so  powerful  as  to  endanger  neighbouring 


THE   GRAIN BREAKING   SMALL,  163 

bodies,  and  yet  will  crack  and  crumble  with  facility  when 
heated.  In  these  cases,  the  substances  should  be  made  red 
hot,  and  struck  in  that  state,  until  they  are  sufficiently  cracked, 
and  the  separation  completed  in  the  vice,  either  immediately; 
or  after  the  temperature  has  fallen. 

319.  Before  leaving  this  subject  of  the  division  of  large 
pieces  into  smaller,  it  will  be  proper  to  observe  that  many 
substances  may  be  separated  by  nippers  or  a  knife.     In  these 
cases  it  is  necessary  to  attend  to  the  grain  of  the  substance, 
and  take  advantage  of  the  greater  facility  of  division  which 
exists  in  one  direction  than  in  another.     Muriate  of  ammo- 
nia will  separate  readily  with  the  grain  into  pieces  without 
much  crumbling.     If  it  is  to  be  pulverized,  place  it  in  the 
mortar  with  the  grain  upright,  and  not  horizontal. 

320.  It  may  be  remarked  that  there  are  many  substances, 
which,  though  too  hard  to  be  broken  in  the  mortar  when  in 
large  masses,  without  endangering  its  fracture,  or  the  abra- 
sion of  its  surface,  still  may  be  readily  and  properly  pulver- 
ized when  in  smaller  pieces. 

321.  If  the  object  be  to  reduce  the  substance  into  minute 
fragments  only,  of  the  size  of  a  pea,  or  pin's  head,  or  smaller, 
but  not  to  powder ;  then,  having  broken  it  down  as  before 
described,  the  operation  is  to  be  continued  in  the  mortar,  by 
a  series  of  blows  from  the  pestle,  all  grinding  action  being 
avoided.     The  pestle  must  be  held  lightly,  and  allowed  to 
fall  sharply  on  the  substance,  being  directed  to  those  places 
where  the  largest  pieces  are.     A  slight,  lateral,  or  shaking 
motion  of  the  hand  holding  the  mortar,  between  each  blow, 
will  help  to  return  the  larger  pieces  from  the  edge  towards 
the  middle  of  the  mass  of  fragments,  where  they  ought  to  be 
when  struck,  and  no  blow  should  be  given  towards  the  edge, 
if  it  can  be  avoided  ;  it  there  only  tends  to  reduce  those  par- 
ticles smaller  which  are  small  enough,  and  if  a  large  piece 
be  struck  there,  its  fragments  are  apt  to  fly  up  the  sides  of 
the  mortar  ;  whereas,  if  it  were  in  the  middle  of  the  substance, 
they  are  caught  and  retained  by  the  surrounding  matter. 

322.  It  will  be  found  that  a  process  of  this  kind,  in  which 
all  grinding  action  is  avoided,  will  reduce  a  substance  to 
small  fragments  or  particles,  with  the  least  production  of 


1C4  PULVERIZATION. 

fine  powder  ;  and  this  is  highly  desirable  with  some  sub- 
stances which  are  in  a  more  favourable  state  for  experiment, 
when  crushed  or  broken  into  small  pieces  only,  than  when 
more  minutely  reduced.  Flint  glass  is  as  convenient  a  sub- 
stance as  any  for  the  student  to  practise  upon  for  the  ac- 
quirement of  these  methods  and  illustration  of  their  effects. 

323.  In  pulverization  a  very  different  action  of  the  pestle 
and  hand  is  required.     The  object  then  is  to  reduce  the 
whole  of  the  substance  into  fine  particles  as  rapidly  as  pos- 
sible.    The  process  of  striking  or  stamping  would  now  be 
found  too  slow  ;  a  grinding  action  is  necessary  to  expedite 
the  operation,  and  this  it  will  be  proper  to  adopt  as  soon  as 
possible.     Even,  therefore,  whilst  breaking  down  the  larger 
lumps  into  smaller,  it  will  be  desirable  to  alter  the  character 
of  the  blow  ;  and  instead  of  holding  the  pestle  lightly  in 
the  hand,  and  letting  it  almost  drop  on  to  the  middle  of  the 
substance,  it  should  be  grasped  firmly,  and  forced  down  by 
the  muscles  of  the  wrist  and  arm,  pressure  being  added  to 
the  blow  ;  and  it  should  be  made  to  fall  on  the  substance  at 
the  side  of  the  mortar,  the  pressure  being  continued  till  the 
pestle  has  reached  the  middle.     The  blow  is  to  be  oblique 
in  its  direction,  going  down  the  side  of  the  mortar  to  the 
centre.     It  is  best  given  on  the  part  farthest  from  the  ope- 
rator, more  force  being  then  exerted,  as  it  is  continued  by  a 
downward  pressure  to  the  middle  of  the  mortar.     This  kind 
of  stroke  breaks  the  larger  fragments,  grinds  both  these  and 
the  smaller,  and  mixes  and  alters  the  position  of  the  whole; 
and,  if  continued  in  the  same  direction  whilst  the  mortar  is 
turned  a  little  way  round  by  the  other  hand  between  each 
stroke,  every  part  of  Ihe  substance  is  brought  in  succession 
under  its  comminuting  action. 

324.  The  substance  is  thus  soon  reduced  to  particles  so 
small,  that  the  pressure  of  the  hand  is  sufficient  to  continue 
the  division  without  the  force  of  a  blow.     After  this  it  is 
most  expeditious  to  advance  the  operation  by  rubbing.     For 
this  purpose,   the   pestle,  being  grasped   firmly,  should  be 
moved  in  larger  or  smaller  circles  around  the  centre  of  the 
bottom,  at  the  same  time  pressing  hard  and  regularly  upon 
it.     It  is  in  vain  to  expect  a  rapid  effect  in  this  operation 


PULVERIZING  IN  MORTARS.  165 

without  pressure,  or  to  give  pressure  without  labour,  but 
certainly  much  labour  is  exerted  in  vain  by  those  who  give 
an  unequal  and  uncertain  pressure.  The  motion  of  the 
pestle  should  be  in  circles,  commencing  at  the  centre,  and 
gradually  expanding  outwards :  this,  whilst  it  grinds  the 
substance,  gradually  displaces  it,  turns  it  over,  and  mixes  it. 
When  it  has  arrived  at  the  exterior  of  the  mass,  the  circles 
described  should  gradually  be  contracted,  until  they  have 
again  closed  in  the  middle,  when  they  should  re-expand, 
and  thus  the  operation  be  continued  until  the  powder  be 
sufficiently  fine.  The  process  is  least  fatiguing  to  the 
hand  when  the  circles  are  up  the  side  of  the  mortar,  to- 
wards the  limits  of  the  substance,  and  the  grinding  proceeds 
most  rapidly  there.  By  making  a  smaller  circle  now  and 
then,  it  is  easy  to  urge  the  fragments  outwards  in  that  di- 
rection, so  as  to  take  advantage  of  the  most  favourable  cir- 
cumstances. Occasionally,  deviations  from  this  regularity 
may  be  convenient,  for  the  purpose  of  moving  the  substance 
in  different  directions;  but  it  will  be  found  that  the  more 
nearly  they  are  adhered  to,  the  more  rapid  will  be  the  ope- 
ration. 

325.  The  pestle  may  be  held  in  both  hands  in  succession, 
for  the  relief  of  the  wrists;  but  the  hand  not  occupied  by  it 
should  take  charge  of  the  mortar,  and,  holding  it  firmly  and 
steadily,  should  sometimes  turn  it  a  little  way  round,  espe- 
cially if  the  force  of  the  hand  holding  the  pestle  be  unequal 
in  different  parts  of  the  circle.     The  motion  of  the  pestle 
may  be  either  in  one  direction  or  the  other,  and  an  inversion 
of  it  is  now  and  then  advantageous  for  the  more  effectual 
mixture  of  the  particles.     During  the  whole  process  it  should 
be  observed,  that  every  part  of  the  powder  is  rubbed,  and 
the  tendency  should  be  to  grind  those  parts  first  which  ap- 
pear coarsest,  and  not  to  finish  one  portion  before  another. 

326.  The  opportunity  already  referred  to  of  obtaining 
different  inclinations  between  the  surface  of  the  pestle  and 
that  of  the  mortar  (310),  by  either  inclining  the  pestle  or 
carrying  it  to  different  parts  of  the  mortar,  may  now  be 
taken  advantage  of.     At  the  commencement  of  the  grind- 
ing, for  instance,  whilst  the  particles  are  coarse,  it  will  be 


166         USES  OF  THE  PARTS  OF  THE  MORTAR. 

proper  to  incline  the  pestle  so,  that  the  preceding  part  may 
pass  over  them ;  by  which  they  are  included  between  it  and 
the  mortar,  and  are  crushed  by  the  following  part.  Particles 
are  thus  instantly  broken  down,  which,  if  the  pestle  were 
held  upright,  or  if  inclined  in  a  wrong  direction,  would 
merely  be  pushed  forward.  In  the  same  way,  even  when 
the  powder  is  of  considerable  fineness,  the  pestle  may  be 
made  to  have  more  of  a  mixing  or  a  grinding  effect,  accor- 
ding as  it  is  inclined  one  way  or  the  other — both  being  pe- 
culiarly desirable  at  times.  Many  other  advantages  of  this 
kind  are  attainable,  which  are,  however,  better  learnt  by 
practice  than  from  description,  which  would  necessarily  be 
very  minute  and  tedious,  and  at  the  same  time  very  imper- 
fect. 

327.  The  student  should  be  aware  also  of  the  peculiar 
uses  of  the  different  parts  of  the  inner  surface  of  the  mortar. 
The  powder  lies  quietly  at  the  bottom  of  the  mortar ;  on  the 
sides,  a  little  way  from  the  centre,  it  also  rests  with  facility, 
but  with  a  tendency  to  pass  to  the  middle  as  the  pestle 
moves  over  it ;  farther  outwards  it  arrives  at  a  part  so  in- 
clined, that,   when  forced  upwards  as  the  pestle  passes,  it 
falls  back  again  when  left  at  liberty  ;  here  consequently  a 
mixing    agency   may   be  exerted,   whilst  the  operation  of 
grinding  goes  on  more  effectually  at  a  part  nearer  the  cen- 
tre, not  merely  because  the  powder  rests  there  and  awaits 
the  approach  of  the  pestle,  but  also  because,  from  its  being 
nearer  to  a  horizontal  position,  the  hand  has  more  command 
over  the  pestle,  and  power  in  pressing  it  down. 

328.  The  quantity  of  a  substance  put  into  the  mortar  at 
once,  should  bear  a  proportion  to  its  particular  qualities  and 
to  the  ultimate  state  of  fineness  required.     If  the  substance 
is  to  be  finely  pulverized,  only  small  quantities  should  be 
operated  on  at  once,  so  as  to  form  but  a  thin  layer  at  the 
bottom  in  those  places  which  the  pestle  has  passed,  and  to 
insure  the  subjection  of  the  whole  to  trituration.     If  the  lay- 
er under  the  pestle  be  thick,  a  grain  may  be  imbedded  in  it, 
and  remain  uncrushed  by  the  pressure.     If  the  substance  be 
in  great  quantity,  a  particle  may  be  pushed  about  from  side 
to  side,  enveloped  in  the  mass,  and  without  coming  under 


QUANTITY ITS  EFFECT  AND  MANAGEMENT.       167 

the  pestle  at  all ;  and  what  may  happen  to  one  particle  may 
happen  to  many,  and  thus  the  powder  be  a  mixture  of  coarse 
and  fine.  For  coarse  powders  larger  quantities  may  be 
taken.  Hence,  also,  when  a  lump  is  to  be  broken  down  in- 
to a  fine  powder,  it  is  frequently  better  to  reduce  it  to  a 
coarse  powder,  and  then,  removing  it  from  the  mortar,  to 
return  it  in  small  portions,  each  of  which  is  to  be  brought 
to  the  state  of  fine  powder  by  itself. 

329.  A  soft  or  readily  pulverizable  body  may  be  put  into 
the  mortar  in  larger  quantities  than  a  hard  one ;  thus  a 
larger  quantity  of  chalk  may  easily  be  reduced  to  a  fine 
powder  at  once,  whereas,  if  as  much  siliceous  sand  were 
operated  upon,  the  attempts  to  reduce  it  to  a  powder  as 
fine  would  fail,  or  be  interminable.     It  is  easy  to  understand 
that  any  substance  whose  particles  are  so  hard  as  to  require 
direct  pressure  between  the  mortar  and  pestle,  is  in  too 
great  a  quantity  when  there  is  so  much  present  as  to  pre- 
vent the  approach,  almost  to  contact,  of  the  two  grinding 
surfaces. 

330.  The  state  of  fineness  to  which  a  powder  has  been 
reduced  is  judged  of  principally  by  the  appearance.     If  the 
body  be  coloured,  the  colour  becomes  paler  as  the  powder 
is  finer,  and  generally  at  last  almost  disappears.     When  the 
powder,  in  place  of  flowing  freely  down  the  sides  of  the 
mortar,  begins  to  adhere  and  clot  as  it  were,  it  is  also  a 
mark  of  considerable  division  ;   and  when  it  is  in  such  a 
state  that,  previously  dry  and  granular,  it  now  seems  almost 
moist,  and,  being  moved  about  by  a  spatula,  preserves  the 
form  given  to  it  even  when  the  lateral  surfaces  are  perpen- 
dicular, it  is  then  in  an  extreme  state  of  division.     This  in- 
dication must,  of  course,  be  considered  in  connexion  with 
the  hygrometric  powers  of  the  body. 

The  student  may  observe  all  these  appearances  by  opera- 
ting upon  a  few  fragments  of  bottle  glass  (not  flint  glass, 
for  then  some  fallacies  are  introduced),  or  a  few  pieces  of 
calcined  flint. 

331.  Passing  from  this  general  consideration  of  the  pro- 
ess  of  pulverization,  it  may  be  observed  that  particular 

bodies  require  slight  variations  in  the  process  for  particular 


J  68     PULVERIZATION FACILITIES  IN  PARTICULAR  CASES. 

purposes.  If  the  substance  be  poisonous,  or  if  it  be  in  exceed- 
ingly fine  powder,  and  liable  to  dispersion  from  the  motion  of 
the  air,  it  may  advantageously  be  moistened  with  a  little 
water,  provided  that  the  fluid  has  no  action  upon  it;  but  the 
trituration  is  then  more  laborious,  from  the  greater  difficulty 
of  mixture  and  the  adhesion  of  the  substance:  it  is,  however, 
a  precaution  continually  adopted  with  substances  subjected 
to  the  grinding-mill.  When  the  pulverization  is  finished 
the  substance  may  be  dried,  if  that  be  necessary,  or,  if  not, 
left  in  the  state  in  which  it  comes  from  the  mortar.  At  other 
times,  to  confine  the  powder,  the  mortar  may  be  closed  up 
by  a  cover,  a  mill-board,  or  a  cloth,  as  described  in  the  di- 
rections for  breaking  down  substances  (315) ;  but  the  aper- 
ture should  now  be  as  small  as  possible,  or  the  finer  particles 
will  escape  by  it. 

332.  When  the  substance  to  be  pulverized  is  stony  and 
hard,  advantage  is  frequently  gained  by  igniting  the  mass, 
and  quenching  it  in  water.     Flints,  many  siliceous  and  other 
hard  stones,  are  thus  rendered  more  brittle  and  divisible, 
and  their  comminution  considerably  facilitated.     Charcoal 
is  a  substance  which  is  found  to  pulverize  with  far  greater 
ease  and  rapidity  when  hot,  or  after  being  recently  heated, 

han  when  cold;  ignite  it,  therefore,  and  in  this  state  intro- 
duce it  into  the  mortar,  and  instantly  rub  it  to  powder.  Cam- 
phor, which  has  a  toughness  under  the  pestle,  is  easily 
reduced  to  powder  when  moistened  with  a  few  drops  of  alco- 
hol. Gum,  when  pulverized,  should  be  kept  perfectly  dry. 
Zinc  may  be  reduced  to  powder  when  hot,  in  a  heated  iron 
mortar,  the  pestle  also  being  heated.* 

333.  Shell-lac,  some  resins,  and  other  substances,  when 
divided  for  the  purpose  of  facilitating  solution,  are  better  in 
small   fragments  than  in  fine   powder.     Adhesive  organic 
substances,  which  would  knead  together  under  the  pestle, 
are  frequently  rendered  capable  of  division  in  the  mortar,  by 
being  mixed  with  clean  sand  or  glass;  such  substances  being 

*  Some  substances  liable  to  the  softening  influences  ofmoderate  heat,  such  as 
liquorice  and  opium,  may  be  reduced  to  powder  in  cold  weather,  or,  in  a  refri- 
gerated raortar. — Ed,- 


POWDERS  MOVED MEANS  USED.  169 

chosen  in  these  cases  as  will  be  inert  with  respect  to  the 
agents  to  which  the  bodies  are  to  be  subjected.* 

334.  The  transference  of  materials  to  and  from  the  mor- 
tar, and  generally  of  substances  in  powder  or  small  grains, 
is  most  conveniently  effected  by  the  use  of  spatulas,  or  simi- 
lar instruments.     Common   broad  bone  paper-knives  make 
excellent  spatulas  for  the  laboratory,  for  this  and  other  uses 
and  may  be  used  to  disturb  or  separate  the  substance  when 
it  adheres  together  in  the  mortar,  or  to  the  sides  of  the  ves- 
sel ;  but  the  precaution  must  be  taken  of  not  using  them  in 
those  cases  where  they  may  affect  or  be  affected  by  the  sub- 
stance, or  where,  from  its  strong  adhesion  to  the  mortar,  the 
removal  may  cause  such   abrasion  from  the   spatulas  as  to 
communicate  so  much  matter  as  to  be  injurious  to  the  expe- 
riment.    In  these  cases  the  platinum  spatula  before  referred 
to  in  weighing  (62)   is  to  be  used,  and   hence  a  reason  for 
the  degree  of  thickness  and  strength  already  recommended. 

335.  When  the  substance  to  be  pulverized  is  coarse,  and 
its  quantity  unimportant,  a  piece  of  pasteboard  or  a  card  is 
very  useful  in  supplying  the  place  of  the  spatula,  in  clearing 
the  substance  from  the  mortar;  it  at  times  even  surpasses  it 
in  effect  and  convenience,  from  its  pliability  and  consequent 
adaptation  in  form  to  the  mortar,  and  also  from  the  larger 
quantity  which  it  will  lift  at  once.     Some  waste  cards  should 
always  be  ready,  in  one  of  the  laboratory  drawers,  for  these 
and  similar  uses. 

336.  Where  a  hard  substance  is  to  be  pulverized  for  the 
purpose  of  delicate  analysis,  it    is  sometimes  necessary  to 
take  into  account  the  matter  which  may  be  removed  from 
the  mortar  during  the  process,  and  estimate  its  influence  in 
increasing  the  quantity  of  products  ultimately  obtained.    In 
such  cases  a  mortar  of  known  composition  should  be  used, 
one  of  agate  for  instance,  where  the  substance  removed  may 
be  assumed  to  be  silica,  and  thus  the  correction  made  at  the 
proper  time,  by  subtracting  so  much  weight  from  the  silica 
evolved  in  the  analysis. 


*  Substances  easily  broken  up  are  most  expeditiously  reduced  to  coarse 
powder,  by  using  a  roller  of  wood  or  iron.  Chalk  or  ice  folded  up  in  a  napkin, 
is  thus  powdered  with  convenient  facility.— Ed. 

w 


170  PULVERIZATION DIAMOND. 

337.  It  is  highly  important  that  the  pupil  should  be  aware 
of  the  hygrometric  power  of  many  substances,  which,  when 
they  are  reduced  to  powder,  is  so  greatly  developed  by  the 
enlargement  of  surface,  as  very  seriously  to  increase  the  whole 
weight  of  the  substance.     M.  Pajot  Descharmes  says,  that  he 
has  had  an  increase  in  the  weight  of  rock  crystal  by  mere  pul- 
verization to  such   an  extent,  that  the  original   weight  was 
doubled^. 

338.  The  diamond  is  most  conveniently  pulverized  in  a 
steel  mortar,  having  a  cylindrical  chamber;  the  pestle  is  re- 
placed by  a  steel  cylinder  of  such  size  as  to  pass  easily  into 
the  cavity.     The  diamonds  are  first  introduced,  and  after- 
wards the  cylinder;  and  the  latter  being  struck  with  a  ham- 
mer, the  gems  are  crushed  and  reduced  to  powder  of  any  de- 
gree of  fineness  required,  without  the   risk  of  dispersion. 
When  first  used,  a  portion  of  diamond  is  lost,  as  it  were,  by 
adhesion    to   the   steel   surface :    this    should  be  left,   be- 
cause it  prevents  a  similar  loss  at  a  second  or  third  opera- 
tion.    Such  a  mortar  should  be  reserved  exclusively  for  the 
pulverization  of  these  gems ;  for,  besides  avoiding  a  repeti- 
tion of  the  loss  already  referred  to,  it  would  be  laborious 
and  difficult  to  clean   the  instrument  so  completely  from 
diamond,  that  if  sapphires,  for  instance,  were  afterwards  pul- 
verized in  it,  a  portion  of  diamond  should  not  be  mixed'with 
the  produce. 

339.  In  analysis  and  other  operations,  a  given  weight  of  a 
substance  in  powder,  as  100  or  200  grains,  is  often  required. 
This  quantity  should  not  be  first  weighed  out,  and  then  pul- 
verized, because  probably  a  little  loss  would  occur  during 
the  operation  from  adhesion  to  the  mortar,  and  to  the  trans- 
ferring tools;  but  more  than  the  weight  required  should  be 
reduced  to  powder,  and  when  in  a  proper  state,  the  exact 
quantity  should  be  weighed  out. 

340.  Pulverization  is  sometimes  useful,  not  for  the  pur- 
pose of  accelerating  chemical  action,  but  on  other  accounts. 
When  substances  are  to  be  heated  which  decrepitate  in  the 
fire,  by  which  portions  may  be  dispersed  and  lost,  the  effect 

*  Recueil  Industriel,  vii.,  64.     Quart.  Journ.  New  Series,  iv.,  425. 


SIFTING  POWDERS MIXING  BY  SIEVE.  171 

is  prevented  by  previous  pulverization.  Decrepitation  is 
generally  occasioned  by  the  expansion  of  the  outer  portions 
before  the  interior  has  had  time  to  heat,  and  in  that  respect 
resembles  the  breaking  of  a  glass  vessel  by  a  sudden  increase 
of  temperature.  By  comminuting  the  substance,  this  differ- 
ence in  different  parts  of  the  same  mass  is  avoided,  and  the 
body  sustains  the  heat  without  disturbance.  If  the  substance 
be  liable  to  a  similar  effect  from  included  moisture,  pulveri- 
zation, by  opening  passages  for  the  vapour,  is  equally  ef- 
fectual in  preventing  it*. 

341.  Pulverization  is  sometimes  effected  by  grinding  the 
body  under  a  muller,  upon  a  flat  stone ;  but  the  process, 
though  useful  in  some  of  the  arts,  especially  where  the  sub- 
stance is  to  be  mixed  with  fluid  into  a  paste,  is  so  inferior  to 
the  use  of  the  rnortar,  in  the  laboratory,  that  it  will  be  un- 
necessary to  describe  it  here. 

342.  It  seldom  happens,  perhaps  never,  that  the   opera- 
tions of  pulverization  reduce  the   body  into  a  powder  con- 
sisting of  particles  of  equal  size;  and   in  by  far  the  greater 
number  of  cases,  the   difference   between   them  is  evident. 
This,  though  of  no  conseqence  on   some  occasions,  renders 
it  necessary  on  others,  to  separate  the  mixture  of  differently 
sized   particles  into  portions  containing  such  as  more  nearly 
resemble  each  other  in  magnitude.     The  ordinary  and  well- 
known  operation  of  sifting  is  so  simple   as  to  require   no 
notice  here,  except  to   point  out  the  use  of  two  or  three 
sieves  in  the  laboratory,  which,  if  used  for  different  substan- 
ces, should  be  cleaned   after  every  operation,  either  by  a 
brush,  or,  which  is  better,  by  passing  a  stream  of  water  through 
them. 

343.  The  sieve  may  also  be  had  recourse  to  as  an  excellent 
means  for  effecting  the  mixture  of  powders,  provided  the  par- 
ticles are  of  such  size  as  to  pass  very  freely  through  it.     Two 
or  more  such  powders,  first  mingled  by  the  hand  or  a  spatula, 
and  then  passed  twice  or  thrice  through  the  sieve,  will  be  very 
uniformly  mixed. 

*  One  of  the  operations  the  most  dangerous  to  the  eyes,  is  that  of  adding  sulphu- 
ric acid  to  coarse  chlorate  of  potash  as  usually  directed  in  forming  the  paste  for 
making  quadroxide  of  chlorine.  The  projectile  effects  of  the  decrepitation  are 
entirely  obviated  by  reducing  the  chlorate  to  very  fine  powder. — ED. 


172  WASHING  OF  POWDERS. 

344.  Another  mode  of  separation,  in  very  frequent  use,  is 
that  of  washing  ;  for  as  light  and  minute  particles  are  sus- 
pended in  a  fluid,  whilst  the  larger  and   heavier  descend,  it 
thus  affords  a  ready  mode  of  separating  them.     This  opera- 
tion can  be  applied  to  few  bodies  except  such  as  are  insolu- 
ble in   water,  that   being  the  fluid   almost   constantly  made 
use  of.     It  may  often  be  conveniently  effected  in  tiie  mortar 
in  which  the  pulverization  itself  is  carried  on.     Suppose  a 
stone  were  to  be  reduced  to  powder,  no  particle  of  which 
should  be  less  than  of  a  certain  degree  of  fineness  :  the  stone 
should  be  pulverized  in  the  mortar  in  the  usual  manner,  and 
when,  from  the  appearance,  it  is  concluded  that  a  considera- 
ble  quantity    of  fine    powder   is   produced,  two-thirds   of 
the  mortar  should  be  filled  with  water,  and  the  powder  mix- 
ed well  up  in  it;  being  now  allowed  to  stand  a  very  short 
time,  until  the  particles  which  are  considered  as  too  coarse 
have   descended    to   the  bottom,  the  supernatant  mixture 
should  be  poured  off  into  a  large  basin  or  jar,  leaving  the 
heavy  powder  only  in  the  mortar,  with  a  little  water.     Then, 
without  adding  more  water,  or  endeavouring  to  remove  that 
which  is  still  present,  the  pestle  is  to  be   used   again,  until, 
from  the  ready  mixture  of  the  substance  with  the  water,  and 
the  production  of  a  smooth  soft  paste,  it  is  assumed  that 
much  more  of  it  has  "been  reduced  to  fine  powder.     Water 
is  to  be  added  to  wash  this  off  as  before,  the  finer  part  be- 
ing put  to  the  first  portion  separated ;  and  the  operator  is 
again  to  proceed  with  the  comminution  of  the  residuum  un- 
til it  has  in  this  manner  been  entirely   removed   from  the 
mortar. 

345.  If  by  this  process  the  powder  be  sufficiently  reduced, 
and  a  greater  regularity  as  to  size  amongst  its  particles  be 
not  required,  then  the  mixture  of  it  with  water  should  be  left 
quiescent  until  the  liquid  be  clear,  and  the  powder  in  mass 
form  a  stratum  beneath.     The  former  should  then  be  poured 
off,  and  the  latter  dried  ;  and  if  during  desiccation  it  adheres 
and  produces  soft  lumps,  these  are  easily  broken  down  in 
the  mortar. 

346.  If,  on  the  contrary,  more  uniformity  in  the  powder  be 
required  than  is  thus  obtained. by  a  first  set  of  operations,  it 


OTHER  MODES  OF  WASHING IN  A  MORTAR.       173 

may  be  effected  by  a  second,  and  this  will  often  be  neces- 
sary when  the  substance  pulverized  is  such,  that  a  very  short 
period  only  can  be  allowed  for  the  deposition  of  the  larger 
particles ;  for  the  motion  of  the  water  not  having  subsided, 
and  being  unequal  in  different  parts,  some  large  particles  will 
pass  over  with  the  finer.  In  such  cases  a  return  of  the  mat- 
ter to  the  mortar,  and  a  repetition  of  the  washing,  will  fre- 
quently separate  much  of  the  substance  that  requires  further 
trituration.  This  second  washing  need  not  be  deferred  till 
the  whole  has  settled  from  the  water  of  the  first  washing ; 
but  all  being  stirred  together,  and  allowed  to  stand  for  rather 
a  longer  period  than  before,  the  suspended  portion  may  then 
be  poured  off,  and  the  rest  operated  with  as  directed  (344). 
The  longer  the  period  allowed  for  subsidence,  so  much  the 
finer  will  be,  the  particles  still  remaining  in  suspension,  and 
hence  an  easy  process  for  obtainingthe  substance  in  powder 
divided  to  any  degree  required. 

347.  Another  method  of  washing  is  to  use  a  small  mortar, 
and,  after  having  powdered  the  dry  substance  in  the  usual 
way,  to  place  the  vessel  in  a  large  strong  dish,  and  then,  di- 
recting a  small  stream  of  water  into  it,  to  continue  trituration 
in  a  steady,  slow  manner.     The  water,  after  filling  the  mor- 
tar, will  flow  over  into  the  basin,  carrying  the  smaller  parti- 
cles with  it ;  and  as  the  trituration  proceeds,  the  current  will 
continually  separate  the  finer  part,  until  the  whole  has  passed 
from  the  mortar  into  the  dish.     The  fineness  of  the  particles 
washed  over  is  regulated  by  the  depth  of  the  mortar,  the  size 
and  force  of  the  current,  and  the  degree  of  agitation  given  by 
the  pestle  in  grinding.     To  insure  a  powder  of  considerable 
uniformity,  the  operation  should  be  repeated  as  before  de- 
scribed (346). 

348.  The  same  principles  and  processes  may  be  applied  to 
the  separation  of  insoluble  substances  of  different  specific 
gravities.     If  an  ore  contain  metallic  silver  diffused  through 
an  earthy  matrix,  the  processes  of  pulverization  and  washing 
will  almost  entirely  separate  the  earths  from  the  metal.     Or 
if  platinum  ore  be  treated  in  the  same  way,  a  separation  of  the 
iridium  and  osmium,  and  other  substances,  from  the  grains  of 
metal,  may  in  this  simple  manner  be  effected  to  a  great  ex- 
tent, and  the  platinum  very  much  cleansed. 


174  WASHING  WITH  OIL SILICA GRANULATION. 

349.  It  is  rarely  that  any  other  washing  agent  than  water 
is  had  recourse  to  ;  but  in  peculiar  cases,  and  for  sma  llquan- 
tities  of  matter,  oil  may  be  used.     From  its  tenacity  it  re- 
quires a  longer  portion  of  time  before  deposition  takes  place, 
and  the  division  may  consequently  be  more  accurately  effec- 
ted.    It  may  be  burnt  off  so  as  to  be  entirely  removed  from 
the  powder,  provided  the  latter  be  of  such  a  nature  as  not  to 
be  effected  by  the  single  or  joint  action  of  oil  and  heat. 

350.  If  silica  be  required  in  a  state  of  extreme  division,  it 
may  be  obtained  by  mixing  (343)  one   part   by  weight  of 
finely  pulverized  flint  glass,   with  two  parts  of  pulverized 
white  marble,  heating  the  mixture  to  bright  redness  for  half 
an  hour,  rubbing  it  in  the  mortar  and  again  heating  it;  then 
acting  upon  it  in  an  evaporating  dish  (369)  by  muriatic  acid 
added  till  in  slight  excess,  evaporating  to  dryness  (592),  and 
redissolving  in  warm  water  with  a  little  muriatic  acid.     The 
insoluble  portion  is  to  be  well  washed  in  abundance  of  pure 
water,  until  free  from  salts  of  lime  or  lead,  and  being  then 
dried,  the  silica  will  be  in  a  state  of  division  far  surpassing 
any  which  can  be  obtained  merely  by  mechanical  means. 
The  alkalies  cannot  be  used  in  place  of  lime  or  its  carbo- 
nate, for  this  purpose,  for  portions  of  them  remain  combined 
with  the  silica. 

351.  Of  the  metals,  all  that  are  brittle  may  be  pulverized. 
The  division  of  zinc  in  this  way  when  hot  has  been  before 
mentioned  (332).     Some  metals  may  be  obtained  in  a  use- 
ful state  of  division  by  granulation.     This  is  particularly 
the  case  with  zinc,  copper,  tin,  and  lead.     For  this  purpose, 
the  metal  is  to  be  melted  in   a  crucible,  and  then  poured 
from  a  height  of  two,  three  or  four  feet,  into  a  pail  or  pan, 
full  of  water:  a  considerable  depth  of  water  should  be  allow- 
ed, as  the  slight  explosions,  which  sometimes  happen,  are 
then  less  likely  to  take  place.     If  the  water   be  hot,  the 
pieces  become  filmy  and  blown  up  as  it  were  into  bubbles; 
if  cold,  they  have  more  solidity,  are  smaller,  and  approach 
nearer  in  their  form  to  shot,  differences  which  are  dependent 
also  in  part  on  the  temperature  of  the  metal  itself.     The 
crucible  should  be  moved  during  the  time  the  metal  is  run- 
ning from  it,  that  the  .descending  stream  may  continually 
change  its  place  in  the  water. 


LAMINATION FILING.  175 

352.  Some  metals  are  brought,  by  lamination,  into  a  state 
equally  advantageous  for  chemical  action  from  the  extent  of 
surface  exposed,  as  that  produced  by  pulverization;  and  the 
process  is  applicable  in  cases  when  the  latter  cannot  be  re- 
sorted to.    Thus  platinum,  tin,  lead,  zinc,  copper,  gold,  and 
silver,  are  obtained  in  the  state  of  foil;  platinum,  gold,  and 
silver,  in  the  state  of  leaf;  and   are  highly  advantageous  in 
certain  experiments,  when  thus  attenuated.     The  chemical 
action  which  takes  place  between  platinum  and  tin  is  in  no 
way  so  effectually  exerted,  or  so  advantageously  shown,  as 
when  pieces  of  each  metal  in  the  state  of  foil  are  laid  to- 
gether, folded  up  into  a  ball,  and  heated  red  hot.*     They 
combine  in  that  case  with  such  force  as  to  produce  vivid 
combustion. 

353.  The  same  advantage,  dependant  upon  extension,  is 
obtained  to  a  considerable  degree  by  drawing  the  ductile 
and  tenacious  metals  into  wire,  their  state  being  then  for 
many  purposes  equivalent  to  that  of  actual  division.     Pure 
iron,  which  would  resist  the  processes  already  described,  is 
successfully  attenuated  in  this  way. 

354.  At  other  times  the  tough  and  ductile  metals,  as  well 
as  some  others,  may  be  divided  by  the  action  of  the  file. 
In  such  cases  the  files  should  be  very  clean.     If  new$  atten- 
tion should  be  paid  to  the  oil  with  which  they  are  in  that 
state   generally  covered.     If  they  have  been  used,  the  ab- 
sence of  dirt,  metals,  or  other  substances,  from  between  the 
teeth,  should   be  ascertained  and  secured,  and  the  clean 
state  of  the  surface  upon  which  the  filings  are  to  fall,  should 
not  be  forgotten.     Iron  and  zinc  are  most  generally  requir- 
ed in  the  state  of  filings. f 

355.  Occasionally  metals  may  be  divided  into  small  par- 
ticles by  being  fused,  and  then  poured  into  a  wooden  box 
and  well  shaken  until  solid  and  much  cooled.     Zinc,  lead, 

*  The  neatest  mode  of  performing  this  experiment  consists  in  laying  platinum 
foil  above  tinfoil,  on  a  charcoal  support,  and  throwing  on  the  platinum  a  down- 
ward jet  of  hydrogen.— ED. 

f  By  means  of  a  magnet  iron  filings  may  be  separated  from  coarse  and  inad- 
hesive impurities.  The  oil  is  removable  by  lime  water,  in  which  the  filings  do 
not  become  oxidized.— Ed. 


176  CHEMICAL  MEANS  OF  DIVISION. 

tin,  antimony,  &c.,  may  be  so  pulverized,  but  usually  a  p/£rt 
of  the  charred  wood  is  mixed  with  the  metal,  and  the  sur- 
face of  the  particles  is  generally  oxidized.  This  method 
should  be  used  only  when  no  other  is  applicable  or  attain- 
able. 

356.  Silver,  copper,  gold,  platinum,  and  lead,  may  be  use- 
fully divided  by  chemical   means — silver,  by  introducing  a 
plate  of  copper  into  a  solution  of  acid  nitrate  of  silver,  until 
about  one-half  or  three-fourths  are  precipitated,  the  metal 
not  being  allowed  to  accumulate  upon  the  copper,  but  shak- 
en off  from  time  to  time,  and  at  last  (removing  the  copper 
plate  and  solution)  washed  with  distilled  water  until  tasteless, 
and  then  dried.     Copper  may  be  prepared  in  the  same  man- 
ner by  immersion  of  a  plate  of  iron  in  a  solution  of  sulphate 
of  copper  with  a  little  sulphuric  acid,  added  to  it,  and  should 
afterwards  be  washed  with  dilute  sulphuric  acid,  then  with 
water  and  finally  dried.     Gold  may  be  prepared  in  very  fine 
powder  by  adding  a  solution  of  proto-sulphate   of  iron  to 
one  of  muriate  of  gold,  and  then  washing  with  a  little  muri- 
atic acid  and  pure  water.     Platinum  is  procured  in  a  state  of 
extreme  division,  though  the  particles   adhere  slightly  to- 
gether, by  heating  the  ammonio-muriate  of  platinum  to  dull 
redness  in  a  crucible,  until  fumes  cease  to  rise.     It  has  the 
appearance   of  a  sponge,  though  perfectly  metallic.     By 
heating  the  tartrate  of  lead  in  a  close  vessel,  or  a  tube,  to 
dull  redness,  a  mixture  of  charcoal  and  lead  is  obtained,  in 
which  the  latter  is  in  such  an  extreme  state  of  division,  that 
on  exposure  to  the  air  it  takes  fire.     It  is  the  pyrophorus  of 
Dr  Gobel,  and  seems  to  owe  its  property  only  to  the  state 
of  division  of  the*  metal;  the  action  of  oxygen,  which  in  ge- 
neral is  merely  sufficient  to  tarnish  the  surface  of  lead,  being 
here,  from  the  comparative  absence  of  all  solidity,  and  the 
existence  of  surface  to  an  almost  infinite  extent,  so  simulta- 
neously exerted  upon  every  particle  as  to  cause  ignition. 

357.  Organic  substances,  which  are  not  sufficiently  brit- 
tle to  admit  of  pulverization,  such  as  wood,  horn,  &c.,  may 
be  cut,  or  crushed,  or  rasped,  or  grated,  according  to  cir- 
cumstances; a  division  sometimes  gross,  sometimes  minute, 
being  required. 


SOLUTION USES  OF TWO  KINDS.  177 

SECTION  VI. 
SOLUTION,  INFUSION,  DIGESTION,  &c. 

358.  THERE  are  two  greatand  general  objects  to  be  gained 
by  solution,  which  render  it  a  process  of  constant  occur- 
rence in  the  laboratory.     The  first  is  that  of  preparing  sub- 
stances for  the  exertion  of  chemical  action ;  and  from  the 
perfect  manner  in  which  it  separates  the  particles  one  from 
another,  every  obstacle  dependant  upon  the  attraction  of 
aggregation  is  removed,  at  the  same  time  that  other  advan- 
tages are  obtained  (306)-:  the  second  object  is  that  of  sep- 
arating one  substance  from  another;  this  being  continually 
effected  by  the  use  of  such  fluids  as  have  a  solvent  power 
over  one  or  more  of  the  substances  present. 

359.  These  great  uses  of  solution   render  it  proper  to 
show  the  means  by  which  to  effect  and  facilitate  it;  in  what 
manner  to  select  the  vessels  and  solvents  ;  and  to  point  out 
any  peculiar  circumstances  or  conditions  attending  it,  which 
may  assist  the  process.     But  it  will  be  right  to  premise  that 
the  solution  here  to  be  considered  relates  almost  always  to 
solid  matter,  sometimes  to  liquid  matter,  but  not  at  all  to 
gaseous  substances ;  for  any  processes  or  directions  for  the 
solution  of  gases  in  liquids  will  be  more  intelligibly  and  in- 
structively considered  in  the  section  on  gaseous  manipula- 
tion.     Indeed   the   processes  requisite  are  so  different  to 
what  are  here  to  be  described,  as  of  themselves  to  suggest 
the  propriety  of  the  separation.     The  course  of  this  section 
will  be  generally  from  inorganic  to  organic  substances ;  for 
in  that  way  the  simplest  instances  and  methods  will  come 
first  into  view. 

360.  It  may  be  remarked  at  the  outset,  that  solution  is 
of  two  kinds,  being  effected  either  by  fluids  which  have  no 
chemical  action  upon  the  substances  to  be  dissolved,  or  by 
others  which  have  such  an  action  ;  both  are  of  constant  use 
in  the  laboratory.     For  where,  as  very  often  happens,  sol- 
vents of  the  first  kind  fail,  recourse  must  be  had  to  the  lat- 
ter, and  then  much  care  and  judgment  is  required  in  the  se- 

X. 


178  SOLUBILITY INDICATIONS. 

lection  of  those  which  will  best  effect  the  desired  en%d.  At- 
tempts have  been  made  to  distinguish  between  these  two 
methods,  by  the  use  of  the  terms  Solution  and  Dissolution, 
but  they  have  been  partial  and  imperfect,  and  chemical 
works  now  constantly  speak  of  solution  of  the  metals,  of 
earths,  &c.,  and,  therefore,  virtually  reject  the  distinction. 

361.  Water  is  the  great  solvent  whose  aid  is  first  to  be 
called  in ;  others  are  to  be  resorted  to  only  when  that  is  in- 
sufficient.    So  general  and  important  is  its  use,  that  in 
speaking  simply  of  the  solubility  of  a  body,  water  is  always 
understood  to  be  referred  to.     All  aqueous  solutions  of  solid 
bodies   are   heavier   than   watery  upon   this  difference  is 
founded  a  very  convenient  indication  of  solubility,  frequent- 
ly useful,  always  easy.     It  is  to  suspend  a  piece  of  the  sub- 
stance in  a  glass  of  clear  undisturbed  water  ;  if  the  body  be 
soluble,  a  descending  current  will  be  seen  to  fall  from  it, 
and  be  visible  upon  looking  through  the  water  horizontally. 
If  it  fall  rapidly  and  in  dense  striae,  it  will  indicate  rapid 
solubility,  and  the  formation  of  a  dense  solution  ;  if  it  fall  in 
a  very  narrow  stream,  it  will  indicate  only  moderate  or  slight 
solubility;  and  by  its  descending  rapidly  or  in  a  slow  broad 
stream,  or  by  resting  about  the  substance,  a  judgment  may 
be  made  of  the  comparative  density  of  the  solution  produced. 
If  no  descending  current  appear,  nor  any  fluid-round  the 
substance  of  a  refractive  power  or  colour  different  to  that  of 
the  water,  then  the  body  must  be  very  nearly  if  not  quite 
insoluble  at  common  temperatures. 

362.  Another  indication  of  solubility  is  gained  from  the 
taste.   The  saliva  in  the  mouth  is,  as  to  mere  solubility,  nearly 
the  same  as  water,  and,  generally  speaking,  those  substances 
which  are  most  sapid  are  most  soluble.  *The  impression  of 
taste  in  the  mouth  is,  however,  frequently  a  mixed  sensation, 
being  dependent  in  part  upon  the  olfactory  nerves;  and  con- 
sequently odorous  bodies  will  frequently  appear  to  be  highly 
sapid,  when  they  are  not  so  upon  the  tongue*.    This  is  the 
case  with  camphor,  which,  if  taken  into  the  mouth,  after  the 
nostrils  have  been  perfectly  closed  by  the  fingers,  so  that  no 

*  Chevreul,  Memoires  du  Musee,  x.  439. 


SIGNS  OF  SOLUBILITY.  179 

air  can  pass  through  them,  will  seem  to  have  little  or  no  taste, 
whereas,  the  moment  the  fingers  are  removed,  and  the  aroma 
has  access  to  the  olfactory  nerves,  an  intense  taste,  using  the 
word  in  its  ordinary  acceptation,  is  perceived.  A  similar 
effect  may  be  observed  with  a  peppermint  lozenge  or  a  piece 
of  chocolate.  Still,  however,  the  indication  may  in  many 
cases  be  useful,  and  has  the  advantage  of  requiring  no  appa- 
ratus, and  being  easy  of  performance. 

363.  If  the  substance  appear  to  be  insoluble,  or  if  it  be 
necessary  to  know  whether  it  be  soluble  in  alcohol,  ether, 
oils,  or  any  other  body,  for  the  purpose  of  selecting  a  solvent 
from  among  them,  a  portion  should  be  pulverized  finely,  and 
introduced  into  a  small  tube,  with  a  little  of  the  fluid,  to  be 
tried,  and  heated  ;  if  the  substance  disappear,  it  is,  of  course, 
soluble.     But  if  it  be  supposed  to  be  a  mixed  body,  and  partly 
soluble,  though  not  altogether  so,  then  the  presumed  solution 
should  be  poured  from  the  tube  into  an  earthenware  or  pla- 
tinum capsule,  and  evaporated  carefully  and  slowly;  if  any 
substance  remain,  it  of  course  indicates  solubility.     Trials  by 
evaporation  cannot  be  made  with  oil  unless  the  body  be  fixed 
and  will  allow  the  oil  to  be  burned  off;  nor  can  trials  of  very 
volatile  bodies  be  made  in  this  manner.,    It  is  almost  need- 
less to  add,  that  cases  may  occur  requiring  much  chemical 
skill  and  judgment ;  and  that  it  would  be  impossible  to  give 
directions  for  every  possible  occasion. 

364.  Indications  of  solution  dependant  upon  chemical  ac- 
tion are  obtained  from  the  changed  appearance  of  the  sub- 
stance.    A  body  not  soluble  in  water  except  by  the  use  of 
acids  or  alkalies,  is  generally,  though  not  always  rendered 
so  by  chemical  action,  and  has  its  properties  changed.     It  is 
rarely  that  these  chemical  agents  are  applied  with  any  other 
liquid  than  water.     Indications  of  their  power  may  be  ob- 
tained in  the  manner  before  directed. 

365.  With  regard  to  the  solution  of  one  liquid  in  another, 
no  difficulty  will  occur  in  ascertaining  whether  it  takes  place 
or  not.     A  small  portion  of  the  most  valuable  should  be  put 
into  a  tube,  and  then  a  very  little  of  the  other  added  to  it; 
agitation,  followed  by  rest,  will  show  whether.the  two  have 
permanently  mixed,  or  whether  they  separate  again.     If  the 


180  SOLUTION HEAT VESSELS. 

latter  be  the  case,  let  further  portions  of  the  second  liquid  be 
added,  agitating  and  observing  as  before  ;  and  this  should  be 
done  until  the  whole  becomes  one  clear  fluid,  or  until  the 
volume  is  increased  to  many  times  its  former  bulk.  A 
conclusion,  according  to  the  state  of  things,  must  then  be 
made. 

366.  It  may  here  be  proper  to  warn  the  student  of  an 
appearance  which  sometimes  takes  place  during  mere  solu- 
tion, which  has  been  frequently  misconstrued  into  an  indica-. 
tion  of  chemical  action.     Common  salt,   and  several  other 
salts,  as  well  as  their  strong  solutions,  and  also  alcohol  or 
spirit  added  to  common  or  even  distilled  water,  which  has 
been  exposed  to  air,  frequently  causes  the  evolution  of  a 
number  of  small  air  bubbles  ;  these  have  the  appearance  of 
being  the.  direct  result  of  some  chemical  action,  but  are  oc- 
casioned merely  by  the  expulsion  of  the  air  dissolved  in  the 
water,  which  being  incompatible  with  the  substances  added, 
is  separated.     Some  of  those  solutions  which  dissolve  air, 
produce  the  same  appearances  when  added  to  the  bodies 
mentioned. 

367.  Whenever  a  dissolving  power  exists  at  common,  tem- 
peratures, it  is  generally  heightened,  and  sometimes  to  a 
great  degree,  by  an  elevation  of  temperature.     There  are 
only  two  known  cases  in  which  heat  diminishes  the  effect; 
these  occur  with  lime  and  magnesia.*    But  there  is,  I  be- 
lieve, no  instance  of  a  body  not  soluble  at  common  tempera- 
tures being  rendered  so  by  the  mere  application  of  heat:  it 
is  the  quantity  of  effect  only,  and  not  its  existence,  that  is 
thus  influenced.     The  change  is,  nevertheless,  very  impor- 
tant, as  favouring  and  facilitating  the  desired  object :  and 
comminution  is  also  of  great  value  preparatory  to  solution, 
for  the  same  reason. 

368.  The  vessels  required  in  the  laboratory  for  the  pur- 
poses of  solution  are  numerous.     They  should  be  competent 
to  resist  the  action  of  heat,  acids,  alkalies,  all  aqueous  solu- 
tions, and,  for  convenience,  should  as  often  as  possible  be 


SOLUTION BASINS CAPSULES.  181 

transparent.  Hence  the  necessity  of  a 
dozen  or  two  of  glasses;  they  should  al- 
ways be  lipped,  and  ale  glasses  will  answer 
the  purpose  very  well.  Glass  jars  will  al- 
so be  required,  and  are  best  of  the  form 
depicted  in  the  wood  cut  (5b5),  as  they 
then  answer  other  purposes,  to  be  referred  to  in  Section 
VIII.  They  should  be  from,  one  to  two  or  three  pints  in 
capacity. 

369.  Lipped  earthenware  basins,  from  li  to  10  inches  in 
diameter,  are  also  necessary.     They  should  be  tried  by  a 
solution  of  muriate  of  iron,  or  sulphate  of  copper,  both  on 
the  glazed  and  unglazed  part,  in  the  manner  directed  with 
respect  to  mortars  (309),  for  which  purpose  a  little  of  the 
solution  should  be  put  into  one  basin,  a  smaller  basin  dip- 
ped into  it,  and  heat  applied.     A  strong  solution  of  sulphate 
of  indigo  and  an  infusion  of  logwood  are  also  good  agents 
to  try  them  with.     The  basins  should  be  quite  <dry  when 
put  into  them,  and  after  being  boiled  in  the  colouring  fluid 
should  immediately  wash  clean  in  water.     Basins  which  will 
stand  a  trial  of  this  kind  are  in  that  respect  excellent;  and 
I   have  recently   obtained   such  from  Messrs  Wedgwood's 
manufactory. 

370.  If  such  as  these  cannot  be  obtained,  those  of  more 
moderate  quality  must  suffice.     Of  whatever  kind  they  be, 
they  should  resist  the  action  of  acids  and  alkalies  in  solu- 
tion.    They  should  also  be  chosen   thin  rather  than  stout 
and  thick,  though  some  of  both  are  desirable  ;  but  when  in- 
tended to  sustaifi  the  application  of  heat,  the  thinner  they 
are  the  better,  so  that  they  have  sufficient  strength  to  bear 
safely  the  utmost  weight  of  fluid  they  can  contain.     Chemi- 
cally considered  it  is  desirable  that  they  should  be  made 
very  thin  at  the  bottom,  and  thicker  at  the  sides,  they  then 
stand  the  sudden  application  of  heat  much  better  than  if 
thick  at  the  bottom.     Their  greater  liability  to  mechanical 
injury  must  be  guarded  against  by  increased  care. 

371.  A  dish  or  two  made  of  pure  silver,  and  a  few  platinum 
capsules,  are  also  necessary.     They  should  have  a  project- 
ing tongue  of  metal  to  serve  as  a  handle  by  which  they  may 


1 82  FLASKS — FLINT-GLASS — FLORENCE. 

be  held  with  a  pair  of  pincers.  The  silver  dishes  may  be  as 
large  as  can  be  permitted  up  to  six  inches  in  diameter. 
The  platinum  capsules  should  be  about  li  or  2  inches  in 
diameter.  Very  useful  glass  dishes  and  capsules  are  made 
out  of  old  retorts,  receivers,  and  flasks,  in  the  manner  to  be 
described  hereafter  (1212);  and  they  will  admit  of  the  ap- 
plication of  heat  carefully  applied.  It  is  not  advantageous 
to  purchase  glass  dishes  for  the  preparation  of  solutions  ; 
they  are  so  brittle  and  liable  to  fracture  from  heat,  as  to  be 
both  expensive  and  dangerous  to  the  experimenter's  results. 

372.  JFlasks  are  very  useful.     Those  made  of  flint  glass 
should  vary  from  an  ounce  to  a  quart  in  capacity;  the  neck 
should  expand  at  the  mouth,  or  a  projecting  ring  should  be 
formed  on  it,  that  the  flask  may  be  held  safely  by  that  part 
without  danger  of  slipping.     They  should  be  examined  with 
respect  to  thickness,  and  the  most  uniform  should  be  chosen; 
provided  they  be  not  so  thick  as  to  be  liable  to  rupture  by 
heat,  or  s«p  thin  as  to  burst  by  the  weight  of  the  fluid,  or  by 
handling  when  filled.    The  thinnest  that  are  of  sufficient 
strength  should  be  selected.     The  bottoms  should  be  par- 
ticularly observed :  they  are  frequently  much  thicker  than 
the   other  parts,    and  then  almost  invariably  break  when 
placed  upon  the  sand  bath  or  over  a  lamp.     The  thickness 
of  a  flint-glass  flask,  from  half  a*  pint  downwards  in  size, 
should  be  about  that  of  an  ordinary  Florence  flask :  when 
larger  they  should  be  somewhat  thicker.     The  indications 
by  which  irregular  or  excessive  thickness  is  judged  of  are 
dependant  upon  peculiar  appearances  of  the  reflection  and 
refraction  of  Jjght,  and  are  best  .learned  from  an  ocular  ex- 
amination of  a-good  and  of  a  decidedly  bad  flask. 

373.  Florence  flasks  are  very  useful  vessels,  and  for  most 
purposes  are  superior  to  flint-glass  flasks.     They  are  always 
thin,  and  require  careful  handling  when  filled  with  a  fluid,  or 
they  will  be  crushed  from  the  attempt  to  support  the  weight. 
If  resting  upon  the  bottom  they  should  be  supported  by  a 
large  surface  (68).     It  is  seldom  that  they  are  knotty,  but 
should  that  be  the  case,  the  flask  ought  not  to  be  subjected 
to  the  action  of  heat,  lest  it  should  fly.     Liquids  should  never 
be  put  into  a  cracked  flask  or  glass  vessel,  for  the  purpose  of 


I 

SOLUTION-BODS DETAIL  OF  PROCESS.  183 

being  heated.  Florence  flasks  maybe  obtained  of  two  sizes, 
by  application  to  oilmen,  or  to  foreign  wine-merchants  :  the 
pints  having  been  used  to  contain  olive  oil,  the  quarts  to 
hold  wine*. 

374.  Besides  these  vessels,  stirrers  are  frequently  required 
in  the  progress  of  these  operations.    They  should  be  made 
of  solid  glass  rod,  and  not  of  tube.     The  diameter  may  vary 
from  the  quarter,  to  the  one-third  of  an  inch  ;  the  length  from 
six  to  ten  inches.     After  being  cut  off  from  the  glass  rod, 
the  etids  should  have  tlie  sharp  edge  round  them  removed  by 
a  fine,  or  a  dull  file ;  or  they  should  be  softened  in  the  blow- 
pipe flame  (1154),  and  in  that  case  some  should  be  left 
round  at  the  extremities,  and  others  conical,  each  having  its 
particular  uses  (70).     Mr  Phillips  bends  them  very  slightly 
in  the  blow-pipe  flame,  which  prevents  their  rolling  off  the 
table.     Enamel  rod  is  sometimes  used  for  this  purpose,  but 
glass  is  harder  and  not  so  brittle.     Thick  glass  tube  is  not 
good,  because  the  sealed  end  is  apt  to  crack  off  in  hot  solu- 
tions, and  then  the  cavity  opened  is  a  receptacle  for  dirt. 

375.  All  these  utensils  are  equally  useful  for  evaporation 
and  other  processes,  as  for  solutions,  requiring  in  these  cases 
generally  no  other  qualities  than   those  before  mentioned. 
This  being  understood  they  will  not  be  referred  to  again. 

Proceeding  now  to  the  operations  of  solution,  the  following 
method  is  very  ready,  and  of  constant  use  in  the  laboratory 
relative  to  salts  and  similar  substances,  which  are  entirely 
soluble,  and  form  a  solution  of  sufficient  strength  without 
the  application  of  heat.  The  substance  should  be  put  into 
a  clean  mortar,  a  little  water  be  added,  and.  by  the  action 
of  the  pestle  the  solid  matter  reduced  to  a  thin  paste  ;  this  is 
done  in  a  few  moments,  more  water  should  then  be  added, 
and  the  whole  stirred  together,  in  consequence  of  which  the 
finest  particles  will  rapidly  disappear.  When  upon  contin- 
uing the  trituration,  the  fresh  portion  of  small  powder  which 
is  produced  does  not  seem  to  dissolve,  the  whole  should  be 


*  When  Florence  flasks  are  to  be  closed  by  corks,  the  upper  part  of  the  nqcks 
should  be  supported  by  wrappers  of  waxed  twine  ;  otherwise  they  will  not  bear 
the  operation  well. — ED. 


184  SOLUTION— FACILITIES. 

allowed  to  stand  a  moment,  the  fluid  poured  into  a  glass  or 
jar,  the  residuum  triturated,  water  added,  and  the  process 
continued  until  the  whole  is  dissolved.  The  solution  when 
all  together  should  stand  a  few  minutes,  to  deposit  any  mi- 
nute particles  that  may  not  have  been  dissolved ;  or  a  little 
water  added  to  it,  and  the  whole  agitated,  when  it  will  im- 
mediately become  clear  or  nearly  so.  If  there  be  occasion 
it  should  then  be  filtered,  and  in  this  way  a  solution  nearly 
saturated,  and  always  strong  enough  for  ordinary  laboratory 
uses,  may  be  made  in  a  few  minutes. 

376.  This  method  of  facilitating  solution  by  mechanical 
division  is  very  useful  in  numerous  cases.     If  one  substance 
be  embarrassed  or  enveloped  by  another,  it^ffi  thus  more 
easily  exposed  t6  the  solvent;  and^from  the  Peat  utility  of 
this  practice  when  chemical  solvents  are  used,  as  acids  or 
alkalies,  arises  the  necessity   of  having  mortars  which  are 
competent,  as  before  mentioned  (309),  to  resist  the  action 
of  these  and  similar  substances. 

377.  The  use  of  heat  in  assisting  solution  is  very  great,  and 
though  heat  and  division  may  in  many  cases  be  resorted  to 
almost  indifferently  for  effecting  the  required  end,  yet  the 
student  should  understand  that  they  attain  the  object  in  dif- 
ferent ways,  that   he  may  know  in  peculiar  cases  when  to 
apply  the  one  and  when  the,  other.     Division  is  favourable 
merely  by  increasing  the  surface  of  contact  between  the  sol- 
vent and  the  body  to  be  dissolved ;  thus  offering  an  immense 
number  of  points  where  tbe  action  may  simultaneously  be 
exerted, 'and  in  this  way  bringing  it  sooner  to   a  close: 
whereas  heat  acts  directly  by  increasing  the  power  of  the 
solvent,  and  enabling  it  to  take  up  a  larger  quantity,  and  in- 
cidentally by  causing  a  multitude  of  currents  in  the  liquid, 
by  which  fresh  portions  are  continually  brought  into  contact 
with  the  body  to  be  dissolved.     Hence  heat  does  not  merely 
expedite  the  action,  and  in  that  way  do  what  comminution  ef- 
fects ;  but  it  does  actually  increase  it,  and  cause  a  greater 
portion  of  the  solid  body  to  be  dissolved  than  would  other- 
wise be  the  case. 

378.  Perhaps  the  simplest  application  of  heat  is  that  re- 
quired to  obtain  a  solution  saturated  when  cold.     It  would 


TEST  OF  SATURATION.  185 

take  a  long  time,  for  instance,  to  prepare  a  saturated  aqueous 
solution  of  white  arsenic,  by  contact  of  the  powder  with 
water,  or  even  by  agitation;  but  by  boiling  the  water  with 
the  powder  for  half  an  hour,  leaving  it  to  cool,  and  after- 
wards filtering  it,  a  saturated  solution  will  be  immediately 
obtained.  The  same  is  the  case,  though  not  so  strikingly, 
with  more  soluble  substances,  as  sulphate  of  potash,  nitre, 
&c.,  and  in  these  instances  the  object  is  generally  effected 
by  warming  the  pulverized  substance  with  the  water  in  an 
evaporating  basin  or  flask,  over  a  lamp  or  sand-bath,  or  by 
using  warm  water  with  trituration  in  the  mortar.  With  the 
exception  of  the  two  or  three  salts  which  are  scarcely  more 
soluble  in  hot  water  than  in  cold,  the  attainment  of  the  ob- 
ject should  be  ascertained  by  observing  whether  the  hot  so- 
lution has  deposited  any  portion  of  the  solid  substance  du- 
ring its  cooling  :  if  it  has,  it  proves  the  saturation,  if  it  has 
not,  there  is  reason  to  doubt  it,  and  heat  with  more  of  the 
solid  substance  in  powder  should  again  be  applied. 

379.  An  easy  method  of  testing  this  point  of  saturation, 
even  whilst  the  solution  is  hot,  is  to  dip  a  glass  rod  into  the 
liquor,  and  by  means  of  it  to  transfer  a  drop  to  a  cold  glass 
plate  (1348) :  if  a  deposition  of  crystals  or  solid  substance 
appear  in  a  few  moments,  then  the  solution  will  be  satura- 
ted when  cold.     If  they  do  not  appear  immediately,  still  the 
student  should  not  be  satisfied,  until  he  has  stirred  the  drop 
with  the  platina  spatula,  and   repeatedly  struck  the  glass 
beneath   the  solution  with  the  metal ;  this  will  frequently 
cause  a  precipitation  of  crystals  to  take  place,  which  would 
not  otherwise  have  appeared  except  in  a  long  time,  and  they 
equally  indicate  that  the  solution  when  cold  will  be  satura- 
ted.   Ultimately  the  solution  should  be  filtered,  if  necess- 
ary, to  separate  any  mechanical  impurity. 

380.  When  the  object  of  applying  heat  to  increase  the 
solvent  power  is  not  simply  to  obtain  a  saturated  solution, 
but  to  accelerate  a  process  which,  either  from  the  previous 
combination  of  the  substance  with  other  bodies,  or  the  want 
of  action  at  ordinary  temperatures,  would  be  tedious  and 
imperfect,  if  not  urged  by  all  the  means  at  command  ;  the 


186  SELECTION  OF  VESSELS. 

application  has  to  be  continued  for  a  longer  time,  and  fre- 
quently in  vessels  which  will  retain  the  vapour  more  per- 
fectly than  a  basin.  The  ebullitions  and  digestions  which 
are  sometimes  continued  for  a  long  period,  are  processes  of 
this  kind,  and  the  choice  of  the  vessel  will  depend  upon  the 
circumstances  attending  the  action.  Basins  and  open  ves- 
sels are  convenient,  because  they  afford  a  ready  access  to 
the  liquid,  either  for  the  purpose  of  removing  portion's  for 
examination  when  necessary,  or  for  stirring  and  agitation. 
For  this  reason,  when  the  dispersion  of  a  little  vapour,  or 
even  of  a  little  of  the  substance  by  ebullition  is  of  no  con- 
sequence, basins  are  very  convenient,  and  they  are  necessari- 
ly used  when  the  substances  are  operated  upon  in  such  a 
form  as  prevents  their  introduction  Into  flasks.  But  when 
it  is  desirable  to  retain  the  vapour  as  much  as  possible,  as 
whilst  using  acids,  or  when  it  is  necessary  that  all  loss  from 
ebullition  be  avoided,  or  all  possible  contact  of  extraneous 
substances  prevented,  then  flasks  are  most  useful,  and  es- 
pecially Florence  flasks.  Hence  almost  all  solutions  rela- 
tive to  analyses,  if  they  require  the  aid  of  heat  and  occupy 
time,  are  most  safely  made  in  flasks.  The  selection  of  a 
basin  or  a  flask  in  any  particular  case  must  be  left  to  the 
judgment  and  experience  of  the  operator. 

381.  In  these  and  similar  cases,  all  sudden  applications 
of  heat,  especially  to  glass  vessels,  should  be  avoided.  A 
glass  flask,  unless  it  be  very  thin,  when  filled  with  a  cold 
fluid,  and  set  suddenly  in  a  hot  sand-bath,  is  almost  sure  to 
break.  It  it  be  required  to  heat  a  basin  in  a  sand-bath,  the 
bottom  should  previously  be  dried,  for  if  wet,  the  water  by 
contact  with  hot  sand  becomes  rapidly  converted  into  va- 
pour, which,  causing  a  slight  explosion,  sometimes  throws 
the  sand  into  the  vessel.  The  elevation  of  temperature  is 
accelerated  by  covering  the  basin  and  preventing  evapora- 
tion. This  is  often  conveniently  done  by  putting  a  second 
basin  somewhat  larger  over  it,  its  cleanliness  having  been 
previously  ensured.  If  the  fire  or  sand-bath  be  such  that  it 
is  advisable  to  obtain  the  heat  as  rapidly  as  possible,  no 
fear  of  injury  being  entertained,  then  on  putting  down  the 
basin  i\  should  not  be  set  upon  the  top  of  the  sand,  or 


PRECAUTION ADDITION  OF  LIQUID.  187 

pressed  down  a  little  way  only,  but  the  sand  should  be  re- 
moved with  the  iron  spatula  before  mentioned  (174)  to  the 
sides,  the  basin  set  down  upon  the  bottom  of  the  bath,  or 
with  only  a  very  thin  layer  of  sand  intervening,  and  then  the 
sand  returned  round  the  sides  of  the  basin.  The  thickness 
of  sand  which  may  be  allowed  to  remain  between  the  bath 
and  the  bottom  of  the  basin,  must  be  left  to  the  judgment 
of  the  experimenter,  being  proportionate  to  the  heat  of  the 
fire  under  the  bath,  the  previous  heat  of  the  sand,  and  the 
quantity  and  nature  of  the  substance  to  be  heated.  It  is  in 
general  advisable  not  to  heap  the  sand  round  the  sides  of 
the  basin  to  a  greater  height  than  the  solution  inside,  at 
least  if  the  sand  be  hot,  or  likely  to  become  so  during  the 
operation;  for  it  then  sometimes  makes  the  part  of  the  dish 
above  the  solution  very  hot,  and  when  ebullition  happens 
and  raises  fluid  over  it,  the  sudden  change  occasions  frac- 
ture, or  gives  rise  to  the  production  of  much  steam,  which 
endangers  the  boiling  over  of  the  contents  of  the  vessel. 

382.  If  it  become  necessary  to  add  water  or  a  cold  liquid 
to  the  contents  of  a  hot  basin  upon  the  sand-bath,  the  addi- 
tions should  be  made  with  great  care,  for  if  the  cold  liquor 
be  poured  at  once  into  the  hot,  it  will  pass  through  it,  and 
striking  against  the  bottom  of  the  hot  basin,  will  very  proba- 
bly break  it.     Hence,  to  avoid  too  sudden  a  change  of  tem- 
perature, the  cold  liquid  should  be  added  slowly,  and  poured 
into  different  parts  of  the  hot  fluid. 

383.  When  a  flask  is  put  upon  the  bath,  it  should  be  sunk 
more  or  less  deep  according  to  the  heat  of  the  sand  and  the 
heat  required,  and  hotter  or  cooler  parts  of  the  bath  may  be 
selected  for  the  same  reasons.     Hence  one  advantage  of  the 
table-furnace  before  described  (169),  whose  sand  baths  pre- 
sent every  required  degree  of  temperature.     If  a  situation 
be  too  hot  for  a  flask,  making  its  contents,  for  instance, 
boil  very  rapidly,  the  heat  is  easily  diminished   by  raising 
up  the  flask  more  or  less,  and  allowing  the  sand  to  sink 
under  it;  this  not  only  causes  a  thicker  stratum  of  sand  to 
intervene  between  the  bottom  of  the  bath  and  the  flask,  but 
also  removes  a  part  of  the  flask  out  of  the  sand  altogether. 

384.  When  a  flask  on  the  bath  is  to  have  its  contents 


188  TIN-CONE RETORT  STAND TRIPOD. 

heated  as  rapidly  as  possible,  it  is  frequently  safer,  instead  of 
endeavouring  to  apply  a  stronger  heat  at  the  bottom  to  pre- 
vent dissipation  of  heat  above.  This  is  very  usefully  effected 
by  a  tin  cone  about  seven  inches  in  diameter  at  its  base,  six 
inches  high,  and  having  a  hole  where  the  apex  would  other- 
wise be,  about  an  inch  in  diameter,  through  which  the  neck 
of  the  flask  may  pass.  This  case  slipped  over  the  flask, 
and  resting  at  its  lower  edge  on  the  sand, 
forms  a  hot  chamber  round  the  upper 
part ;  the  air  within  it  actually  assists  at 
times  to  heat  the  flask  and  its  contents, 
and  in  all  cases  materially  interferes  to 
prevent  cooling.  Even  the  space  left  open  round  the  neck 
may  be  closed  when  desirable,  by  passing  a  piece  of  card, 
with  a  hole  cut  in  it,  over  the  neck,  that  it  may  rest  on  the 
upper  edge  of  the  cone. 

385.  When  a  flask  in  a  state  of  ebullition  on  the  bath 
seems  on  a  sudden  in  danger  of  boiling  over,  it  should  in- 
stantly be  lifted  up  if  possible,  but  at  the  same  time  the  ope- 
rator should  blow  with  his  mouth  against  that  part  of  its  sur- 
face which  is  above  the  level  of  the  fluid.     This  will  gene- 
rally cause  condensation  of  the  steam  within,  the  ebullition 
will  diminish,  and  the  contents  be  secured.     An  expedient 
of  this  kind  will  often  save  the  contents  of  a  flask  when  the 
neck,  from  being  full  of  froth,  is  too  hot  to  be  touched  by 
the  hand;  upon  its  descent  the  neck  will  become  cool,  and 
may  be  laid  hold  of.    When  flasks  are  upon  the  sand-bath, 
a  list  ring  or  two  (68)  should  be  on  one  side,  ready  for  the 
reception  of  the  flask  in  case  of  emergency. 

386.  When  a  small  charcoal  fire  or  a  lamp  is  the  source 
of  heat,  the  basin  or  flask  has  to  be  supported  above  it. 
This  may  be  done  either  by  a  ring-tripod,  or  by  what  are 
called  retort-stands.     With  the  tripod  the  height  is  fixed, 
and  hence  the  lamp  or  furnace  may  require  elevating.     For 
this  and  numerous  other  purposes  of  adjustment  in  the  labo- 
ratory, the  wooden  blocks  before  described  (20)  are  conti- 
nually of  use.     Retort-stands  are  sold  by  the  instrument- 
makers,  and  consist  of  an  upright  brass  rod  fixed  on  a  heavy 
turned  foot,  and  furnished  with  rings,  which  being  each  fixed 


CONSTRUCTION  OF  RETORT-STANDS.          189 

to  an  arm,  and  that  to  asocket,  the  latter  passes  freely  up  and 
down  upon  the  brass  rod,  and  is  made  tight  at  any  particu- 
lar height  by  a  screw-nut  at  the  back  (448.  465)*.  In  this 
way  the  facility  is  obtained  of  fixing  the  projecting  rings  at 
any  height  required,  and  as  several  of  different  sizes  accom- 
pany each  retort-stand,  vessels  with  globular  bottoms,  or  in- 
deed of  many  other  forms,  may  be  supported  at  any  required 
height.  It  is  easy  by  these  stands  to  support  the  flasks  or 
basins  at  the  proper  distance  above  the  lamp  or  furnace. 
When,  from  the  weight  of  the  vessel  and  its  contents,  it  is 
too  heavy  for  the  arm,  or  would  cause  the  stand  itself  to  tip 
over,  then  two  stands  may  be  used  on  opposite  sides,  the  ring 
of  one  being  placed  under  the  other,  and  the  flask  or  basin 
on  the  uppermost.  These  stands  are  generally  made  with 
small  circular  brass  feet,  filled  with  lead,  but  which  still  are 
insufficient  to  retain  the  whole  upright  when  a  heavy  vessel 
is  on  the  ring.  It  is  much  better  to  make  the  foot  of  a  piece 
of  stout  board,  about  twelve  inches  in 
length,  six  inches  in  width,  and  an  inch 
thick.  The  upright  rod  should  be  fixed 
about  one  inch  and  a  half  from  one  end 
of  it,  the  lamp  or  furnace  should  be  placed 
upon  it,  and  the  ring  of  course  in  a  cor- 
responding direction.  Such  an  arrange- 
ment is  perfectly  steady,  and  cannot  be 
overset  by  any  weight  which  it  is  strong 
enough  to  bear.  When  the  usual  stands  only  are  at  hand, 
it  may  now  and  then  be  necessary  to  put  on  a  second  ring 
in  an  opposite  direction  to  the  first,  and  to  add  weights  for 
the  purpose  of  equipoising  the  whole. 

387.  When  a  flask  will  not  fit  very  well,  it  may  be  hung 
up  above  the  lamp  flame  by  a  cord,  for  which  the  common 
shape  of  the  neck  is  well  adapted  :  this  arrangement  may 
often,  on  other  accounts,  be  desirablef- 

*  See  addition  to  paragraph  211.— ED. 

t  Dr  Hare  uses  wire  gauze  to  support  retorts  and  flasks  over  a  fire  or  lamp. 
Its  properties  as  an  obstructor  of  flame  and  a  distributor  of  heat  fit  it  for  special 
usefulness. — ED. 


190  CRUCIBLE  FURNACE — TIN-CONE. 

388.  When  a  crucible  furnace  is  used  it  should  always  be 
placed  on  a  tile,  and  not  immediately  upon  the  wooden  ta- 
ble or  stand,  lest,  during  a  long  operation,  it  should  become 
heated  to  the  bottom  and  burn  the  wood  beneath  (1357). 
The  tile  also  catches  hot  falling  ashes  or  sparks,  which  would 
burn  the  wood,  and  it  facilitates  the  removal  of  the  furnace 
in  the  hottest  state  without  inconvenience.     A  lamp  requires 
no  precautions  of  this  kind.     When  operating  with  flasks 
and  retort-stands,  care  should  Be  taken  that  a  flask,  which, 
with  its  contents,  has  been  heated,  be  not  suddenly  put  upon 
a  cold  ring,  and  that  a  cold  flask  just  charged  be  not  placed 
over  the  fire  upon  a  hot  ring ;  in  both  cases  the  bottoms  of 
the  flasks  will  probably  come  out,  and  the  contents  be  lost. 

389.  When  it  is  desired  to  keep  a  flask  with  its  contents 
in  a  state  of  ebullition  over  a  lamp,  it  may  generally  be  ef- 
fected by  adjusting  the  flame.     But  a  facility  is  gained  by 
having  the  heat  somewhat  greater  than  is  sufficient  when  the 
lamp  is  under  the  centre  of  the  flask,  and  'adjusting  the  ef- 
fect by  moving  the  lamp  a  little  on  one  side.     The  applica- 
tion of  the  heat  is  smaller  or  greater  in  proportion  as  the 
lamp  is  removed  from  the  centre ;  but  at  the  same  time, 
being  applied  on  one  side,  a  cooling  process  goes  on  more 
decidedly  at  the  other  than  before ;  and  this,  with  the  uni- 
formity of  the  current  established  within,  makes  the  whole 
operation  more  regular. 

390.  If  the  effect  obtained  by  a  lamp  is  hardly  sufficient, 
and  yet  from  circumstances  is  the  most  desirable  source  of 
heat,  the  tin  cone  (384)  is  then  a  very  essential   adjunct. 
When  slipped  over,  and  allowed  to  rest  upon  the  flask,  it 
confines  an  atmosphere  of  very  hot  air  about  the  upper  part, 
by  which  the  time  of  heating  is  shortened,  and  in  many  cases 
it  assists  in  the  attainment  of  a  temperature  which  could  not 
otherwise  be   acquired.     The  cone  should  be  guarded  at 
the  upper  part  within  either  by  a  layer  of  thick  paper,  thin 
paste-board,  or  some  such  substance*  or  by  a  ring  of  cork,  to 
prevent  the  metal  from  touching  the  glass  ;  a  circumstance 
which  might  now  and  then,  from  difference  of  temperature, 
produce  fractures.     The  exterior  should  be  preserved  clean 
and  bright. 


SOLUTION — HOOD.  191 

391 .  In  many  cases  of  solution,  the  vapours  emitted,  either 
from  their  acid  nature  or  noxious  qualities,  are  highly  inju- 
rious ;  wherefore  it  is  desirable,  as  much  as  possible,  to  convey 
them  away,  and  to  prevent  their  mixture  with  the  atmosphere 
of  the  place.     Hence  the  use  of  the  large  hood  before  refer- 
red to  (10),  which,  receiving  such  vapours,  conducts  them 
into  the  flue.     A  hood  to  be  useful  should  descend  low,  and 
as  closely  as  possible  over  the  place  from  whence  fumes  are 
to  be  carried  off,  but  this  necessity  often  makes  a  large  hood 
inconvenient.     To  be  effectual,  it  should  also  have  a  good 
draught  passing  through  it. 

392.  A  temporary  moveable  hood  is  a  useful  appendage 

to  the  table-furnace  before  described  (169). 
It  consists  of  a  cone  having  its  lower  diame- 
ter equal  to  that  of  the  round  sand-bath 
(171),  supported  on  three  short  legs  to  rest 
within  the  edge  of  the  bath,  and  opening 
above  into  a  funnel-pipe,  which,  by  three 
bends  at  right  angles,  is  made  to  terminate 
opposite  the  fire  door.  The  pipe  is  conveni- 
ently formed,  in  two  or  three  pieces,  the  whole  being  of  cop- 
per ;  the  cone  itself,  and  the  pipe  and  joint  above,  may  be 
made  of  copper,  or  very  advantageously  of  stone-ware. 
When  placed  upon  the  sand-bath,  with  the  door  of  the  fire 
partly  open,  and  the  end  of  the  pipe  opposite  the  aper- 
ture, such  a  draught  is  occasioned  through  the  whole  as  will 
carry  off  any  fumes  which  may  be  liberated  beneath  it  into 
the  chimney. 

393.  The  inside  of  a  hood  of  this  kind  should  be  kept 
clean,  to  prevent  the  possibility  of  dirt  falling  from  it  into  the 
vessels  beneath.     When  the  vessel  is  a  flask,  an  additional 
security  is  obtained  by  covering  the  mouth  loosely,  either  by 
inverting  over  it  a  short  tube,  closed  at  one  end,  and  suffi- 
ciently large,  or  by  placing  upon  it  a  convex  fragment  of  old 
glass  from  a  retort  or  flask.     When  the  vessel  is  a  basin,  it 
may,  in  some  cases,  be  similarly  guarded  by  another  basin, 
placed  over  it  as  before-mentioned  (274) ;  when  that  cannot 
be  done,  the  cleanliness  of  the  hood  should  be  particularly 
attended  to. 


192  SOLUTION — PRECAUTIONS. 

394.  When  the  contents  of  a  flask  evolve  vapour  spontane- 
ously, or  require  but  little  heat  to  produce  them,  the  flask 
may  be  placed  upon  a  listed  ring  (68),  in  an  inclined  posi- 
tion, and  have  its  mouth  directed  to  the  ash-pit  of  the  fur- 
nace :  the  draught  will  carry  away  the  fumes  whilst  it  is  in 
that  position,  and,  at  intervals,  it  may  be  placed  for  a  few 
minutes  together  on  the  sand-bath.     Where  the  spare  flues 
exist,  which  have  been  before  referred  to  (5,  168),  they  are 
very  useful  in  carrying  off  vapour.    The  mouth  of  a  flask 
brought  near  to  one  will  deliver  all  its  vapours  into  the  flue, 
and  from  the  height  of  the  latter,  it  is  easy  to  arrange  the 
flask,  with  its  lamp  or  furnace,  in  a  proper  position.     When 
the  portable  hood,  just  referred  to  (392,  168),  is  adapted  to 
the  aperture  of  the  flue,  which  may  easily  be  effected  when 
the  pipe,  as  mentioned,  is  in  two  or  three  shifting  pieces,  no- 
thing more  can  be  desired ;  for,  so  arranged,  a  good  flue  is 
competent  to  carry  off  all  the  fumes  from  any  basin  which 
the  hood  can  cover.     Where  the  table-furnace  is  favourably 
situated,  as  against  the  side  of  the  laboratory,  no  difficulty 
occurs  in  using  a  piece  of  pipe,  which  may  be  put  up  in  a 
moment,  and  connect  a  moveable  hood  over  any  part  of  the 
sand-bath,  with  the  flues  behind. 

395.  Besides  these  general  directions  for  the  process  of 
solution,  there  are  numerous  precautions  requisite  to  ensure 
accuracy,  when  results  of  the  utmost  precision  are  required, 
as  in  cases  of  analysis ;  amongst  which  are  the  following. 
If  the  quantity  of  solid   matter  operated  upon  has  been 
weighed,  it  is  of  consequence  that  not  a  particle  be  lost  in 
introducing  it  into  the  flask,  supposing  such  a  vessel  to  be 
used.    The  experimenter  should  not  venture  to  pour  it  into 
the  neck  directly  from  the  glazed  paper  in  which  it  may  have 
been  weighed  (61),  or  from  any  vessel  that  may  contain  it, 
but  should  use  a  small  clean  funnel  for  the  purpose.     If  dry, 
the  powder  will  probably  pass  freely  through  it,  without  ad- 
hering to  the  glass;  but  before  removing  the  funnel,  it  should 
be  washed  with  a  little  water,  which  will  carry  down  any 
adhering  particles.     If,  in  passing  through  the  funnel,  some 
of  the  powder  has  struck  against  and  adhered  to  the  inside 
of  the  neck  of  the  flask,  that  should  also  be  washed  down  to 


EFFERVESCENCE ROD-POURING.  193 

the  bottom  with  a  little  water.  The  water  which  is  used  for 
these  purposes  should  be  distilled,  and  indeed  in  all  cases 
'  where  accuracy  is  required,  equal  care  should  be  taken  on 
that  point.  It  is  much  to  be  regretted  that  any  laboratory 
should  be  so  far  restricted  in  the  use  of  distilled  water  as  not 
to  have  sufficient  for  every  case  of  solution,  whether  for  refi- 
ned analyses  or  the  most  ordinary  experimental  process  (26). 

396.  When  effervescence  happens  in  the  flask,  precau- 
tions should  be  taken  that  none  of  the  solution  be  lost. 
During  a  cold  effervescence,  as  of  carbonate  of  lime  in  an 
acid,  the  breaking  of  the  bubbles  will  throw  up  a  shower  of 
particles,  many  of  which  will  ascend  several  inches  perpen- 
dicularly.    In  these  cases,  it  will  be   right  to  incline  the 
flask  at  an  angle  of  about  45°,  for  then  the  rising  drops  will 
meet  with  and  break  against  the  side  of  the  flask,  and  be 
retained.     At  other  times,  when  strong  currents  of  vapour  or 
gas  are  produced  at  the  same  time  with  this  dispersion  from 
the  breaking  of  bubbles,  many  of  the  particles  may  be  car- 
ried away  by  the  current,  even  when  the  flask  or  vessel  may 
be  considerably  inclined.     In  these  cases,  the  addition  of 
the  acid,  or  the  application  of  heat,  should  be  made  cau- 
tiously, that  the  current  may  not  become  so  rapid,  and  at- 
tain such  power  as  to  do  harm.     For  the  same  reason,  ope- 
rations which    are  liable  to  occasion  much  effervescence 
should  be  performed  in  flasks  of  the  largest  size,  that  the 
current  of  gas  within  may  have  less  velocity,  and  that  the 
particles  may  have  room  and  time  to  fall. 

397.  On  pouring  solutions  from  glasses,  flasks,  or  basins 
in  the  ordinary  way,  it  is  scarcely  possible  to  operate,  so 
that,  on  ceasing  to  pour,  and  returning  the  vessel  to  its  first 
position,  a  small  portion  of  the  liquid  shall  not  flow  down 
the  outside ;  or  if  successfully  done  once,  there  is  no  cer- 
tainty  that  it  can  be  performed  whenever  required       A 
failure  of  this  kind  occasions  a  loss  of  substance,  which, 
when  repeated,  is  quite  incompatible  with  the  accuracy  of 
analytical  processes ;  but  it  may  be  avoided  by  very  simple 
means.     A  clean  glass  rod  (374)  is  to  be  dipped  into  the 
solution  to  be  poured,  so  as  to  have  its  surface  at  the  end 

Z 


194  ROD  SUBSTITUTED  FOR  A  FUNNEL. 

wetted,  and  then,  the  vessel  being  inclined,  the  rod  is  to  be 
applied  in  a  vertical  or  highly  inclined  position,  so  that  its 
wet  surface  shall  touch  the  lip  or  edge  from  which  it  is  in- 
tended to  pour.  When,  by  further  motion  of 
the  vessel,  the  fluid  at  last  runs  over  its  edge, 
it  will  proceed  down  the  rod,  being  conducted 
by  it  in  any  required  direction.  When  a  suffi- 
cient quantity  has  in  this  way  been  removed, 
the  vessel  is  to  be  restored-  to  its  first  position, 
the  rod  not  being  withdrawn  until  the  fluid  is 
decidedly  below  the  inside  edge;  all  that  is 
without  will  be  confined  to  the  surface  of  the 
rod,  not  a  particle  having  flowed  down  the  out- 
side of  the  basin.  The  rod  may  be  left  in  the 
solution  until  a  fresh  portion  is  to  be  poured ; 
or  if  no  more  be  required,  may  be  washed  by  a  little  water 
from  the  dropping  bottle  (402),  which,  being  added  to  the 
original  solution,  prevents  the  loss  of  a  single  particle  of  the 
contained  substance. 

398.  This  application  of  the  rod  is  not  merely  useful  in 
preventing  loss  or  waste,  but  also  in  conducting  the  fluid  in 
particular  directions,  when  other  means  are  wanting.     A  so- 
lution, or  liquid  of  any  kind,  which  wets  the  rod,  may  be 
poured  very  accurately  and  securely  into  a  narrow-mouthed 
bottle  by  it,  if  a  funnel  be  not  at  hand,  and  occasionally  it 
even  surpasses  the  funnel  in  convenience.     Thus  in  pouring 
successive  small  quantities  of  a  valuable  fluid,  a  rod  enables 
it  to  be  done  safely,  and  at  the  same  time  with  considerable 
minuteness,  by  allowing  a  very  small  stream  to  flow  from  its 
end,  the  vessel  being  in  contact  with  the  rod,  but  a  little  way 
above  it;  between  each  operation  of  pouring,  the  rod  is  con- 
veniently and  securely  placed  in  the  fluid.     With  a  funnel, 
a  much  larger  surface  is  moistened,  which  drains  for  some 
time  after,  and  the  quantity  is  by  no  means  so  well  estimated 
as  by  the  former  method  :  neither  in  the  intervals  of  pouring 
can  the  funnel  be  so  conveniently  disposed  of  as  the  rod. 

399.  If  upon  any  sudden  emergency  the  pouring  has  to 
be  performed   without  the  guiding  rod,  and  yet  loss  of  the 


POURING  OUT  MINUTE  QUANTITIES.  195 

substance  would  be  of  consequence,  then  put  the  lip  from 
which  the  fluid  is  to  flow,  against  the  further  side  of  the 
mouth  of  the  vessel  which  is  to  Deceive,  inclining  the  latter 
if  necessary  at  the  time. 

400.  The  operations  which  have  been  described  have  fre- 
quently to  be   performed   on   a  very  minute  scale  (915). 
Hence  the  use  of  small  earthenware  dishes,  platinum  capsules, 
and  especially  fragments  of  broken  flasks  (371),  which,  from 
their  concave  form,  are  exceedingly  convenient  for  experi- 
ments upon  drops  of  fluids.     In  operations  of  this  kind,  heat 
is  applied,  either  by  a  small  spirit-lamp  flame,  obtained  by 
pulling  down  the  cotton  before  the  lamp  is  lighted,  or  by 
touching  the  glass  with  the  hot  sand  of  the  bath,  or  even 
by  letting  it  stand  upon  the  hotter  part  of  the  furnace  plate. 
Instead  of  flasks,  tubes  are  used  in  similar  operations  for  mak- 
ing minute  solutions,  the  general  management  of  which  will 
be  described  in  Sect.  xvi.  (917). 

401.  Instead  of  pouring  out  the  fluid,  it  has  now  to  be 
transferred  in  portions,  each  less  than  a  drop,  and  this  is  best 
done  by  dipping  a  glass  rod  into  the  solution,  and  then, 
whilst  more  or  less  adheres  to  it,  according  to  the  quantity 
wanted,  to  touch  a  clean  glass  plate  or  a  piece  of  flask  with 
it,  and  allowing  the  adhering  portion  to  run  down.     If  but 
little  be  required,  only  a  small  length  of  the  rod  should  be 
dipped  in,  and  if  still  less  be  required,  even  that  small  por- 
tion should  be  allowed  to  drain  for  a  moment  or  two,  before 
the  rod  is  brought  into  contact  with  the  substance  to  be 
moistened.     On  the  contrary,  if  a  large  quantity  be  wanted, 
two  or  three  inches  of  the  rod  should  be  dipped  in,  and  the 
adhering  fluid  quickly  transferred  to  the  desired  place;  or  if 
the  most  be  wanted  that  the  rod  can  lift,  it  should,  upon  be- 
ing dipped,  be  taken  out  horizontally,  and  carried  adroitly 
in  that  position  to  the  place  required,  taking  care,  by  slight 
but  proper  motions  of  the  rod,  to  prevent  such  accumulation 
of  the  fluid  in  one  spot  as  to  cause  a  drop.     By  these  means, 
a  glass  rod  may  be  made  to  carry  very  different  quantities 
of  fluid,  affording  great  facilities  in  the  practice  of  minute 
chemistry. 

402.  There  is  an  instrument  which  cannot  be  dispensed 


196         COMMON  DROPPING  BOTTLE HARE5S. 

with  in  the  laboratory,  and  which,  in  the  order  of  our  ar- 
rangement, first  comes  into  service  in  the  present  chapter — 
it  is  the  dropping-bottle.  4ts  use  is  to  supply  small  quan- 
tities of  water,  and  the  laboratory  should  be  furnished  with 
two  of  them,  one  to  deliver  large  and  rapid  drops,  or  a  small 
stream,  the  other  to  supply  very  minute  portions  for  such 
experiments  as  those  just  referred  to.  The  larger  one  may 
be  a  bottle  holding  about  half  a  pint,  and  should  have  a 
good  smoothly  cut  cork  fitted  into  its  mouth.  A  piece  of 
strong  glass  tube,  of  an  internal  diameter  not  more  than  the 
eighth  of  an  inch,  should  be  selected  and  drawn  out  so  as  to 
have  a  contracted  aperture,  which  at  the 
time,  should  be  bent  on  one  side;  the  piece 
of  tube  should  be  about  two  and  a  half  inch- 
es long,  and  fitted  tightly  into  the  cork, 
its  extremity  not  passing  inwards  beyond 
the  cork;  and  it  is  an  advantage  that  the  surface  of  the 
latter  should  be  slightly  concave  or  conical,  as  in  the  accom- 
panying section.  Lastly,  a  notch  is  to  be  cut  in  the  side  of 
the  cork,  diminishing  from  above  downwards,  so  that  when 
the  latter  is  in  its  place,  the  notch  may  form  a  passage  into 
the  bottle,  with  a  narrow  opening  at  the  inner  surface.  This 
slit  is  to  be  on  that  side  of  the  cork  from  which  the  upper 
extremity  of  the  tube  inclines.*. 

403.  The  bottle  is  to  have  distilled  water  put  into  it,  and 
being  then  placed  in  different  positions,  it  will  supply  a 
stream  of  water  variable  in  its  quantity  at  pleasure.  If  in- 
verted, it  will"  be  found  that  a  small  stream  will  flow  out  at 
the  beak,  and  a  current  of  air  enter  at  the  notch  to  supply 
its  place.  If  the  bottle  be  inclined,  keeping  the  notch  up- 
permost, the  stream  will  not  be  so  rapid,  and  in  consequence 
of  the  diminished  perpendicular  height  of  the  column  of  water 
tending  to  descend,  occasioned  by  bringing  it  nearer  to  a 
horizontal  position,  the  stream  will  at  last  break  into  single 
successive  drops,  which  by  a  still  further  motion  of  the  hand 
also  cease  to  fall.  If  a  small  portion  of  water  be  required 
to  make  a  solution,  it  is  readily  supplied  even  to  single  drops, 

*  A  gum-elastic  bag  with  a  slender  pipe  attached  to  its  mouth  furnishes  a  more 
convenient  dropping  bottle.    See  Hare's  minutes  p.  31.— ED. 


SELECTION  OF  SOLVENTS.  197 

and  smaller  quantities  are  easily  lifted  and  transferred  as  be- 
fore described,  by  a  glass  rod  (401).  Or  if  a  stream  be 
wanted  to  wash  the  solution  from  a  rod  or  a  funnel,  or  to 
wash  out  a  glass,  it  is  instantly  obtained.  By  allowing  the 
stream  or  drops  to  fall  from  a  greater  or  smaller  height,  va- 
riations in  the  descending,  and  consequently  washing  force, 
are  produced;  this  may  even  be  increased  occasionally,  by  a 
downward  jerking  motion  of  the  hand,  which  will  throw  out 
forcible  independent  jets  of  water. 

404.  It  is  proper  to  have  a  smaller  dropping-bottle  ready 
for  use,  because,  from  the  infinite  variety  in  the  quantities 
to  be  operated  upon  by  the  chemist,  such  an  instrument  will 
at  times  be  found  advantageous.     By  making  the  tube  smal- 
ler, a  similar  set  of  capabilities  to  those  just  described,  but 
with  a  smaller  stream  of  water,  are  obtained,  and  a  minute 
quantity  of  a  rare  substance  of  which  it  is  desired  to  save 
every  atom  may  be  operated  with,  yet  without  more  dilution 
than  is  absolutely  necessary. 

405.  The  selection  of  solvents  for  particular  substances  is 
an  important  point,  which  must,  however,  in  a  great  measure 
be  left  to  the  judgment  and  knowledge  of  the  student.     If 
the  object  be  to  ascertain  the  properties  of  a  substance  by 
working  with  its  solutions,  water  should  be  first  tried.     If  it 
have  no  action,  alcohol  may  be  used,  and  after  that  ether, 
pyroligneous  ether,  and  finally,  on  some  occasions,  oils.     As 
a  general  rule,  those  solvents  are  to  be  preferred  which  are 
evaporable,  and  may  therefore  be  dissipated  by  heat,  and 
which  at  the  same  time  least  effect  the  chemical  powers  of 
the  substance  to  be  dissolved.     In  these  properties,  and  in 
economy,  water  surpasses  every  other  body  that  can  be  used. 

406.  Mixtures  of  water  and  alcohol  are  frequently  useful, 
where  neither  water  nor  alcohol  alone  is  applicable.     Thus 
if  muriate  of  soda  and  sulphate  of  lime  were  mixed  together, 
the  muriate  is  best  dissolved  by  water ;  this,  however,  would 
occasion  the  solution  of  a  portion  of  the  sulphate  of  lime, 
whereas  by  a  mixture  of  one  part  of  alcohol  and  two  or  three 
parts  of  water,  a  solvent  is  produced  which  will  separate  the 
former  salt  and  reject  the  latter. 

407.  When  an  aqueous  solution  of  a  vegetable  substance 


198  COMPLEX  VEGETABLE  INFUSION. 

has  been  made,  which  on  examination  is  found  to  contain 
different  substances,  some  soluble  in  alcohol  and  others  not 
(and  there  are  few  infusions  of  vegetables  that  do  not  yield 
such  a  mixture),  it  has  to  be  subjected  to  the  action  of  alco- 
hol for  the  purpose  of  effecting  a  separation.  The  first  step 
is  concentration  by  evaporation ;  but  it  is  advisable  not  to 
carry  this  to  dryness,  or  as  far  as  may  be  without  injury  to 
the  substance,  and  then  to  act  by  alcohol ;  for  generally  a 
soft  mass  is  obtained,  upon  which  alcohol  acts  only  imper- 
fectly, except  in  a  long  period,  because  the  last  portions  of 
soluble  matter  are  protected  by  the  mass  of  insoluble  sub- 
stance. It  is  better  to  suspend  the  evaporation  when  the 
substance  is  a  thick  fluid,  and  then  to  add  a  small  quantity 
of  alcohol ;  which,  although  it  will  cause  a  partial  solution 
and  partial  precipitation  at  first,  will,  upon  being  stirred,  mix 
with  the  fluid,  and  be  over-powered  as  it  were  by  the  water 
still  remaining,  so  that  the  precipitated  portion  will  be  re- 
dissolved,  and  the  whole  again  rendered  fluid.  This  should 
be  repeated  twice  or  thrice,  stirring  each  time,  and  keeping 
the  mixture  of  uniform  consistency ;  a  precipitation  will  gra- 
dually take  place,  increasing  as  the  proportion  of  alcohol  is 
increased.  The  particles  thus  rejected  as  insoluble  will  be 
nearly  free  from  any  mixture  of  substances  soluble  in  the  al- 
cohol, if  at  least  there  be  no  chemical  affinity  interfering, 
and  thus  a  ready  solution  of  the  one  part,  and  its  separation 
from  the  other,  may  be  effected.  The  quantity  of  alcohol 
added  must  be  such  as  at  last  to  surpass  by  many  times  the 
quantity  of  water  left  at  the  close  of  the  evaporation,  other- 
wise its  powers  will  be  diluted,  and  a  complete  separation  of 
that  which  is  soluble  from  that  which  is  insoluble  will  not  be 
obtained.  Hence  the  evaporation  should  be  carried  as  far 
as  possible,  so  that  the  residue  be  fluid  and  will  mix  readily. 
If  it  be  so  thick  that  it  clots  upon  adding  the  first  portion  of 
spirit,  a  few  drops  of  water  must  be  added.  The  solution 
should  be  in  such  a  state  that  the  first  portion  of  alcohol, 
equal  to  about  a  fourth  of  the  bulk,  should  cause  precipita- 
tion, which  disappears  upon  stirring ;  the  second  portion 
cause  a  turbid  liquor  after  stirring ;  the  third,  an  increase  of 
turbidness  but  still  no  clotting ;  the  fourth,  when  an  equal 


SOLVENTS THE  ACIDS.  199 

volume  has  been  used,  a  separation  of  the  precipitable  part 
in  softer  or  harder  masses.  When  three  or  four  times  the 
volume  has  been  added,  it  will  generally  be  found  that  the 
separation  is  complete. 

408.  Some  of  the  acids  frequently  act  as  mere  solvents : 
their  power  apparently  not  being  due  to  any  combination 
effected  between  them  and  the  substance  by  which  a  change 
of  character  is  produced.     Thus  acetic  acid  dissolves  ca- 
outchouc, and  acetic,  nitric,  muriatic,  and  some  other  acids, 
dissolve  phosphates  and  borates.     Muriatic   acid  dissolves 
sulphate  of  lead,  to  a  slight  degree  muriate  of  silver,  and  many 
other  such  actions  will  be  observed  in  the  course  of  experi- 
mental investigations,  all  of  which  should  be  remembered, 
and  may  in  turn  be  put  to  important  uses. 

409.  When  acids  and  other  energetic  chemical  substances 
soluble  in  water  are. used,  either  as  simple  solvents  or  as  pro- 
ducing compounds  by  combination,  attention  should  be  paid 
in  their  selection  to  certain  general  advantages  which  each 
possesses.     Nitric  acid  is  distinguished  as  a  chemical  solvent 
by  the  solubility  of  almost  all  the  salts  which  it  forms  ;  by  its 
imparting  oxygen  to  metals  generally,  so  as  to  bring  them 
into  a  soluble  state ;  and  by  its  ready  separation  from  all  its 
compounds  at  a  sufficiently  high  temperature, —  three  cir- 
cumstances of  very  great  importance.     When  used,  care 
should  be  taken   that  it  is  sufficiently  diluted  :  very  strong 
nitric  acid  will  sometimes  seem  to  have  no  power  over  a  body 
at  common  temperatures,  when  upon  the  addition  of  a  little 
wate^  action  will  immediately  commence.     This  circum- 
stance never  occurs  with  acid  which  has  been  diluted  with 
one  half  its  bulk  of  water.    Any  further  dilution,  therefore, 
can  only  be  required  to  moderate  chemical  action,  and  not 
to  commence  it.     Muriatic  acid  yields  salts  generally  solu- 
ble, though  some  of  them  are  but  slightly  so  ;  and  muriate  of 
silver  not  at  all  so  in  water.     Many  of  the  resulting  com- 
pounds are  fixed  at  a  red  heat,  some  few  sublime,  some  are 
decomposed.     The  muriatic  acid  has  the  advantage  of  be- 
ing separable  from  the  bodies  it  has  combined  with  by  solu- 
tions of  silver.     Sulphuric  acid  forms  many  insoluble  salts 
but  it  has  the  advantage  of  being  removed  readily  by  solu- 


200  SOLVENTS ALKALIES INFLUENCING  CAUSES. 

tions  of  barytic  salts.  The  circumstance  of  its  producing  in- 
soluble salts  makes  it  valuable  as  a  chemical  solvent  for  those 
bodies  with  which  it  combines  and  remains  in  solution,  inas- 
much as  it  facilitates  their  separation  from  the  others.  Hence 
it  is  frequently  added  to  solutions  made  by  muriatic  and  ni- 
tric acids,  and  displacing  these,  they  are  afterwards  separa- 
ted by  heat.  It  should  not  be  used  in  its  concentrated  state, 
but  more  or  less  diluted,  or  the  same  effect  will  occur  as 
with  nitric  acid.  Acetic  acid  forms  soluble  salts  with  all  the 
substances  with  which  it  combines ;  and  it  may  be  burnt  off 
by  heat,  with  access  of  air. 

410.  When  an  alkaline  solvent  is  required,  ammonia,  if  ef- 
fectual, is  most  convenient,  because  of  its  ready  volatility  and 
dissipation  when  uncombined,  and  the  volatility  of  all  its  or- 
dinary salts,  except  the  phosphate,  borate,  and  those  contain- 
ing metallic  acids.     When  ineffectual,  the  fixed  alkalies  must 
be  resorted  to. 

411.  It  is  necessary  that  the  student  be  on  his  guard  re- 
specting certain  variations  in  the  solubility  of  bodies  arising 
from  the  presence  of  other  matters.     He  will  continually  find 
that  small  portions  of  substances  generally  considered  as  in- 
soluble in  water  will  remain  in  neutral  solutions  when  some 
other  substance  is  present,  or  because  of  slight  mutual  de- 
composition ;  and  he  will  also  frequently  find  that  matter, 
usually  considered  as  readily  soluble,  is  so  with  difficulty 
when  in  contact  with  substances  with  which  it  is  not  appa- 
rently in  combination.     Thus  water  boiled  upon  muriate  of 
potash  and  phosphate  of  baryta  will  be  found  to  contaiDimore 
baryta  than  if  boiled  alone  upon  the  phosphate;  and  on  the 
contrary,  if  oxide  of  iron  and  alumina  be  precipitated  to- 
gether from  a  solution,  it  will  be  found  much  more  difficult  to 
dissolve  the  alumina  by  solution  of  potash  than  if  it  had  been 
thrown  down  alone. 

412.  The  alkaline  earths  are  remarkably  soluble  in  solu- 
tions of  sugar,  and  also,  though  to  a  less  degree,  in  solutions 
of  extract  and  other  vegetable  matters  :  hence  they  are  re- 
tained in  solution  at  times  in  very  unexpected  situations,  and 
might  give  rise  to  much  uncertainty  in  the  appearances  and 
characters  of  other  substances,  unless  the  experimenter  were 


SOLVENTS VARIATIONS.  201 

aware  of  the  general  fact.  Platinum  is  not  itself  soluble  in 
nitric  acid,  even  when  spongy,  and  in  its  most  comminuted 
form,  but  when  alloyed  in  small  quantities  with  metals  dis- 
solved by  that  acid,  it  becomes  soluble  with  them,  and,  in 
consequence,  appears  now  and  then  in  situations  where  it  is 
not  expected. 

413.  Tartaric  acid  or  tartrates  have  an  extraordinary  pow- 
er of  rendering  many  metallic  oxides  soluble,  which  are  not 
so  by  other  acids  without  it;  and  still  more  in  holding  them 
in  solution  when  such  substances  are  added  as  in  ordinary 
circumstances  effect  their  separation.     The  oxides  of  bis- 
muth, antimony,  tin,  and  titanium,  are  easily  dissolved  by 
acids  when  tartaric  acid  is  present ;  and  being  present,  am- 
monia no  longer  has  the  power,  upon  its  addition,  of  separa- 
ting the  oxides  of  iron,  titanium,  manganese,  cerium,  cobalt, 
nickel,  lead,  antimony,  and  the  earths,  alumina,  magnesia, 
and  yttria,  from  their  solutions,   and,  in  certain  cases,  even 
potash  or  soda  fail  so  to  do.     Great  advantage  may  be  taken 
of  this  property  occasionally,  but  sometimes  it  is  equally  dis- 
advantageous in  preventing  the  usual  action  of  re-agents*. 

414.  A  very  numerous  class  of  aqueous  solutions  is  pro- 
duced by  metallic  salts.     These,  in  consequence  of  the  va- 
ried quantity  of  oxygen  with  which  many  of  the  metals  can 
combine,  are  susceptible  of  changes  dependent  upon  the 
oxygenation  of  the  metal  whilst  the  state  of  solution  is  con- 
tinued.   These  changes  are  eminently  useful  in  fitting  the 
solutions  in  one  way  or  another  for  experimental  purposes. 
If  the  object  be  to  oxidize  the  metal,  whether  to  render  it 
soluble,  or  for  any  other  purpose,  the  agents  to  be  employed 
are  the  acids  generally,  nitric  and  nitromuriatic  acids  espe- 
cially, chlorine  and  chlorate  of  potash,  and,  in  some  peculiar 
cases,  even  alkalies.     No  metal  will  dissolve  in  water  or  an 
acid  until  it  is  combined  with  oxygen,  and,  in  obedience  to 
this  law,  sulphuric  and  phosphoric  acids,  and  perhaps  muri- 
atic acid,  frequently  cause  the  decomposition  of  water  for 
the  oxygenation  of  the  metal.     Nitric  acid  is  often  decom- 
posed, supplying  a  portion  of  its  own  oxygen  to  the  metal 
with  which  it  is  in  contact.     Proto-salts  in  solution  are  fre- 

*  Annales  de  Chimie,  xxiii.  356. 

2  A 


202  METALLIC  SOLUTIONS. 

quently  converted  into  per-salts  by  it,  and  also  by  nitro-mu- 
riatic  acid  and  chlorine,  A  proto-sulphate,  muriate, or  nitrate 
of  iron,  may  be  converted  into  a  per-salt  by  a  little  nitric  or  ni- 
tro-muriatic  acid  and  heat;  and  a  proto-nitrate  by  heat  alone. 
The  same  agents  are  equally  effectual  in  converting  proto- 
salts  of  tin  into  per-salts.  In  these  cases  of  conversion  care 
should  be  taken  that  no  acid  be  added  that  will  interfere 
with  the  future  experiments,  or  that  may  not  be  dissipated 
by  heat. 

415.  The  influence  of  alkali  in  causing  oxygenation  may 
be  observed  by  putting  a  little  oxide  of  chrome  or  a  salt  of 
chromium  into  a  solution  of  alkali,  so  that  the  latter  may  be 
in  excess;  by  evaporation  to  dryness  in  a  platina   capsule, 
and  heating  the  mixture  with  access  of  air,  the  oxide  of 
chrome  will  absorb  oxygen,  and  become  chromic  acid,  through 
the  influence  of  the  alkali,  with  which  it  will  ultimately  com- 
bine. 

416.  If  deoxidizing  agents  be  required   for  the  metal  in 
solution,  then  an  efficient  one  is  most  likely  to  be  found 
amongst  such  bodies  as  alcohol,  ether,  sugar,  gum,  &c.     Of 
the  known  metals,  per-salts  of  manganese  are  reduced  to  the 
state  of  proto-salts  by  being  boiled  with  alcohol  or  ether,  and 
become  quite  colourless :  solutions  of  platinum  and  palladium 
are  actually  reduced  by  boiling  with  alcohol.     The  per-ox- 
ides  of  lead  and  manganese,  when  mixed  with  any  of  the 
bodies  enumerated  and  an  acid,  are  reduced  to  the  state  of 
protoxides,  and  dissolved  if  the  acid  be  such  as  to  form  solu- 
ble salts.     If  a  chromate  have  excess  of  acid  added  to  it, 
with  a  little  of  any  of  the  same  substances,  and  be  heated,  it 
loses  oxygen  and  becomes  oxide  of  chrome,  which,  with  the 
excess  of  acid,  forms  a  salt.     These  facts  are  mentioned  ge- 
nerally rather  than  particularly,  that  being  combined  with 
the  pupil's  previous  knowledge,  they  may  assist  him  in  sur- 
mounting a  difficulty,  and  in  devising  the  most  expedient  pro- 
cess by  which  he  may  attain  his  objects.     The  processes  of 
analysis  and  research  require  to  be  so  infinitely  varied  un- 
der different  circumstances,  that  every  possible  action  and 
every  practicable  expedient  is  necessarily  resorted  to  in  turn 
to  enable  the  experimenter  to  proceed. 


SOLUTION  OF  ORGANIC  MATTEll.  203 

417.  The  general  principles  and  directions  given  with  re 
spect  to  the  solution  of  inorganic  matter,  will  apply  to  a  great 
extent  to  that  of  organic  substances.     The  few  differences 
that  occur  depend  upon  the  situation  of  the  matter  to  be  dis- 
solved, and  upon  its  destructible  nature.     The   active  prin- 
ciples to  be  separated  are  generally  in  small  quantity  com- 
pared to  that  of  the  inert  enveloping  substance,  and  the  lat- 
ter is  often  easily  affected  by  powerful  agents,  such  as  acids 
and  alkalies,  and  converted  into  bodies  which,  though  use- 
less, are  soluble,  and  would  contaminate  the  solution.     Hence 
it  is  necessary  to  select  such  agents  as,  at  the  same  time  that 
they  act  with  energy  on  the  principles  to  be  dissolved,  have 
no  power  over  the  accompanying  matter.     Acids  and   alka- 
lies are  therefore  objectionable.     Indeed  a  still  more  cogent 
reason  exists  for  their  rejection  in  general,  namely,  a  reaction 
upon,  and  destruction  of,  the  peculiar  principles  themselves. 
Hence  a  frequent  recurrence  to  such  solvents  as  water,  alco- 
hol, and  ether,  either  cold,  or  aided  by  heat;  and  if  acids  or 
alkalies  are  used,  they  should  be  diluted  and  applied  only 
after  the  other  solvents  have  exhausted  their  powers,  or  for 
the  separation  of  known  principles  to  which   their  action  is 
favourable. 

418.  M.  Robinet   has  lately  recommended  the  use  of 
neutral  saline  solutions  in  particular  cases*,  stating  that  a 
separation  of  known  principles  may  be  sometimes   effected 
by  them,  where  water  dissolves  the  whole  or  acts  only  im- 
perfectly. 

419.  The  original  vegetable  or  animal  substance,  if  dry, 
may  be  rasped  or  bruised  (333, 357),  so  as  to  be  divided  into 
small  pieces,  but  not  generally  into  powder.     If  the  action 
required  be  but  short,  hot  water  poured  over  the  substance  in 
a  basin  may  be  sufficient:  but  if  a  longer  time  be  required, 
the  mixture  must  be  retained  in  a  sand-bath,  or  over  a  lamp, 
as  before.     When  hot  water  is  merely  poured  upon  the  sub- 
stance, the  process  is  named  Infusion.  When  the  heat  is  con- 
tinued for  some  time  by  the  application  of  fire,  Decoction;  and 
when  it  consists  of  pouring  cold  or  warm  water  on  the  sub- 

*  Anuales  de  Cliimie,  xxx.  208. 


204  LIXIVIATION. 

stance,  and  allowing  it  to  stand  for  some  time,  it  is  called 
Maceration. 

420.  A  very  excellent  and  useful  process  of  solution  is 
called  Lixiviation.  It  is  applicable  only  to  such  substances 
as,  from  their  porous  nature,  are  permeable  to  water,  and 
consists  in  the  separation  of  a  soluble  body  from  an  insolu- 
ble one  by  washing.  For  this  purpose  the  mixture  is  to  be 
loosely  arranged,  and  water  added  till  it  fills  all  the  cavities, 
and  covers  the  surface  of  the  mass.  In  the  laboratory  it  may 
be  conveniently  performed  in  the  small  way  in  a  funnel, 
and  shall,  therefore,  be  so  described.  Suppose  it  were  ne- 
cessary to  wash  the  salts  from  a  quantity  of  ashes:  a  funnel 
of  sufficient  size  should  have  the  lower  aperture  stopped  by 
a  cork,  and  should  be  supported  on  a  stand,  so  that  it  may 
steadily  retain  its  proper  position.  A  few  pieces  of  the  ash, 
of  such  size  that  they  shall  .not  pass  through  the  neck  of  the 
funnel,  should  be  introduced  in  the  first  place,  to  prevent  the 
descent  of  the  matter  to  be  placed  over  it.  Having  added 
pieces  rather  smaller,  until  the  surface  exposed  in  the  funnel 
is  an  inch  in  diameter,  the  rest  should  be  crushed  in  a  mor- 
tar to  a  coarse  powder,  or  rather  to  small  pieces  or  grains, 
and  put  into  the  funnel  above  that  previously  arranged.  If 
the  substance  be  such  that  it  will  not  afford  lumps  of  suffi- 
cient size  or  strength  to  remain  in  the  neck  of  the  funnel  and 
support  the  rest,  then  its  place  should  be  supplied  by  some 
pieces  of  broken  glass,  which  may  be  continued  to  the  height 
before  mentioned,  and  which,  while  they  support  the  sub- 
stance, afford  abundant  passages  for  the  fluid  when  required. 
Being  thus  far  arranged,  hot  or  cold  water  is  to  be  poured 
into  the  funnel  according  to  circumstances,  its  quantity  be- 
ing such  that  it  will  just  cover  the  mass.  The  whole  is  to 
be  left  in  that  state  for  a  time  proportionate  to  the  solubility 
of  the  substances  present.  The  water  which  has  penetrated 
the  fragments  will  gradually  dissolve  the  salts,  and  forming 
a  heavy  solution,  will  descend  in  the  free  spaces,  changing 
situations  with  the  water  not  yet  saturated.  In  this  way  a 
solution  will  be  produced  of  much  greater  strength  below 
than  above,  and  the  upper  part  of  the  mass  will  be  washed 
almost  perfectly  at  the  first  operation.  When  sufficient  time 


DISTILLATION.  205 

has  been  allowed,  according  to  the  quantity  and  nature  of 
the  salt,  and  the  manner  in  which  it  is  enveloped,  the  cork 
beneath  should  be  withdrawn,  and  one-half  or  two-thirds  of 
the  solution  suffered  to  run  out  gradually,  not  hastily,  lest 
greater  disturbance  of  the  solid  matter  in  the  funnel  be  oc- 
casioned than  is  necessary  or  advantageous.  The  cork  is  to 
be  replaced,  fresh  water  added  above,  so  as  not  to  disturb 
the  arrangement :  and  being  left  as  before  for  a  time,  the 
second  solution  should  then  be  withdrawn,  and  this  opera- 
tion repeated  till  the  water  which  passes  is  perfectly  free 
from  salts,  or  contains  so  little  as  to  make  further  attention 
unnecessary. 

421.  As  before  remarked,  this  operation  can  only  be  per- 
formed on  such  substances  as  permit  access  of  water  to  all 
parts.  When  the  particles  fall  together,  or  adhere  slightly, 
and  so  prevent  contact  of  the  water,  and  choke  up  the  chan- 
nels, then  recourse  is  sometimes  had  to  the  intermixture  of 
inert  matter,  as  hay,  straw,  coarse  sand,  or  broken  glass;  but 
it  is  better  in  such  cases,  when  they  occur  in  the  laboratory, 
to  put  the  substance  into  a  basin  or  glass  with  excess  of  water, 
and  by  agitation  every  now  and  then,  effect  the  solution  in 
the  usual  way. 


SECTION  VII. 
DISTILLATION— SUBLIMATION. 

422.  DISTILLATION  and  sublimation  have  the  same  object, 
and  require  nearly  the  same  means  ;  both  consist  in  the  con- 
version of  a  body  into  vapour,  its  transference  in  that  state, 
and  consequent  separation  from  other  substances,  and  its 
ultimate  condensation.  The  difference  generally  consists  in 
the  state  assumed  by  the  vapours  when  condensed ;  if  the 
product  be  solid,  the  process  is  called  sublimation;  if  liquid, 
distillation.  All  that  is  recfuired  is,  that  the  substance  to  be 
distilled  or  sublimed  should  be  raised  to  such  a  temperature, 


206  DISTILLATION COMMON  STILL. 

that  it  will  assume  the  gaseous  form,  and  in  this  form  con- 
ducted into  a  receptacle  of  such  temperature,  as  to  cause  its 
resumption  of  the  fluid  or  solid  state. 

423.  Simple  as  is  the  process  in  theory,  there  are  few  that 
are  liable  to  greater  variety  of  arrangement.     The  range  of 
temperatures  at  which  different  bodies  rise  in  yapour  is  very 
extensive;  for  sulphurous  acid  or  chlorine  assumes  that  state 
at  temperatures  below  the  freezing  point  of  water,  whilst 
mercury  or  zinc  require  one  verging  upon,  or  even  surpass- 
ing, a  red  heat.     Thus,  on  the  one  hand,  very  low  tempera- 
tures, are  required  to  effect  condensation,  and,  on  the  other, 
very  high  ones  to  cause  the  requisite  vaporization.     The  ves- 
sels and  the  apparatus  to  be  employed  must  not  only  be  adap- 
ted to  these  points,  but  also  effectually  to  meet  the  innume- 
rable varieties  in  the  quality  and  quantity  of  the  substances 
operated  upon  (924). 

424.  The  common  still  will  serve  best  to  exemplify  the  or- 
dinary points  requiring  attention  in  the  process  of  distillation. 
It  may  be  used  both  for  water  and  alcohol,  and  if  the  labo- 
ratory be  not  otherwise  supplied  with  .distilled  water,  must 
continually  be  had  recourse  to  for  that  necessary  article  (26). 
The  still  consists  of  a  metal  boiler  to  contain  the  water  to  be 
purified ;  to  this  is  adapted  a  head,  which  terminates  in  a 
beak,  and  the  latter  is  made  to  fit  into  the  commencement  of 
a  spiral  tube  called  the  worm,  fixed  in  a  tub,  the  whole  of 
this  part  being  called  the  refrigerator.     The  process  consists 
in  raising  the  water  into  vapour  in  the  still,  and  condensing 
that  vapour  in  the  worm  ;  the  condensed  water  runs  out,  and 
is  received  at  the  lower  extremity,  which  ought,  in  all  cases, 
to  be  left  open. 

425.  It  will  be  necessary  to  preserve  a  sufficient  fire  under 
the  boiler  during  the  distillation,  not  merely  to  produce  ebul- 
lition, but  also  to  cause  the  water  to  boil  rapidly,  so  as  to  af- 
ford a  quick  succession  of  vapour,  otherwise  the  operation 
will  be  very  tedious.     It  is  important ,M-u  all  cases,  to  keep 
the  top  of  the- still  hot,  or  the  vapours  will  condense  there, 
and,  flowing  down  the  sides  to  the  water  below,  will  be  again 
vaporized,  and  cause  great  waste  of  heat.     For  this  reason  it 
is  useful,  when  the  top  is  exposed  to  the  air,  to  cover  it  with 


DISTILLATION USE  OP  THE  STILL.  207 

a  dry  cloth,  this  precaution  being  continued  to  the  descend- 
ing part  of  the  beak  or  pipe.  It  is  also  necessary  to  observe 
that  this  pipe  be  sufficiently  capacious  for  the  passage  of  the 
steam  to  the  condenser  without  any  obstruction  :  every  thing 
in  this  part  of  the  apparatus  should  be  arranged  so  as  to  ge- 
nerate vapour  with  great  rapidity,  and  to  convey  it  with  cor- 
responding readiness  to  the  worm.  The  student  must  not 
forget  that  as  the  water  is  distilled,  itsquantity  will  diminish 
in  the  vessel,  and  should  be  replenished  before  any  injury 
arises  from  its  deficiency.  • 

426.  The  vapour  having  reached  the  worm  is  there  to  be 
condensed  ;  and  therefore  the  worm  is  put  into  a  tub,  and 
surrounded  with  cold  water,  the  low  temperature  of  which 
causes  the  substance  to  lose  its  elastic  form,  and  flow  out  in 
the  liquid  state.     From  the  quantity  of  heat  communicated 
to  the  refrigerating  water,  which  is  greater  as  the  operation 
is  more  successfully  carried  on,  it  will  become  necessary  to 
change  it  readily  and  quickly,  and  many  contrivances  have 
been  resorted  to  for  this  purpose,  amongst  the  best  of  which 
are  those  that  supply  a  constant  stream  of  cold  water  to  the 
bottom  of  the  tub,  and  draw  off  an  equal  quantity  of  hot  from 
the  top.     Whatever  the  arrangements  are,  the  water  must 
never  be  allowed  to  become  hot,  or  if  it  does  so  at  the  sur- 
face, it  should  be  but  moderately  warm  at  two  or  three  in- 
ches beneath  ;  for,  although  in  some  cases  it  may  happen, 
that  when  the  upper  half  of  the  water  is  hot,  the  lower  half 
may  still  be  sufficient  to  condense  the  steam,  yet  inconveni- 
ences  often  arise.     Amongst  these  is  occasionally  one  of 
more  consequence  than  mere  failure  of  condensation  ;  thjs  is, 
the  obstruction  occasioned  to  the  passage  of  the  steam,  when 
it  has  to  force  its  way  uncondensed  through  several  coils  of 
small  hot  pipe,  and  which,  at  times,  may  become  so  great  as 
even  to  cause  the  forcing  up  of  the  head  of  the  still.     As  be- 
fore mentioned,  any  obstruction  to  the  free  liberation  and 
condensation  of  the  steam  interferes  with  the  effectual  work- 
ing of  the  still,  and  causes  a  consequent  loss  of  heat  and 
expense  of  fuel. 

427.  The  water  which  flows  out  at  the  end  of  the  worm 
should  never  be  more  than  warm.     It  may  be  received  and 


DISTILLATION RETORTS. 

preserved  in  stone  bottles,  and  should  always  be  tested,  that 
its  purity  may  be  known.  The  end  of  the  worm  should  not 
usually  be  allowed  to  dip  into  water,  so  as  to  close  the  aper- 
ture, as  in  that  case,  from  irregularities  in  the  liberation  of 
steam,  much  agitation  is  now  and  then  produced ;  and,  at  a 
moment  of  inattention,  the  water  which  has  been  distilled 
may  actually  return  back  into  the  boiler,  from  a  partial  con- 
densation therein. 

428.  The  vessels,  in  which  most  laboratory  distillations 
are  effected,  are  retorts  (16)  and  flasks  (372).     Retorts  are 
of  every  size  and  shape,  and  of  very  various  materials  ;  those 
made  of  glass  are  equal  to  all  operations  which  may  be  con- 
ducted at  temperatures  less  than  that  at  which  the  glass  sof- 
tens, and  by  luting  may  be  used  at  much  higher.    They  admit 
of  constant  observation  of  the  materials  within,  are  acted  upon 
or  injured  by  very  few  substances,  and  may  be  cleaned,  ge- 
nerally, with  facility.     Their  great  point  of  failure  is  that  of 
brittleness,  which   endangers  both   the  apparatus   and  its 
contents. 

429.  With  regard  to  the  general  form  of  glass  retorts,  it 
is  not  of  any  very  great  consequence,  as  respects  their  use  in 
distillation  and  sublimation  :  they  will  be  required  with  necks 
of  very  different  lengths  and  dimensions,  and  with  bodies  of 
various  proportion  as  relates  to  the  necks  ;  the  general  propor- 
tions may  be  nearly  those  of  the  accompanying  figure.     But 

^  the  case  is  different  when  they  are 

\  intended   for  exhaustion,  as    in  nu- 

c  ~~^  merous  pneumatic  experiments  (866); 

for  having  then  the  pressure  of  the 
atmosphere  to  support  on  their  ex- 
terior  surface,  their  form  should  be 
carefully  attended  to.  Retorts  that  are  carelessly  bent  in 
the  making  are  liable  to  two  imperfections  of  form,  which 
frequently  weaken  them  so  much  as  to  render  them  unable 
to  bear  exhaustion  ;  the  one  is  a  flattening  of  the  convex  sur- 
face at  a,  and  the  other  is  a  sharp*  fold  or  double  in  the 
glass  at  the  opposite  part  6,  which  expands  the  two  sides 
(at  c),  so  that  a  section  made  through  those  parts  would 
have  a  resemblance  to  a  long  flat  ellipsis.  Such  a  shaped 


RETORTS TUBULATED.  209 


retort  will  barely  bear  the  pressure  of  the  atmosphere  on 
the  flattened  parts,  but  will  crack  during  exhaustion  at  c  and 
the  opposite  corresponding  side,  or  will  be  shattered  and 
crushed  to  pieces.  Retorts  should  therefore  be  generally 
chosen  sufficiently  convex  in  all  parts,  the  degree  of  curva- 
ture of  one  part  passing  gradually  into  that  of  the  neigh- 
bouring portions,  as  is  represented  in  the  figure.  Such  a 
retort,  though  very  thin,  will  bear  exhaustion  with  perfect 
safety  ;  and  that  a  sufficient  number  may  be  on  the  shelves 
when  required,  let  all  be  selected  with  a  view  to  such  an 
application. 

430.  With  regard  to  thickness,  retorts  should  be  exam- 
ined as  directed  for  glass  flasks  (372);  the  bulb  should  be 
uniform,  or  nearly  so,  throughout :  if  there  be  any  difference, 
the  part  at  d  should  be  thinnest,  gradually  thickening  to  the 
neck.  All  should  be  rejected  of  which  the  part  at  d  is 
thicker  than  elsewhere,  the  application  of  heat  being  almost 
sure  to  break  them.  The  general  thickness  should  be  that 
of  flasks  of  about  the  same  capacity,  except  that  small  retorts 
are  better  rather  thicker  in  proportion  to  their  size,  or  even 
occasionally  as  thick  as  the  large  ones,  because  they  are  more 
frequently  subjected  to  temperature  at  which  glass  becomes 
soft.  All  retorts  with  spots  or  grains  of  sand  in  the  part  to 
be  heated  should  be  rejected  ;  they  are  liable  to  fly  at  those 
places. 

431.  The  size  of  retorts,  on  the  shelves,  should  vary,  in 
the  capacity  of  their  bulbs,  from  two  ounces  to  two  pints. 
A  few  large  ones  may  be  at  hand,  on  a  by-shelf,  for  parti- 
cular uses. 

432.  Retorts  are  either  tubulated  or  plain.     When  tubu- 
lated (465)  they  are  more  likely  to  crack,  from  the  irregu- 
larity of  form  and  thickness  of  glass  at  the  juncture,  than 
when  plain;  but,  being  very  convenient  in  particular  cases, 
by  allowing  easy  access  to  the  interior  of  the  retort,  some 
will  be  required.     The  aperture  should  be  in  such  a  posi- 
tion as  to  open  into  the  body  of  the  retort  freely,  admitting 
a  funnel  or  a  rod  into  it  without  interfering  with  the  neck, 
and  yet  as  little  beyond  the  curve  where  the  neck  commen- 
ces as  possible.     The  tubulature  is  safest,  when  it  is  not  much 

2  B 


210  RETORTS — STOPPERS. 

thicker  than  the  retort  at  the  part  where  they  join,  but  should 
.thicken  upwards,  and  be  sufficiently  strong  to  admit  of 
having  a  glass  stopper  ground  into  it  in  a  tight  and  secure 
manner.  When  the  tubulatures  are  put  on  like  a  thick  knot 
of  glass,  they  soon  break  off,  and  the  retort  is  of  course 
destroyed. 

433.  In  all  cases  where  ground-glass  stoppers  are  used, 
and  they  are  very  numerous,  though  this  of  the  tubulated 
retort  is  the  first  we  have  arrived  at,  they  should  be  ex- 
amined, and  the  accuracy  of  the  grinding  ascertained. 
They  should  be  so  ground  as  not  to  be  liable  to  fix  and 
become  immoveable,  and  be  so  accurate  as  to  remain  air- 
tight for  months,  and  even  for  years,  when  a  little  pomatum, 
or,  rather,  hard  tallow  is  put  round  them.  A  stopper  should 
be  slightly  conical,  so  that,  when  introduced,  it  may  at  once 
obtain  its  place,  and  bear  on  every  part  of  the  ground 
surface.  Being  moved  round  in  its  situation,  it  should  feel 
perfectly  steady  and  firm  in  the  aperture,  in  every  part  of 
the  revolution ;  and  more  accurately  to  prove  the  regularity 
in  the  hole  and  stopper,  by  which  they  come  in  contact  in 
all  parts,  the  stopper  should  be  pressed  sideways  in  different 
directions,  and  in  different  parts  of  the  revolution,  to  find 
out,  if  possible,  any  one  position  in  which  it  shakes  a  little 
in  its  place  ; — none  such  ought  to  occur.  This  ascertained, 
a  little  tallow  should  be  put  upon  the  stopper,  both  that  and 
the  aperture  being  clean  and  dry,  and  being  then  again  in- 
troduced and  turned  round,  a  film  of  the  tallow  will  inter- 
vene between  the  two  surfaces  of  glass,  which,  at  the  same 
time  that  it  occasions  perfect  freedom  of  motion  in  the  stop- 
per as  regards  its  turning  round  in  the  hole,  does  not  at  all 
render  it  less  firm  and  steady  in  its  bearing  than  before ;  and 
it  perfectly  closes  the  passage,  so  that  no  portion  of  liquid 
or  of  gas  can  pass  between  them.  If  a  stopper  is  not  tight, 
it  is  easily  rendered  so  by  grinding  (1230). 

434.  Finally,  with  reference  to  the  state  of  the  retort,  it 
should  be  observed,  that  no  retort,  when  once  cracked  in 
any  part  near  the  bulb,  should  be  used  in  cases  where  heat 
has  to  be  applied  to  liquid  contents.  Their  use  must  then 


CHARGING  RETORTS.  211 

be  confined  to  cold  operations,  or  to  sublimations  in  unim- 
portant experiments. 

435.  A  student  has  many  points  to  attend  to  relative  to 
the  charging  of  retorts,  or  the  method  of  introducing  sub- 
stances into  them.  If  a  substance  in  the  state  of  lumps  or  of 
powder  is  to  be  put  into  a  plain  retort,  and  it  is  required 
that  the  neck  be  preserved  in  a  clean  state,  the  best  prepa- 
ratory step  is  to  insure  the  cleanness  and  dryness  of  the  re- 
tort (1251,  1252),  so  that  no  portion  of  the  substance  shall 
have  any  tendency  to  adhere  to  the  glass.  If  it  be  a  powder, 
it  should  fall  down  one  side  of  the  neck;  being  introduced, 
if  there  be  occasion,  by  a  small  clean  funnel  (395).  It  should 
not  be  thrown  down  in  a  careless  way,  while  the  neck  is  held 
in  a  perpendicular  position  :  by  holding  the  retort  in  an  in- 
clined position,  the  powder  is  less  separated,  and  adheres  less 
to  any  part  of  the  internal  surface.  If  it  be  in  lumps,  they 
should  be  made  to  slide  down  one  by  one,  the  neck  being 
inclined  at  an  angle  of  40°  or  45°.  If  held  more  upright,  or 
the  pieces  be  heavy,  there  is  a  probability  of  their  passing 
through  the  retort  by  their  momentum.  The  retort  must  not 
be  held  with  the  bottom  of  the  bulb  downwards,  for  then  the 
pieces  as  they  pass  from  the  neck  will  fall  suddenly  upon, 
and  almost  certainly  break  it ;  but  it  must  be  turned  halfway 
round,  so  that  as  the  piece  descends  it  may  pass  over  that 
part  which,  when  the  retort  is  in  its  right  position,  forms  its 
internal  upper  surface.  In  this  manner  masses  of  metal  and 
other  heavy  substances  may  be  introduced  without  endanger- 
ing the  vessel.  When  the  retort  is  tubulated,  precautions 
relative  to  keeping  the  neck  dry  and  clean  are  not  so  neces- 
sary, because  there  is  no  occasion  for  soiling  it.  The  powder 
may  be  introduced  by  a  funnel  as  before,  and  even  washed 
in  with  a  little  water  (395) ;  and  masses  may  be  introduced 
also  at  the  tubulature,  not  dropping  them,  but  allowing  them 
to  slide  in  safely. 

436.  No  instruction  is  necessary  for  the  introduction  of 
liquid,  if  a  little  waste,  or  the  soiling  of  the  vessel,  be  un- 
important points ;  but  when  either  of  these  is  of  conse- 
quence, the  student  should  be  acquainted  with  the  methods 
of  avoiding  them.  If  the  neck  is  to  be  preserved  clean,  as 


212  DISTILLATION RETORTS. 

is  often  the  case  when  acids  are  introduced,  the  end  is  easily 
obtained  with  the  tubulated  retort,  by  the  use  of  a  funnel 
with  a  beak  so  narrow  and  long,  that  it  may  pass  into  the 
body  of  the  vessel.  A  few  moments  should  be  allowed  for 
the  funnel  to  drain,  and  it  should  at  last  be  drawn  out  adroitly 
immediately  after  a  drop  has  fallen,  and  before  another  is 
ready  to  descend ;  and  during  its  removal  the  wet  beak 
should  be  held  so  steadily  as  not  to  touch  the  side  of  the 
tubulature. 

437.  If  the  retort  be  not  tubulated,  then  a  funnel  with  a 
long  narrow  beak,  sufficient  to  pass  down  the  neck  of  the 
retort,  and  to  reach  the  bulb  at  the  end,  must  be  used ;  or 
if  such  a  funnel  be  not  at  hand,  and  the  case  is  imperative, 
a  piece  of  glass  tube,  rather  longer  than  the  neck,  may  be 
employed  for  the  purpose,  the  fluid  being  carefully  poured 
down  the  interior  of  the  tube.     In  using  the  long-necked 
funnel  or  the  tube,  care  should  be  taken  that  the  end  does  not 
dip  into  the  fluid  already  in  the  retort,  for  the  exterior  should 
be  preserved  clean  and  dry,  that  its  removal  may  be  effected 
without  soiling  the  neck.     For  this  purpose,  when  the  funnel 
or  tube  has  drained  a  few  moments,  it  should  be  inclined 
with  the  retort,  until  the  neck  is  nearly  in  a  horizontal  posi- 
tion, or  even  has  passed  it  a  little  ;  that  which  was  the  lower 
end  will  now  be  the  upper ;  and  the  fluid,  still  adhering  to 
the  inner  surface,  instead  of  flowing  as  before  to  the  extre- 
mity, and  gathering  there  in  a  drop,  will  tend  to  return  upon 
its  former  course,  leaving  the  end  almost  dry.     In  this  state 
the  tube  or  funnel  may  easily  be  withdrawn  from  the  retort, 
without  any  risk  of  soiling  it,  if  its  extremity  be  prevented 
from  touching  the  glass ;  for  no  further  dropping  can  take 
place. 

438.  The  size  of  a  retort  must  be  regulated  by  the  quan- 
tity of  substance  to  be  used,  and  by  the  kind  of  action  ex- 
pected to  occur.     If  the  contents  be  fluid  or  semi-fluid,  and 
the  liberation  of  gas  or  ebullition  be  expected,  the  charge 
should  not  occupy  more  than  one-half  or  one-third  the  capa- 
city of  the  bulb ;  or  if  the  action  be  likely  to  be  rapid,  not 
so  much  :  but  if  no  expansion  or  swelling  take  place,  nor  any 
commotion  by  which  particles  may  be  thrown  over ;  or  if,  in 


HEATING  RETORTS.  213 

other  cases,  although  portions  are  liable  to  be  thrown  into 
the  neck,  it  be  desirable  to  act  on  as  much  of  the  substance 
introduced  as  possible,  the  charge  may  then  occupy  much 
more  of  the  body  of  the  retort. 

439.  The  general  methods  of  applying  heat  to  glass  retorts 
is  the  same  with  those  adopted  for  heating  flasks  (381,  &c.); 
and  the  spirit-lamp  (199,  201),  hot  air  (269),  water/steam, 
and  sand-baths  (258,  271,  381,  176),  oil-lamps  (212,  386), 
and  small  crucible  furnaces  (386),  may  all  be  used  in  turn, 
with  the  precautions  before  given.     Sometimes  a  little  vari- 
ation is  required,  dependent  upon  the  following  circumstan- 
ces.    In  certain  forms  of  distillation  the    heat  is  applied 
merely  to  excite  and  increase  chemical  action ;  this  is  the 
case  in  the  production  of  several  gases  from  mixed  materials; 
and  in  such  cases,  when  the  temperature  has  attained  the 
necessary  point,  the  application  of  heat  must  be  diminished, 
until  it  is  merely  sufficient  to  preserve  the  temperature  al- 
ready acquired.     In  other  cases  a  greater  resemblance  exists 
to  the  process  of  distillation  already  described  (424),  and  it 
is  required  not  merely  to  allow  a  certain  temperature,  but  to 

communicate  heat  for  some  time  with 
more  or  less  rapidity,  that  the  liquid 
in  the  retort  may  be  converted  into 
vapour,  and  carried  over.  Hence  the 
necessity  of  a  command  over  the  fire, 
so  that  it  may  be  increased  or  dimin- 
ished at  pleasure. 

440.  The  oil-lamp  is  of  great  service  in  chemical  distilla- 
tions, from  its  ready  management,  but  sometimes  scarcely 
yields  heat  enough  for  the  performance  of  quick  operations. 
In  such  cases  the  upper  part  of  the  retort  should  be  covered, 
to  prevent  its  being  cooled  by  contact  of  the  air,  and  this  can 
often  be  effectually  done  by  a  thick  paper  or  card-board 
cone,  with  a  broad  notch  to  admit  the  neck ;  this  interferes 
with  a  ready  change  of  the  air  at  the  top  of  the  retort,  and 
saves  much  heat,  which  would  otherwise  escape  at  that  part 
from  the  condensation  of  the  vapour  within*. 

A  very  quick  heat  is  producible  by  the  blow-pipe  vertical  flame  (211).— ED. 


214  EVOLUTION  OF  VAPOUR  FACILITATED. 

441.  The  evolution  of  vapour  is  in  many  cases  very  much 
facilitated  by  the  addition  of  substances  having  apparently 
no  chemical  action ;  and  the  process  of  distillation  is  not 
only  thus  promoted,  but  rendered  possible  and    easy,  in 
cases  where  otherwise  it  would  be  almost  unattainable.     If 
diluted  alcohol,  spirits  of  wine,  wine,  or  certain  alcoholic 
solutions  be  distilled  in  glass  vessels,  the  vapour  is  frequently 
evolved   with  difficulty  ;  the  contents  of  the  retort  at  one 
moment  not  boiling  at  all,  and  at  another  bursting  through- 
out into  a  mass  of  vapour  and  fluid,  which  fills  the  whole 
body  of  the  vessel.     This  endangers  the  sudden  expulsion 
of  part  of  the  substance,  causing  serious  derangement  of  the 
process,  and  is  also  accompanied  with  such  agitation  of  the 
fluid,  such  bumping  and  shaking  of  the  retort,  as  at  times 
actually  to  endanger  the  safety  of  the  whole  :  for  when  the 
vapour  is  formed,  it  is  with  such  force  as  to  produce  a  dull 
explosion.    This  is  prevented  by  the  introduction  of  a  few 
angular  or  fragmented  pieces  of  solid  matter  into  the  retort, 
of  such  nature  as  not  to  be  acted  upon  by  any  of  the  sub- 
stances present.     For  this  purpose  metallic  substances  are 
the  best ;  a  piece  of  platinum  foil  cut  by  scissors  into  narrow 
slips,  so  as  to  resemble  a  fringe,  or  seven  or  eight  inches  of 
silver,  platinum,  or  copper  wire  pressed  up  loosely,  or  plati- 
num and  silver  filings — are  then  very  useful.     So  also  is  a 
fragment  of  cork  or  a  piece  of  torn  cartridge  paper,  any  of 
which  will  generally  cause  the  regular  and  tranquil  evolu- 
tion of  vapour,  and  occasion  the  distillation  to  proceed  qui- 
etly and  satisfactorily. 

442.  The  same  effect  takes  place  with  sulphuric  acid 
when  distilled  in  glass  vessels,  but,  from  the  weight  of  the 
fluid  and  the  high  temperature  employed,  with  more  force 
and  more  danger  to  the  retort.     In  this  case  the  ill  conse- 
quences which  would  result  from  the  fracture  of  the  vessel 
are  much  increased  by  the  highly  corrosive  power  of  the 
substance  at  exalted  temperatures.     If,  however,  a  piece  of 
platinum  foil  be  introduced  into  the  retort,  the  operation 
proceeds  quietly,  the  vapour  rises  readily,  and,  with  the  ex- 
ception of  the  high  heat  necessary,  the  distillation  goes  on 
as  freely  as  that  of  water. 


WIRE  INTRODUCED CAUTION.  215 

443.  The  student  should  be  cautioned  against  the  sudden 
introduction  of  these  promoters  of  vaporization,  whilst  the 
fluids  are  hot.  if,  upon  the  occurrence  of  bumping  during 
a  distillation  of  alcohol,  sulphuric  acid,  or  any  other  fluid, 
in  glass  vessels,  a  piece  of  any  one  of  the  substances  men- 
tioned were  suddenly  introduced  by  the  tubulature,  it  is 
probable  that  the  consequent  burst  of  vapour  would  be  so 
instantaneous  and  strong  as  to  do  more  harm  than  the 
bumping  itself.  The  safer  method  is  to  remove  the  source 
of  heat  for  a  moment,  then,  opening  the  tubulature,  to  in- 
troduce a  platinum  wire,  letting  it  touch  only  the  surface  of 
the  fluid  at  first,  and  introducing  more  of  it  as  the  ebullition 
occasioned  by  it  ceases ;  when  that  is  over,  the  wire  should 
be  withdrawn,  the  cork,  the  platinum,  or  whatever,  accor- 
ding to  the  nature  of  the  fluid  within,  has  been  selected,  be 
introduced,  the  stopper  closed,  heat  applied,  and  the  distil- 
lation proceeded  with. 

444.  The  effect  of  these  promoters  is  best  observed  upon 
sulphuric  acid.     If  two  or  three  measured  ounces  of  strong 
sulphuric  acid  be  put  into  a  clean  glass  flask  and  heated 
over  a  small  charcoal   fire,  as  soon  as  the  acid  begins  to 
boil,  it  will  exhibit  the  irregularity  described.     The  foil  is 
then  to  be  dropped  in,  and  its  power  of  forming  vapour  will 
be  sufficiently  visible.     Sulphuric  acid  will  boil  several  de- 
grees lower  in  a  glass  vessel  containing  a  piece  of  foil,  than 
in  one  not  so  assisted.     Professor  Oersted  has  stated,  that 
the  introduction  of  brass  wire  into  brandy  very  much  accele- 
rates   the  process  of   distillation*;    and  Dr  Bostock  has 
noticed  similar  effects  with  regard  to  etherf.     For  these 
and  other  facts  I  must  refer  to  the  authority  quoted  beneath. 

445.  The  products  evolved  in  distillatory  operations  may 
be   considered  generally  as  of  two  kinds  ;    vaporous,    or 
such  as  may  be  condensed  at  ordinary  pressure  by  the  low 
temperatures  we  can  commapd  ;  and  gaseous,  or  such  as 
resist  these  means,  and  hence  have  been  called  permanent- 
ly elastic.     Since  the  general  relation  of  gases  and  vapours 
to  each  other  has  been  distinctly  explained  and  confirmed 

*  Annals  of  Philosophy,  New  Series,  ix,  157,  f  Ibid,  ix,  196. 


# 
216  DISTILLATION RECEIVER. 

by  experiment,  this  division  is  known  to  be  very  unscien- 
tific, but  it  is  convenient  in  operations,  and,  being  generally 
retained  in  chemical  language,  there  can  be  no  objection 
to  it  in  this  place.  The  operations  of  distillation  here  verge 
upon  pneumatic  manipulation  ;  but  as,  in  consequence  of  the 
peculiar  means  required  for  the  retention  and  transference 
of  that  form  of  matter,  all  processes  relative  to  gases  will  be 
more  conveniently  considered  together,  the  further  direc- 
tions in  this  chapter  will  be  confined  entirely  to  such  ope- 
rations as  relate  to  condensable  substances. 

446.  Retorts  being  used  for  the  purpose  of  raising  sub- 
stances into  vapour,  receivers  become  necessary  for  their 
condensation.     Receivers  are  vessels  which  perform  a  cool- 
ing as  well  as  a  retaining  office,  and  are  as  variable  in  their 
kinds    as   retorts.     Sometimes  a  simple  tube  is  used,  at 
others  flasks,  globes,  and  bottles;  these  receive  the  vapours, 
condense  them,  and  retain  the  resulting  fluid.     On  other 
occasions  the  receiving  apparatus  is  more  complicated  in 
form ;  one  part  serving  to  condense  the  vapours,  and  anoth- 
er to  contain  the  products.     These  varieties  and  the  me- 
thods of  managing  them  will  be  best  illustrated  by  exam- 
ples. 

447.  The  simplest  arrangement  of  retort  and  receiver  is 
to  introduce  the  beak  of  the  former,  when  charged,  into  the 
mouth  of  the  latter,  which  may  be  a  flask  or  globe  (372), 
and  then  proceed  to  distil.     This  is  an  arrangement  readily 
made,  and  in  constant  use  in  experiments  upon  inexact 
quantities.     The  receiver  is  frequently  retained  sufficiently 
cold  by  the  air  to  condense  the  vapours ;  or,  if  it  be  desira- 
ble to  increase  the  refrigerating  power,  it  may  easily  be  done 
by  putting  the  globe  into  a  basin  of  cold  water.     During 
the  distillation  the  globe  may  be  turned  now  and  then,  to 
bring  different  parts  into  contact  with  the  water  in  the  basin; 
and  if  at  times  it  becomes  quickly  heated  from  a  rapid  pro- 
duction of  vapour,  the  cooling  power  may  be  increased  by 
covering  the  upper  surface  with  a  doubled  piece  of  filtering 
paper,  and  pouring  a  little  water,  at  intervals,  over  it.     Wa- 
ter, and  most  substances  not  less  volatile  than  it,  may  in  this 
way  be  distilled  in  ordinary  experiments,  with  very  little 


DISTILLATION CONDENSATION. 


217 


loss.  Nevertheless,  as  the  vessels  are  open,  and  the  cool- 
ing process  is  not  fitted  for  the  condensation  of  a  sudden  or 
large  production  of  vapour,  the  arrangement  should  not  be 
used  except  in  experiments  in  which  the  substances  re- 
maining in  the  retort  are  the  same  with  those  which  are 
condensed,  or  where  a  little  loss  of  matter  is  of  no  conse- 
quence. 

448.  On  other  occasions,  although  an  open  apparatus  may 
be  convenient  or  necessary  for  the  ready  substitution  of  one 
receiver  for  another,  yet  great  cooling  power  may  be  re- 
quired.    An  arrangement  requisite  for  the  distillation  of  sul- 
phurous acid  will  illustrate  some  of  the  means  which,  either 
separately  or  in  conjunction,  are  then  advantageously  appli- 
cable.    The  retort  in  which  the  sulphurous  acid  is  generat- 
ed is  attached,  by  a  caoutchouc  connecter  (840),  with  a 

bent  piece  of  glass  tube  of  the 
form  represented  in  the  figure, 
and  that  again  by  another  caout- 
chouc connecter,  with  a  second 
bent  tube,  also  figured  in  the 
cut.  The  first  tube  is  to  be 
placed  in  a  glass  or  other  vessel, 
convenient  for  holding  a  frigo- 
rific  mixture  (454-) ;  the  second  is  for  the  purpose  of  con- 
ducting the  gas  into  the  receiver,  and  is  represented  as  pass- 
ing into  a  small  stoppered  flask.  These  tubes  should  be  of 
sufficient  diameter  to  allow  of  the  free  passage  of  all  the  gas 
that  may  be  liberated,  and  the  first  or  cooling  tube  should 
be  so  large  as  also  to  retain  all  the  fluid  that  may  be  con- 
densed there,  and  yet  allow  free  passage  for  the  uncondensed 
gas. 

449.  The  caoutchouc  or  India-rubber  connecting  pieces  are 
easily  made,  and  are  of  such  constant  use  in  attaching  tubes 
and  apparatus  for  the  conveyance  of  vapours  and  gases,  that 
a  number  of  them,  from  an  inch  to  two  inches  long,  and  from 
a  quarter  to  half  an  inch  in  diameter,  should  be  kept  ready  in 
a  box  or  drawer  ( 1 122).     They  are  most  easily  made  of  the 

2C 


218  CAOUTCHOUC  CONNECTERS. 

sheet  caoutchouc,  prepared  by  Mr  Hancock*,  which  is  about 
the  tenth  or  twelfth  of  an  inch  thick,  and  may  be  had  in 
pieces  ten  or  twelve  inches  square.  A  piece  of  this  caout- 
chouc, about  an  inch  and  a  half  square,  is  to  be  slightly 
warmed  till  it  becomes  flexible  and  soft,  and  then  put  round 
a  glass  rod  or  other  cylindrical  body,  rather  smaller  than 
the  intended  tube  ;  the  projecting  edges  are  to  be  pinched 
together,  and  when  they  have  slightly  adhered,  cut  through 
with  a  pair  of  very  sharp,  clean  scissors;  this  will  remove 
the  superfluous  caoutchouc,  will  expose  perfectly  clean 
surfaces  upon  each  edge,  and  leave  the  two  edges  slightly 
adhering  together.  The  junction  is  to  be  completed  by  im- 
mediately bringing  these  edges  into  contact  throughout  the 
whole  extent  of  cut  surface ;  which  may  be  done  by  apply- 
ing a  thumb-nail  upon  each  side  the  section,  and  pressing 
the  surfaces  together,  the  glass  rod  within  supporting  the 
caoutchouc,  and  thus  assisting  to  obtain  the  desired  adhe- 
sion. This  operation,  if  neatly  performed,  will  cause  the 
cut  surfaces  to  apply  so  accurately  to  each  other,  that  no 
part  of  either  will  appear.  When  firmly  pressed  together 
whilst  warm,  the  adhesion  is  such  that  the  tube  will  tear 
elsewhere  as  readily  as  at  the  junction.  The  tube  should 
be  made  so  loose  that  it  will  easily  slip  off*  the  glass  rod. 
If  the  caoutchouc  has  been  stretched  to  make  the  edges 
meet,  and  the  tube  consequently  fits  closely  to  the  rod,  it 
will  frequently  adhere  so  tightly  as  to  be  difficult  of  re- 
moval; but  this  may  be  obviated  either  by  putting  a  little 
flour  over  that  surface  of  the  caoutchouc  which  is  to  be  the 
inside  of  the  tube,  and  which  prevents  its  adhesion  to  the 
glass;  or  by  wrapping  a  piece  of  paper  first  round  the 
mould ;  or  by  using  a  thin  tube  instead  of  a  glass  rod,  and 
breaking  it  to  pieces  when  the  tube  is  finished,  if  it  should 
happen  to  adhere.  Great  care  is  necessary,  in  using  the 
flour,  that  none  get  to  the  surfaces  to  be  joined,  for  any 
kind  of  dirt  or  extraneous  substance  prevents  the  adhesion, 
and  the  tube  is  rendered  imperfect.  On  the  other  hand, 
when  the  tube  is  finished,  and  it  is  desirable  to  prevent  the 

*  Mr  Hancock  resides  in  Goswell  Mews,  Goswell-street  Road. 


CAOUTCHOUC  CONNECTERS.  219 

adhesion  from  pressure  of  the  sides  within,  then  a  little  flour, 
chalk,  or  other  dry  powder  is  very  useful. 

450.  If  Hancock's  sheet  caoutchouc  cannot  be  obtained, 
the  tube  may  be  made  of  thin  bottle  India-rubber.     For  this 
purpose,  the  smallest  and  thinnest  bottles  should  be  chosen, 
selecting  from  them,  when  cut  up,  only  the  most  straight 
and  uniform  pieces  that  can  be  obtained.     They  should 
first  be  softened  by  being  placed  in  a  warm  situation  for 
some  hours  and  rubbed  frequently,  or  by  being  boiled  for 
half  an  hour ;  then,  being  dried,  they  may  be  formed  into 
tubes.     The  caoutchouc  in  bottles  is  more  rigid  and  stiff, 
and  less  adhesive,  than  that  in  sheets,  and  for  this  reason, 
greater  pressure  and  more  care  are  generally  required  in 
making  the  joint  firm  and  tight ;  the  tubes  will  probably  re- 
quire warming  two  or  three  times  on  the  rod  during  the 
operation  of  pressing  the  edges  together,  and  perhaps,  also, 
compression  of  the  joint  by  a  pair  of  pincers. 

451.  Although  these  tubes  have  been  described  as  cylin- 
drical, yet  they  are  frequently  useful  of  a  conical  form  to 
connect  tubes  or  apertures  of  different  sizes  (844).     There 
is  no  ordinary  agent,  except  perhaps  chlorine  and  strong 
nitric  and  sulphuric  acids,  which  act  upon  them;  hence 
they  are  very  generally  applicable.     When  tubes  are  con- 
nected by  them,  as  in  the  present  case  of  sulphurous  acid, 
one  of  these  flexible  connecters  should  be  selected  of  a  size 
near  to  that  of  the  tube  to  which  it  is  to  be  adapted.     If 
small,  it  easily  admits  of  extension,  and  is  then  slipped  over 
the  ends  and  tied  with  two  or  three  turns  of  fine  twine  or 
thread,  which  should  not  be  drawn  tight,  or  it  will  cut  the 
caoutchouc;  indeed,  when  the  tube  has  required  a  little 
expansion  to  make  it  pass  over  the  glass,  it  contracts  with 
sufficient  force  to  form  a  joint  impervious  to  gas  at  ordinary 
pressure  ;  very  little  stress,  therefore,  upon  the  thread  is 
sufficient  to  secure  any  joint  in  a  perfect  manner.     If  the 
caoutchouc  tube  be  a  little  too  large,  so  contractile   and 
manageable  is  the  substance,  that  tying  is  quite  sufficient  to 
make  it  tight. 

452.  Where  the  object,  as  in  the  present  case,  is  merely 
to  connect  different  parts  of  an  apparatus,  the  ends  of  the 


220  DISTILLATION REFRIGERATION, 

glass  tubes  should  be  from  the  eighth  to  the  fourth  of  an 
inch  apart  within  the  caoutchouc  connecters.  This  is  quite 
sufficient,  in  ordinary  cases,  to  allow  of  that  flexibility  in 
complicated  glass  apparatus  which  is  so  valuable  as  permit- 
ting motion  and  the  minute  adjustments  of  one  part,  without 
endangering  another.* 

453.  The  apparatus  for  a  distillation  of  this  kind  at  low 
temperatures  being  thus  connected,  and  ready  for  an  opera- 
tion, the  next  step  is  to  apply  the  necessary  means  of  cool- 
ing the  parts  where  condensation  is  to  be  effected.     For 
this  purpose  some  ice  should  be  pulverized,  the  glass  a  half 
filled  with  it,  and  then  nearly  filled  up  with  water.     For  the 
glass  6,  where  the  actual  condensation  is  to  take  place,  a 
more  powerful  cooling  mixture  must  be  prepared ;  for  this 
purpose  ice  and  salt  should  be  used,  the  glass  being  filled 
with  the  mixture  to  within  half  an  inch  of  the  top. 

454.  In  making  this  mixture,  a  little  ice  should  first  be  put 
into  a  mortar,  and  having  been  broken  small,  during  which 
operation  the  mortar  will  have  cooled  considerably,  should 
have  about  a  fourth  of  its  bulk  of  salt  added  and  rubbed  with 

*      • 

*  When  sheet  caoutchouc  cannot  be  purchased,  it  may  be  made  by  soaking 
bags  of  that  substance  in  impure  or  common  ether  for  several  days,  and  then  in- 
flating them  by  means  of  the  breath  applied  through  a  tube  tied  to  the  mouths 
of  the  bags.  At  from  50°  to  70°  (Fahrenheit)  ether  of  about  the  specific  gravity 
of  764  will  be  sufficiently  strong,  provided  the  bags  are  suffered  to  lie  in  it  not 
less  than  three  or  four  days.  Between  740  and  750,  ether  is  the  best  adapted 
to  the  purpose,  and  will  soften,  without  injuring  the  texture,  of  the  gum  elas- 
tic.— When  very  thin  bags,  to  be  used  as  balloons,  are  to  be  made,  the  ether 
should  be  strong,  the  time  of  immersion  short,  and  the  inflation  immediate,  on 
the  removal  from  the  liquid. — But  when  gas-holders,  or  bags  for  making  sheet 
caoutchouc  are  desired,  the  ether  should  be  weak,  the  maceration  prolonged, 
and  the  attempt  at  inflation  should  not  be  commenced  until  the  surfaces  are 
dried,  and  the  interior  dusted  over  with  finely  powdered  starch. — If  the  bag  be 
of  unequal  thickness,  the  hands  should  be  so  applied  as  to  support  the  thinner 
parts,  and  thus  force  the  thicker  parts  to  expand  first.  The  operation  is  one  of 
easy  application  after  some  practice,  but  is  almost  sure  to  fail  in  the  hands  of 
a  careless  or  unpractised  manipulator.— If  done  in  a  cold  atmosphere,  or  if  the 
evaporation  produce  too  much  coldness,  the  bags  become  rigid  and  break  rather 
than  expand  ;  but  if  the  temperature  be  above  50°  F.,  and  if  the  bag  be  occa- 
sionally suffered  to  contract  when  it  makes  itself  too  cold,  the  process  will  usu- 
ally prove  successful.— The  starch  is  necessary  to  prevent  the  agglutination  of 
the  sides  of  the  bags  which  are  rendered  adhesive  by  the  ether. — The  formal 
preparation  of  caoutchouc  tubes  is  unnecessary  because  pieces  wrapped  round 
the  glass  tubes  to  be  united  serve  all  (he  purposes  required. — ED. 


DISTILLATION—REFRIGERATION.  221 

it :  fusion  of  much  of  the  ice  will  take  place,  and  a  cold  of  0° 
will  be  produced*.  After  a  few  minutes  this  portion  is  to 
be  thrown  away,  for,  being  fluid,  it  would  not  long  retain  its 
low  temperature  in  a  warm  atmosphere,  and  its  use  should 
therefore  be  confined  to  cooling  the  mortar  and  pestle.  The 
operator  should  now  proceed  to  pound  ice  and  salt  together 
for  a  mixture  to  be  used  in  the  distillation.  The  quantity  of 
salt  used  should  be  about  one-half  the  weight  of  the  ice,  or 
nearly  one-third  its  bulk  ;  this  is  far  more  than  the  water  from 
the  ice  can  dissolve,  but  the  excess  is  necessary  to  insure, 
with  facility,  the  cold  of  0°,  as  long  as  ice  continues  undis- 
solved.  The  pulverization  of  the  ice,  and  its  mixture  with 
salt,  should  not  be  discontinued  as  soon  as  the  temperature 
in  the  mortar  is  at  0°,  but  continued,  consistently  with  a  quick 
operation,  until  the  ice  is  as  small  as  possible  ;  otherwise, 
after  being  put  into  the  glass,  and  standing  for  a  time,  a 
quantity  of  liquid  will  form,  the  solid  salt  will  sink,  the  lumps 
of  ice  float,  and  it  will  be  found  difficult  by  stirring-  to  keep 
the  temperature  down  to  0°;  whereas,  if  the  ice  be  in  fine 
particles,  when,  from  the  production  of  brine,  a  partial  sepa- 
ration does  take  place,  very  little  stirring  will  be  sufficient 
to  keep  the  temperature  at  0°,  until  nearly  all  the  ice  be  dis- 
solved. The  state  of  the  mixture  in  the  mortar  is  most  ad- 
vantageous when,  with  a  due  proportion  of  salt,  it  contains 
most  solid  ice  in  a  small  state. 

455.  Neither  a  cold  mixture,  nor  ice  and  water,  should 
be  poured  suddenly  into  a  glass  at  common  temperatures  :  it 
is  safer  to  cool  the  glasses  previously  by  putting  a  few  pieces 
of  ice  into  them,  and  then,  upon  removing  the  ice,  to  intro- 
duce the  mixtures.     The  receivers,  which  are  to  be  placed 
in  the  cooling  mixture,  should  also  have  their  temperatures 
lowered  gradually  ;  this  is  easily  effected  by  allowing  them 
to  remain  for  a  few  moments  among  the  loose  ice. 

456.  It  may  be  observed  that  so  long  as  the  glass  a  con- 
tains ice  mixed  with  water,  the  water  will  beat  32°  or  nearly 

"'  The  reduction  of  ice  to  a  coarse  powder  is  not  easily  effected  in  the  usual 
way  in  a  mortar,  but  is  almost  instantly  accomplished  by  folding  it  in  a  coarse 
towel,  striking  it  so  as  to  form  fragments,  and  then  rolling  it  with  any  cylin- 
der.—ED. 


222  DISTILLATION — SULPHUROUS  ACID. 

so ;  and  in  the  glass  6,  if  stirred  now  and  then,  the  tempera- 
ture of  the  whole  will  remain  nearly  at  0°,  so  long  as  both 
ice  and  salt  in  any  quantity  remain  in  the  solid  state.  But 
if  the  operation  should  continue  until  nearly  the  whole  of  the 
ice  in  both  is  dissolved,  it  is  better  not  to  wait  till  all  has 
disappeared,  but,  whilst  a  fifth  or  a  sixth  part  remains,  to 
prepare  a  fresh  mixture  for  6,  and,  removing  part  of  the  wa- 
ter from  a,  to  replace  it  by  ice. 

457.  These  cooling  mixtures  receive  heat  so  rapidly  from 
the  atmosphere,  especially  in  summer,  as  often  to  have  their 
power  exhausted  in  one-half  or  one-third  the  time  during 
which  they  would  remain  effectual  if  such  influence  were 
prevented.     When  operations,  therefore,  of  any  kind  in  which 
refrigerating  mixtures  are  used,  are  continued  for  a  long 
time,  it  is  highly  advantageous  to  prevent  the  effect  as  much 
as  possible,  that  the  trouble,  expense,  and  loss  of  time  atten- 
dant upon  the  frequent  renewal,  may  be  avoided.     All  that 
is  necessary  is  to  hinder  the  access  of  air,  either  by  wrapping 
a  dry  flannel  or  cloth  round  the  sides  of  the  cooling  vessel, 
or  even  a  large  sheet  of  paper  three  or  four  times  loosely 
round  it,  so  as  to  form  a  cylinder,  which  is  to  be  tied  with 
pack-thread  (1343).     This  case  should  rest  upon  the  table 
beneath,  so  as  to  prevent  as  much  as  possible  the  passage  of 
air  at  the  bottom  :  not  that  small  apertures  need  be  attended 
to,  but  free  way  for  a  descending  current  should  not  be  per- 
mitted.    The  tops  of  the  vessels  may  be  covered  temporarily 
by  laying  on  them  loosely  a  card  or  a  couple  of  cards  with 
notches,  to  receive  the  tubes.     Small  portions  of  freezing 
mixtures  may  in  this  way  be  preserved  for  hours  together,  at 
0°,  in  the  middle  of  summer.     In  hot  weather,  merely  put- 
ting the  glass  containing  the  refrigerating  mixture  into  a 
glass  jar  is  very  useful,  for  the  latter  retains  a  bath  of  cold 
air  around  the  former  which  retards  the  alteration  of  temper 
rature  very  greatly.     The  jar  should  be  covered  with  a  card, 
or  paper,  to  keep  the  atmosphere  within  in  a  quiescent  state. 

458.  Having  made  the  proper  preparatory  arrangements, 
the  distillation  of  the  sulphurous  acid  may  be  commenced 
and  carried  on*.     The  gas,  being  liberated  from  any  of  the 
usual  materials  in  the  retort,  passes  first  through  the  bent 

*  See  p  217. 


DISTILLATION SMALL  RECEIVERS.  223 

tube  retained  at  a  temperature  of  32°  by  the  ice  and  water. 
Several  advantages  result  from  the  use  of  this  vessel.  In  the 
first  place,  water  brought  over  with  the  gas  is  in  part  con- 
densed and  retained  ;  in  the  second,  the  temperature  of  the 
gas  is  reduced  to  32°,  and  consequently  its  condensation 
more  easily  effected  in  the  receiver  at  b  ;  in  the  third,  being 
evolved  in  a  warm  state,  much  of  the  heat  which  must  ne- 
cessarily be  abstracted  from  it  before  it  will  assume  the  li- 
quid form  is  removed  here,  where  the  refrigerating  agent 
(ice  and  water)  is  easily  restored,  and  consequently  less  of 
the  cooling  power  of  the  mixture  in  b  is  required  for  its  ul- 
timate condensation,  and  the  latter  remains  effectual  for  a 
longer  time. 

459.  Leaving  the  part  of  the  apparatus  at  a,  the  sulphu- 
rous acid  travels  on   to  6,  and  there  enters  the  receiver. 
Being  heavy,  it  soon  displaces  the  air ;  and  then,  coming  in 
its  unmixed  state  against  the  sides  of  the  receiver  at  0°,  it  is 
condensed  and  assumes  the  liquid  form.    This  condensation, 
as  the  student  will  know  from  his  scientific  >sources  of  che- 
mical knowledge,  evolves  heat,  and  will  consequently  tend 
to  raise  the  temperature  of  the  mixture  around  the  receiver: 
in  this,  and  in  all  similar  operations,  a  thermometer  should 
therefore  be  immersed  in  the  mixture,  to  indicate  whether  its 
temperature  is  such  as  it  ought  to  be. 

460.  It  will  be  found  advisable,  in  all  cases  where  the 
substance  distilled  is  so  volatile  as  to  require  these  low  tem- 
peratures for  its  condensation,  to  collect  it  in  small  receiv- 
ers ;  not  only  that  it  may  soon  come  into  contact  with  their 
cold  sides  during  condensation,  but  also  that  it  may  be  in 
convenient  portions  for  operating  with  in  experimental  inves- 
tigations (924,  929).     The  vessel  in  which  the  body  is  con- 
densed should  generally  be  that  in  which  it  is  afterwards 
preserved  ;  and  as,  in  most  experiments,  the  quantity  in  one 
vessel  will  (unless  with  peculiar  management)  be  used  at 
once,  it  is  better  in  the  first  instance  to  receive  the  substance 
in  such  small  portions  as,  being  sufficient  for  each  time,  shall 
leave  no  overplus ;  so  that  waste  may  be  avoided.     Operat- 
ing m  this  way,  it  will  be  necessary  to  change  the  receivers 
frequently  :  this  is  easily  done  in  consequence  of  the  flexi- 


224  DISTILLATION — RETORT  NECK  ELONGATED. 

bility  of  the  arrangements.  Those  receivers,  which  are  to 
replace  in  succession  such  as  are  sufficiently  full,  should  be 
preserved  cool  by  a  mixture  in  a  separate  glass. 

461.  The  receivers  may  in  many  cases  be  small  flasks  or 
stoppered  bottles,  but  the  latter  are  generally  so  thick  at  the 
bottom  as  to  fly  to  pieces  when  one  of  them  containing  such 
a  volatile  body  as  sulphurous  acid  is  opened,  in  consequence 
of  the  sudden  cold  produced  by  its  evaporation.     Very  use- 
ful receivers  for  these  purposes  will  be  described  in  Sect. 
xvi. 

462.  The  various  circumstances  necessary  to  an  effectual 
arrangement  for  a  distillation  of  this  kind  have  now  been 

^described  minutely.  It  will  be  necessary  to  point  out  the 
applicability  of  parts  only  of  the  arrangements — their  uses  in 
the  present  instance  will  be  so  evident  as  to  indicate  their 
sufficiency  in  other  cases;  and  though  a  particular  form  of 
the  tubes  has  been  described,  yet  the  parts  may  easily  be 
altered  and  arranged  at  pleasure. 

463.  There|ip,  however,  one  point  with  respect  to  the  re- 
tort worth  suggesting,  as  it  will  often  be  found  useful.     It 
is  the  advantage  derived  from  an  elongation  of  the  neck  of 
the  retort  itself  at  the  table  blow-pipe  (1179,  1176),  by  sof- 
tening and  drawing  it  out  sometimes  almost  to  a  capillary 
tube ;  and  also  by  bending  it   in  different  directions  up- 
wards or  downwards.     Opportunities  are  thus  obtained  of 
delivering  the  products  of  the  distillation  through  minute 
apertures,  and  upon  particular  spots,  in  a  very  advantageous 
manner.     Similar  opportunities  of  course  exist  with  respect 
to  the  tube  which  terminates  the  distillatory  apparatus  (448). 

464.  In  the  apparatus  and  arrangements  hitherto  describ- 
ed, the  passage  is  free  from  the  retort  to  the  air,  and  in  the 
distillation  of  sulphurous  acid  it  will  generally  be  found  that 
much  of  the   substance   escapes  and    is    lost.     In    some 
operations   this   is  carefully   to   be   avoided:  thus   in  the 
distillation  of  wine  for  the  purpose  of  ascertaining  the  quan- 
tity of  ^alcohol  it  contains,  if  vapour  be  lost,  alcohol  is  lost, 
and  the  results  are  inaccurate.     In  other  cases,  as  in  the  pre- 
paration of  concentrated  hydro-cyanic  acid,  though  the  exact 
quantity  of  the  product  is  not  required,  yet  being  valuable 


DISTILLATION CLOSE  APPARATUS. 


225 


and  also  deleterious  to  the  lungs,  it  is  desirable  to  prevent 
Joss  as  much  as  possible.  Some  arrangements  will,  there- 
fore, now  be  described  tending  to  secure  all  the  results,  and 
allowing  at  the  same  time  of  the  introduction  and  illustration 
of  other  contrivances. 

465.  Let  us  suppose  the  object  were  to  distil  some  wine 
for  the  purpose,  as  already  intimated,  of  separating  the  alco- 
hol it  contains  from  the  other  principles,  that  its  quantity 
may  be  accurately  estimated  ;  and  let  us  consider  it  as  hav- 
ing been  introduced  into  a  tubulated  retort  with  the  precau- 
tions already  described  to  prevent  soiling  the  neck  (437), 
and  with  the  introduction  also  of  some  clipped  platinum  foil 
and  two  or  three  pieces  of  cork  which  may  have  little  pieces 

of  platinum  foil  stuck  into 
them  (441).  The  wood-cut 
represents  this  retort  con- 
nected witfi  a  quilled  recei- 
ver which  is  to  assist  in  the 
condensation,  and  of  which 
the  quill  descends  into  a 
flask  which  is  to  receive  the 
distilled  spirit.  The  retort 
should  have  a  neck  of 
comparatively  considerable 
length  ;  for,  by  a  contrivance  to  be  described,  a  large  por- 
tion of  it  is  to  serve  as  a  refrigerator.  If  from  14  to  18 
inches  long  it  will  answer  the  purpose. 

466.  The  retort  and  receiver  are  connected  by  a  cork,  and 
it  is  better  that  the  neck  of  the  retortand  the  opening  of  the 
receiver  should  be  of  very  different  dimensions,  than  that 
they  should  nearly  fit.     If  the  aperture  of  the  receiver  be« 
about  two  inches  in  diameter,  it  will  be  large  enough  to  ad- 
mit the  necks  of  most  retorts.     A  bung  of  good  cork  (1331), 
chosen  of  such  size  that  it  will  fit  tightly  into  the  aperture 
of  the  receiver,  should  be  pierced  as  before  described  (67), 
the  hole  being  of  such  dimensions,  that,  when  the  neck  of  the 
retort  is  thrust  tightly  into  it  and  then  connected  with  the 
receiver,  the  beak  may  pass  in  about  as  far  as  is  represented 

2  D 


226  RETORT  AND  RECEIVER  CONJOINED. 

in  the  woodcut.  If  the  cork  be  good,  well  cut,  and  the  hole 
neatly  made,  this  junction  will  be  air-tight,  or  nearly  so,  and 
may  be  made  quite  secure  by  drawing  a  slip  of  moist  bladder 
tightly  round  it  several  times,  and  tying  it  on  by  a  few  turns 
of  twine. 

467.  The  flask  should  be  of  such  a  size  as  to  permit  the 
quill  of  the  receiver  to  approach  close  to,  or  to  touch  the 
bottom.     It  should  be  immersed  in  a  jar  of  water,  and  a  few 
pieces  of  ice  should  be  put  into  the  jar  and  allowed  to  float 
on  the  surface,  for  the  purpose  of  keeping  the  tempera- 
ture at  or  below  40°.     The  flask,  whilst  empty,  will  be  so 
much  buoyed  up  by  the  water,  as  to  press  against  the  end  of 
the  quill  if  its  aperture  be  large  enough  to  admit  the  latter 
so  far  through  it ;  but  this  sould  be  prevented,  as  it  endan- 
gers the  bottom  of  the  flask.     A  little  slip  or  wedge  of  wood 
introduced  between  the  quill  and  the  flask  at  the  neck,  will 
retain  the  latter,  so  that  the  end  of  the  quill  may  be  about  a 
quarter  of  an  inch  from  the  bottom.     So  much  pure  water 
should  be  put  into  the  flask  as  to  rise  just  high  enough  to 
close  the  aperture  of  the  quill. 

468.  Both  receiver  and  flask  are  in  this  way  adapted  for 
refrigeration ;  but  the  intention  is  not  to  effect  the  principal 
condensation  there,  but  to  insure  the  retention  of  all  the  spirit 
by  liquefying  such  portions  as  may  pass  the  neck,  where  the 
condensation  is  principally  to  be  effected  in  the  manner  now 
to  be  described.     A  little  loose  tow  should  be  drawn  out 
into  a  sliver,  wetted,  and  wrapped  twice  round  the  neck  of 
the  retort,  the  ends  being  so  long  that  they  may  be  twisted 
together  beneath,  with  a  few  threads  of  the  tow  pulled  out 
from  the  part  that  has  already  passed  round,  and  hang  down 
for  about  four  or  five  inches  in  length.     The  ring  of  tow 
which  thus  surrounds  the  neck  should  be  placed  about  half 
an  inch  or  an  inch  above  the  junction  before  mentioned,  as 
at  a  (465) ;  it  should  be  moderately  tight  around  the  glass, 
and  should  be  carefully  separated  from  the  bladder  or  cork 
beyond,  so  as  to  have  no  part  in  contact  with  it,  touching 
indeed  nothing  but  the  neck.     A  single  piece  of  filtering 
paper  should  then  be  selected,  long  enough  to  reach  from 
about  half  an  inch  above  the  tow  to  the  part  where  the  neck 


REFRIGERATION  ON  RETORT  NECK.  227 

begins  to  turn  and  blend  with  the  body  of  the  retort,  and 
wide  enough  to  go  two-thirds  of  nearly  the  whole  way  round 
the  neck  :  it  should  not  pass  quite  round,  as  it  then  does  not 
apply  itself  so  readily  in  the  wet  and  dry  state  to  the  glass. 

Being  laid  on  the  neck  of  the  re- 
tort and  moistened,  it  will  adapt 
itself  to  the  glass,  adhere  closely 
to  it,  and  will  serve  the  office  of 
conveying  water  to  every  part  to 
which  it  is  applied ;  and  it  should  be  observed  that  all  parts 
of  this  surface  is  of  such  inclination,  that  the  fluid  condensed 
within  will  run  into  the  receiver,  and  not  return  again  to  the 
body  of  the  retort. 

469.  The  water  is  to  be  supplied  to  this  paper  from  a  fil- 
ter in  a  funnel  placed  above  (534,  &c.),  in  such  a  position 
that  the  drops  shall  have  to  fall  about  half  an  inch  or  an 
inch,  which  assists  in  spreading  the  water  over  the  paper, 
and  also  shall  descend  upon  the  paper  a  little  way  from  its 
upper  extremity.     If  they  fall  on  to  its  edge,  or  on  to  the 
glass,  a  few  particles  may  splash  upon  the  hotter  parts  of 
the  retort,  or  portions  may  run  down  its  outside.     Water 
should  be  put  into  the  filter  in  such  quantity,  that  it  may 
descend  sometimes  in   a  small  stream,  and  sometimes  in 
rapid  drops  :  it  will  wet  the  paper  and  the  glass  under  it, 
and  running  down  to  the  tow,  will  there  descend  and  be 
caught  in  a  basin  placed  beneath,  not  a  particle  passing  be- 
yond the  tow  to  endanger  the  introduction  of  any  portion 
into  the  flask,  either  by  soaking  through  the  bladder,  or  by 
running  down  the  outside  of  the  receiver  and  the  quill. 

470.  Still,  however,  the  water,  in  its  tendency  to  descend, 
will  not  wet  all  parts  of  the  paper  full>and  equally  if  it  be 

of  much  extent;  and  the  upper  surface  of  the  lower 
end  incurs  the  risk  of  being  sometimes  dry.  This 
is  avoided,  and  the  paper  freely  wetted  in  all  parts 
by  the  use  of  another  piece  of  filtering  paper  folded  as  here 
drawn.  Being  placed  with  its  two  lower  edges  upon  a  moist 
surface,  it  will  absorb  water,  the  two  sides  or  flaps  will  bend 
down,  and,  accommodating  themselves  to  the  wet  surface 
beneath,  will  adhere  to  it,  and  the  central  part  will  stand  up 


228  DISTILLATION  PERFORMED. 

in  a  ridge,  leaving  an  acute  angled  space  between  it  and 
the  moistened  surface.  Being,  therefore,  applied  to  the 
neck  of  the  retort,  it  adheres,  is  stationed  there  like  a  saddle, 
and  answers  the  purpose  of  a  channel  for  the  water.  Its 
proportions  and  position  may  be  gathered  from  the  former 
wood-cuts.  The  water  which  drops  upon  the  neck,  just 
above  its  upper  opening,  partly  enters  into  the  channel 
there  formed  ;  and  whilst  about  a  third  of  it  is  carried 
through,  and  delivered  at  the  lower  end  of  the  channel  over 
the  upper  surface  of  the  neck,  the  rest  flows  out  along  the 
sides  of  the  saddle,  and  being  distributed  all  over  the  paper 
adhering  to  the  glass,  keeps  it  thoroughly  wet  and  even  flow- 
ing with  moisture. 

471.  All  is  now  prepared  for  distillation:  heat  is  to  be 
applied  to  the  retort,  and  when  the  upper  part  becomes 
warm,  the  filter  must  be  supplied  with  water,  so  that  the  con- 
densing arrangement  on   the  neck  may   be  constantly  and 
fully  moistened.     Upon  commencing  ebullition,  the  tempe- 
rature of  the  neck  will  rise,  water  will  rapidly  evaporate 
from  the  moist  paper,  and  care  must  be  taken  that  the  supply 
be  sufficient,  not  merely  to  keep  the  paper  fully  wet,  not- 
withstanding the  evaporation,  but  to  have  a  surplus  running 
off  in  a  small  stream  from  the  tow.     The  distillation  should 
not  be  hurried,  and  the  quilled  receiver  should  never  be 
more  than  warm  about  the  part  where  the  retort  is  inserted. 
If  it  become  hot,  or  if  vapour  enters  it  visibly  from  the  re- 
tort, rising  and  causing  rapid  condensation  over  the  whole 
of  the  upper  surface  and  elevating  its  temperature,  then  either 
more  water  must  be  suffered  to  fall  upon  the  neck,  or  if  that 
be  fully  moistened,  and  still  does  not  effect  a  sufficient  con- 
densation, the  heat  must  be  diminished. 

472.  The  tightness  of  the  junction  between  the  retort 
and  receiver  will  be  rendered  evident  upon  the  application 
of  heat,  by  the  expansion  of  the  air  within,  and  its  passage 
from  the  bottom  of  the  beak  in  bubbles  through  the  water. 
This  will  continue  until  much  of  the  air  is  expelled,  and  the 
retort  and  part  of  the  neck  is  filled  with  vapour.     As  the 
distillation  proceeds,  the  condensed  liquid  will  flow  down 
to  the  water  in  the  flask  and  mix  with  it.     The  first  portion 


"DISTILLATION  CONCLUDED.  229 

which  rises  is  the  most  volatile ;  but,  combining  with  the 
water,  and  being  diluted  by  it,  and  its  temperature  being 
reduced  at  the  same  time  to  about  40°,  no  appreciable  por- 
tion will  escape.  As  the  quantity  of  fluid  increases,  the 
quill  will  be  more  deeply  immersed,  but  this  is  of  no  con- 
sequence :  the  fluid  will  rise  and  fall  in  it,  and  occasionally 
when  the  heat  slackens,  or  when  fresh  water  has  been  put 
into  the  filter,  the  condensation  within  may  be  such  that 
nearly  all  the  contents  in  the  flask  may  pass  up  into  the 
globe,  and  even  air  enter  it.  This  is  of  no  importance; 
there  is  abundant  space  in  the  globe  for  the  liquid,  so  that 
it  cannot  be  drawn  back  into  the  retort,  and  it  even  has  the 
advantage  of  cooling  that  vessel ;  in  a  few  minutes  the  ex- 
pansion within  will  cause  it  again  to  return  into  the  flask, 
and  probably  a  portion  of  the  air  previously  absorbed  may 
now  be  expelled.  When  about  five-sixths  of  the  contents 
of  the  retort  have  passed  over,  all  the  alcohol  will  have  been 
separated,  and  the  operation  may  be  concluded  :  the  diluted 
spirit  in  the  flask  or  flasks,  if  a  second  has  been  required, 
being  reserved  for  the  prosecution  of  the  intended  experi- 
ments. 

473.  It  is  sometimes  necessary  in  distillatory  processes  to 
keep  a  part  of  the  neck  hot,  for  the  purpose  of  preventing 
the  condensation  of  the  vapours  there.     This  is  readily  ef- 
fected by  wrapping  it  in  two  or  three  folds  of  dry  flannel 
or  cloth,  or  even  paper,  the  envelope  being  loose  and  tied 
with  twine. 

474.  The  refrigerating  arrangement  (468),  although  de- 
scribed of  such  a  size  as  to  occupy  nearly  the  whole  of  the 
neck,  may  vary  in  extent  and  form,  and  be  applied  to  other 
apparatus,  as  well  as  the  neck  of  a  glass  retort. 

475.  In  other  cases  of  distillation,  it  may  be  required  to 
condense  the  liquid  products  out  of  contact  with  other  sub- 
stances, and  yet  to  retain  the  uncondensed  portions,  so  as  to 
pass  them  through  water,  or,  if  gaseous,  to  conduct  them  to 
their  proper  receptacles.     The  accompanying  figure  will  il- 
lustrate a  case  of  this  kind,  which  may  be  supposed  to  be 
a  distillation  of  nitric  acid  from  nitre  and  sulphuric  acid. 
The  retort  containing  the  charge  is  connected  with  a  globu- 
lar receiver  of  the  form  a,  from  which  a  bent  tube  proceeds, 


CONDENSATION  OF  PRODUCTS. 

and   passes   into   the   Woulfe's 
bottle  b  (844).     The  junctions 
between  the  receiver   and   the 
retort  and  tube  are  best  made 
by  ground  glass  joints  ;  but  if 
that  plan  cannot  be  adopted,  other  means  must  be  resorted 
to.     Good  pierced  corks  will  answer  the  purpose,  the  junc- 
tion being  made  vapour-tight,  either  by  some  glazier's  put- 
ty put  over  it,  or  a  paste  of  linseed  meal  (1031),  or  a  little 
plaster  of  Paris  ;  and  where  the  neck  or  tube  nearly  fits  the 
aperture,  it  may  be  made  tight  without  a  cork  by  plaster  of 
Paris  alone ;  the  open  space  being  first  closed  by  rather  a 
thick  paste  of  it,  and  the  joint  made  smooth  and  tight  out- 
side by  a  thinner  portion  (1108).     The  plaster  will  resist 
the  action  of  the  acid  vapours  ;  cork  and  other  substances 
will  be  somewhat  acted  upon,  but  with  care  will  cause  no 
injury  to  the  results.     If  bodies,  not  corrosive,  are  distilled 
in  this  way,  these  precautions,  as  to  the  nature  of  the  clos- 
ing substances,  are  not  necessary  (Sect,  xviii).^ 

476.  The  receiver  a,  and  the  bottle  6  may,  one  or  both, 
be  cooled,  according  to  the  temperature  produced  by  the 
vapour,  being  for  that  purpose  immersed  in  jars  or  pans  of 
water ;  the  neck  of  the  retort  may,  occasionally,  be  cooled 
as  before  by  paper  and  the  filter  (468).  Caution  must  be 
used  in  applying  that  method  however  to  such  substances, 
as,  from  the  high  temperature  at  which  they  boil,  produce 
very  hot  vapours,  lest  the  differences  of  temperature  be  so 
great  as  to  break  the  glass.  Bodies,  not  more  fixed  than 
water,  may,  when  distilled  in  glass  retorts,  have  that  process 
applied ;  but,  when  substances  requiring  higher  tempera- 
tures, for  example,  nitric  acid  or  oil  of  turpentine,  are  dis- 
tilled, then  hot  water  should  be  put  into  the  filter  instead  of 
cold,  or  the  refrigeration  should  be  carried  on  further  down 
the  neck,  where  the  contents  are  of  a  lower  temperature. 

477.  At  the  commencement  of  the  operation,  it  is  sup- 
posed that  the  receiver  a  is  clean  and  dry,  and  that  the  bot- 
tle b  contains  water  enough  to  cover  the  end  of  the  tube. 

*  By  bending  the  neck  of  the  retort  so  that  a  portion  of  it  may  enter  vertically 
the  mouth  of  a  bottle,  surrounded  by  a  cooling  apparatus,  the  nitric  acid  may 
be  made  without  the  trouble  of  forming  more  than  one  junction. — ED. 


231 

In  the  distillation,  therefore,  any  product  condensed  in  the 
neck  of  the  retort,  or  in  the  receiver,  will  be  retained  in  an 
undiluted  and  unmixed  state ;  but  the  portions,  which,  from 
their  particular  nature,  or  the  comparatively  high  tempera- 
ture of  those  parts,  remain  uncondensed,  will  be  conducted 
into  the  bottle,  and  their  condensation  facilitated  by  the 
solvent  powers  of  the  water,  or  the  still  lower  temperature 
which  may  there  be  applied.  If  any  gaseous  matters  are 
evolved,  they  may  be  conducted  away  by  a  second  tube, 
and  treated  as  hereafter  to  be  described  (748). 

478.  There  are  one  or  two  additions  now  and  then  re- 
quired to  this  and  other  arrangements,  in  consequence  of 
occasional  peculiar  circumstances  to  which  they  are  subject. 
It  may  be  observed,  that  if  partial  condensation  of  the  va- 
porous atmosphere  in  the  retort  and  receiver  takes  place, 
the  solution  in  the  bottle  b  will  be  forced  back  into  the  re- 
ceiver a,  and  mix  with  its  contents  (475).     One  method  of 
avoiding  such  an  effect  is  by  the  use  of  Welter's  safety 

tube.  This  instrument  is  figured  in  the 
wood-cut,  and  may  be  fixed  into  the  tubu- 
lature  of  the  retort^  Mercury  is  to  be  in- 
troduced until  it  fills  about  one-fourth  of  the 
little  bulb,  and  the  tube  by  its  side,  to  the 
same  height ;  this  closes  the  passage,  but 
admits  of  a  variable  column  of  metal,  accor- 
ding to  the  pressure  within  the  retort  and 
receiver.  Whenever  there  is  condensation 
I  within,  the  external  air  has  a  tendency  to 

enter  by  forcing  the  water  up  the  tube  c  (in  the  former 
wood-cut),  and  the  mercury  into  the  ball  d  (of  the  present), 
and  will  gain  entrance  where  the  fluids  exert  the  least  pres- 
sure. Hence  it  is  necessary  to  have  the  height  of  the  tube 
c  above  the  water  in  the  bottle  &,  more  than  fifteen  times 
that,  from  the  bend  of  the  safety  tube  at  e,  to  the  level  of 
the  mercury,  when  nearly  the  whole  of  it  is  in  the  bulb  ;  for 
in  that  case,  the  air  will  enter  by  passing  through  the  mer- 
cury in  the  bulb,  and  not  by  forcing  the  water  into  the  re- 
ceiver at  a. 

479.  Should  it  be  impossible,  from  some  limiting  circum- 
stance, to  establish  this  proportion  of  1  to  15  or  more  in  the 


232  DISTILLATION — SAFETY-TUBE. 

height  of  the  column  of  mercury  and  fluid,  then,  in  place  of 
mercury,  water  may  be  used  in  the  safety  tube,  provided 
that  if  a  little  were  to  enter  the  retort  it  would  occasion  no 
injury,  but  then  the  height  from  e  to  the  top  of  the  safety  tube, 
should  be  two  or  three  times  the  quantity  by  which  the  tube 
c  (475)  dips  into  the  fluid  in  the  bottle,  otherwise  the  pres- 
sure of  the  gaseous  contents  may,  on  some  occasions,  force 
a  passage  out  through  the  safety  tube,  and  derange  the 
regularity  of  the  experiment. 

480.  It  is  to  be  observed,  that  a  few  bubbles  of  air  enter- 
ing by  the  safety  tube,  are  more  effectual  in  preventing 
further  contraction  of  the  vapours  within  the  retort,  than 
the  entrance  of  the  whole  of  the  water  by  the  tube  c  would 
be.     These  bubbles  come  at  once  into  the  hottest  part  of 
the  vessel,  are  there  much  expanded,  and  at  the  same  time 
actually  lessen  that  tendency  of  the  vapour  to  condense, 
which  is  at  the  moment  threatening  the  mischief;  whilst,  on 
the  contrary,  the  water  on  entering  would  rapidly  increase 
the  tendency  to  condensation,  both  by  cooling  the  receivers 
and  by  its  absorbent  power  over  the  vapours,  with  which  it 
would  be  brought  in  contact.     It  will  generally  be  found  in 
such  cases,  that  when  one  drop  of  water  has  entered,  the 
rest  will  rush  violently  after  it. 

481.  Another  arrangement  of  a  safety  tube  may  now  and 
then  be  adopted,  but  being   more  applicable  to   gaseous 
manipulations  will  hereafter  be  described  (847). 

482  A  contrivance  something  resembling  the  safety  tube 
just  described,  is  often  useful  in  feeding  a  retort  with  fluid 
during  the  progress  of  distillation.  For  this  purpose  a  piece 
of  tube  may  be  bent  into  the  form  of  a  double  syphon,  as  in 
the  figure,  and  fixed  into  the  tubulature  of  the  retort.  Acid 
poured  into  it  will  rise  in  the  first  two  por- 
tions to  the  height  of  the  second  bend,  and 
then  further  additions  will  flow  into  the 
vessel.  The  part  a  should  be  of  sufficient 
length  to  contain  a  column  of  fluid,  heavy 
enough  to  counteract  any  pressure  outwards 
that  may  occur  within :  its  length  should  be 
at  least  twice  that  of  the  middle  portion. 
Its  upper  extremity  should  be  opened  out 


DISTILLATION TEMPORARY  APPARATUS.  233 

at  the  blow-pipe  table  into  a  funnel  form,  and  the  tube  should 
be  so  large,  that  the  fluid  may  be  poured  down  without  car- 
rying air-bubbles  with  it.  If  it  be  so  small  that  air  mixes 
with  the  passing  fluid,  the  relative  weights  of  the  columns 
are  deranged,  and  sometimes  the  acid  thrown  back  and  even 
out  of  the  apparatus. 

483.  A  sufficient  number  of  instances  have  now  been  ad- 
duced; to  illustrate  the  different  arrangements  that  are  use- 
ful in  distillations  performed  with  glass  retorts.     But  little 
has  been  said  relative  to  the  methods  of  supporting  the  dif- 
ferent parts  in  their  respective  positions.     The 
delineations,   and   the    descriptions   relating    to 
flasks  (386),   retort  stands    (386),   bricks   (24), 
rings  (68),  wooden  blocks  (20),  &c.  being  suffi- 
cient for  the  purpose.     When  these  conveniences 
are  wanting,  very  useful  tripods  may  be  made,  by 
tying  three  sticks  together  at  the  middle,  and  con- 
fining them  beneath  by  string,  to  prevent  them  from  slip- 
ping down. 

484.  In  cases  of  necessity,  Florence  flasks  may  often  be 
substituted  for  retorts  in  distillation  ;  a  neck  being  formed 

of  a  piece  of  bent  tube,  and  attach 
ed  to  the  flask  by  a  good  sound 
cork,  made  tight  by  accurate  fitting 
without  bladder  or  lute.  Corks  thus 
circumstanced  sometimes  swell  by  the  heat  and  moisture 
so  much  as  to  endanger  the  neck  of  the  flask,  and  if  it  be 
discovered,  by  the  expansion  of  the  part  outside,  that  such 
danger  is  to  be  apprehended,  the  cork  should  be  partly 
withdrawn  and  in  that  way  relieved.  (373  Ed.) 

485.  Before  leaving   the   consideration   of   distillations, 
which  may  be  performed  at  temperatures  easily  borne  by 
glass,  there  are  one  or  two  remarks  to  be  made  in  addition 
to  those  already  given.     There  are  some  cases  in  which, 
although  the  heat  necessary  for  the  operation  may  be  easily 
sustained  by  glass  retorts,  circumstances  will  make  it  advisa- 
ble to  prefer  retorts  of  other  substances.     In  the  preparation 
of  fluoric  acid,  a  vessel  of  lead  will  be  superior :  glass 

2E 


234   RETORTS  NOT  OF  GLASS — VARIOUS  REFRIGERANTS. 

would  then  be  easily  acted  upon,  and  at  the  same  time  that 
the  retort  would  be  destroyed,  the  product  obtained  would 
not  be  pure,  but  a  combination,  with  a  part  of  the  vitreous 
matter.  There  are  some  substances  which,  though  suffi- 
ciently volatile,  are  very  difficult  of  distillation  in  glass  ves- 
sels. Of  such  kind  are  bone  oil,  Dipple's  animal  oil,  some- 
times naphtha,  and  some  of  the  common  essential  oils,  when 
free  from  water.  These  are  distilled  with  great  facility  in  a 
tin  plate  or  copper  retort,  but  as  they  frequently  require  a 
high  temperature,  the  vessels  should  not  be  soldered,  but 
be  either  brazed,  or  the  joints  lapped  over  and  then  made 
tight  by  a  small  quantity  of  solder. 

.486.  The  essential  oils  are  generally  distilled  with  water: 
they  rise  in  conjunction  with  its  vapour,  at  a  temperature  far 
below  that  at  which  they  would  distil  alone.  Advantage 
may  be  taken  of  this  circumstance  in  many  cases  where  the 
contact  of  water  is  of  no  consequence ;  and  bone  oil,  naph- 
tha, and  other  substances  of  that  kind,  may  be  distilled  in  a 
similar  manner.  It  is  to  be  remembered,  however,  on  future 
occasions,  that  the  substances  generally  retain  a  small  por- 
tion of  water,  which,  unless  removed,  may  be  injurious  in 
particular  experiments. 

487.  In  small  distillations,  other  cooling  agencies,  be- 
sides those  mentioned  (447,  448,  465),  are  useful.     With 
this  view,  alcohol,  ether,  carburet  of  sulphur,  and  even  sul- 
phurous acid,  are  employed  :  being  dropped  upon  the  con- 
densing vessel,  they  effect  their  object  by  rapid  evaporation. 
These  are  more  particularly  serviceable  in  small  operations, 
where  the  substances  are  distilled  by  cooling  the  receiver, 
instead  of  heating  the  retort.     Processes  of  this  kind  will 
be  described  and  illustrated  in  Section  xvi.  on  Tube  Chem- 
istry. 

488.  As  a  heated  tubulated  retort  cools,  it  is  advisable 
to  loosen  the  stopper  from  time  to  time,  lest  the  differences 
of  contraction,  from   previous   difference   of  temperature, 
should  cause  it  to  become  fixed  so  tightly  that  it  cannot  be 
removed  without  risk  of  breaking  the  vessel. 

489.  In  operations  of  distillation  requiring  temperatures 
so  high  that  glass  would  melt,  either  earthenware  or  iron 


RETORTS  COATED SUPPORTED   IN  THE  FURNACE.         235 

retorts  must  be  used,  or  the  glass  must  be  protected  and 
strengthened  by  an  exterior  coating  of  lute  (1084,  1093). 
Notwithstanding  the  fusibility  of  glass,  and  its  liability  to 
chemical  action  at  high  temperatures,  and  in  a  softened 
state,  it  is  still,  when  coated,  often  superior  to  earthenware, 
because  of  the  permeability  by  air  of  the  latter  substance 
when  hot,  and  its  great  risk  of  fracture  at  high  temperatures, 
either  during  the  heating  or  cooling;  and  it  is  often  pre- 
ferable to  iron,  because,  though  liable  to  chemical  action, 
it  is  generally  less  so  than  that  metal.  For  the  choice  of 
the  lute,  and  the  method  of  applying  it,  see  Section  xviii. 
Lutes,  Cements,  fyc. 

Glass  retorts  should  be  coated  at  a  leisure  time,  and  seve- 
ral of  them  kept  ready  for  use  in  a  warm  place  (16). 
Their  perfect  dryness  is  then  secured,  and  time  is  allowed 
for -the  stopping  of  any  cracks  that  may  have  been  formed. 

490.  When  perfectly  dry,  and  prepared  for  the  fire,  and 
charged  with  the  materials  to  be  distilled,  they  then  require 
to  be  adjusted  and  supported  in  a  furnace  that  they  may  be 
heated.  They  should  not  be  allowed  to  hang  from  the 
neck  as  is  frequently  permitted  in  ordinary  distillations, 
but  must  be  sustained  from  beneath,  that  when  the  glass  is 
red-hot  and  soft,  there  may  be  as  little  stress  or  weight  to 
disturb  its  form  as  possible  :  for  the  lute 
is  generally  so  much  cracked  by  the  heat, 
that  though  it  will  adhere  to  the  glass 
and  hang  together,  it  gives  on  the  whole 
very  little  strength  unless  supported  be- 
low ;  it  even,  by  its  weight,  sometimes  does  more  harm  than 
good.  A  very  excellent  support,  on  many  occasions,  is  a 
small  round  crucible  filled  with  sand,  and  placed  on  the 
bars  of  the  furnace,  the  bottom  of  the  retort  being  allowed 

Sto  rest  upon  it.     At  other  times,  a  couple  of  bars  of 
iron,  crossing  the  furnace,  are  used,  and  now  and  then 
stands,  either  of  wrought  or  cast-iron,  of  the  form 
figured,  and  of  different  sizes.    The  upper  wood-cut  repre- 
sents the  section  of  a  coated  glass  retort,  placed  within  a 
crucible  furnace  (158),  and  supported  on  a  crucible.    The 


236  RETORTS EARTHEN— IRON. 

furnace  is  notched  at  the  side  to  admit  of  the  passage  of  the 
retort  neck.* 

491.  Earthenware  retorts  are  made  of  very  different  ma- 
terials.    The  ware  is  sometimes  close  and  compact,  like 
that  of  Wedgwood,  that  the  vessels  may  be  but  little  per- 
meable to  air,  and  sometimes  more  open  and  coarse,  like 
the  red  or  brown  ware,  being  then  less  liable  to  crack  in 
the  fire.     They  should  be  heated  very  gradually,  and  also 
cooled  with  the  same  precautions,  if  it  be  desired  to  save 
them  from  fracture ;  but  it  is  Scarcely  worth  the  attempt  to 
use  an  earthenware  retort  a  second  time,  because  of  the 
difficulty  of  ascertaining  the  clean  state  of  the  inside,  and 
from  the  almost  inevitable  existence  of  fissures.     In  some 
cases  earthenware  retorts  may  be  rendered  tight,  i.  e.,  im- 
permeable to  air,  by  washing  their  surfaces  with  a  solution 
of  borax,  or  rather  with  a  cream  of  1  part  powdered  borax, 
2  of  finely-pulverized  glass,  and  water.     These  materials 
fuse  and  cover  the  surface  with  a  glaze,  which  effectually 
prevents  the  passage  of  air. 

492.  Earthenware  retorts  should  rarely  be  put  naked  into 
the  fire;  when  luted,  as  has  been  directed  with  regard  to 
glass  retorts  (489,  1084),  a  great  degree  of  security  beyond 
what  they  possess  when  naked,  is  afforded.     They  should 
be  carefully  dried  before  being  heated,  and  if  washed  with 
the  mixture  of  powdered  borax,  glass,  and  water,  previous 
to  the  application  of  the  lute,  are  rendered  impermeable  to 
air  or  vapour. 

493.  Small  iron  retorts  are  more  frequently  used  for  the 
distillation  of  oxygen  and  carbonic  oxide  gases,  than  for 
any  other  purpose.     They  are  usually  in  the  form  of  bottles 
having  an  iron  tube  fitted  to  them  by  a  ground  joint,  which 
answers  the  purpose  of  a  neck.     By  frequent  use,  this  joint 
oxidizes,  scales,  and  is  no  longer  quite  tight;  it  may  then 
be  rendered  so  by  mixing  up  a  little  fine  lute,  as  Cornish 
clay,  into  a  thin  paste,  with  either  water  or  oil,  and  putting 
it  round  the  tube  before  it  is  thrust  into  its  place  :  in  these 
cases  the  retort  should  be  introduced  very  steadily  and 

*  The  coarser  iron- wire-gauze,  as  suggested  by  Dr  Hare,  while  it  supports  well 
the  retort,  gives  passage  to  the  heat. — ED. 


SUBLIMATION — ALEMBICS FLASKS.  237 

carefully  into  the  fire,  lest  by 'shaking,  the  joint  should  be 
loosened.  As  little  of  the  oiled  substance  should  be  allow- 
ed to  pass  within  the  retort  as  possible.* 

494.  Distillations  with  the  iron  retort  are  best  effected  by 
a  coal  or  coke  fire.    The  table-furnace  fire  (169)  answers 
perfectly  well,  the  tube  of  the  retort  being  brought  out  eith- 
er at  the  door,  or  through  the  rings  put  on  above,  in  place 
of  the  sand-bath  (176).  * 

Sublimation. 

495.  The   apparatus    for  sublimation   in  the  laboratory 
consists  generally  of  tubes,  flasks,  retorts,  capsules,  and  cru- 
cibles.    Those  which  are  adopted  in  manufactories  being 
confined  to  particular  operations,  are  therefore  constructed 
of  such  materials  and  form,  as  fit  them  for  their  exclusive 
purposes.     The  use  of  tubes  in  the  sublimation  of  small 
quantities,  will  be  considered  hereafter  (935,  &c.).     Such 
substances  as  are  of  moderate  volatility,  like  naphthaline, 
iodine,  camphor,  chloride  of  carbon,  gallic  acid,  &c.,  rtiay 
be  sublimed  in  glass  retorts ;  the  vessel  being  heated  by  a 
lamp  or  sand-bath,  or  small  furnace,  and  the  neck  introduced 
into  a  large  globe  or  flask,  for  the  condensation  of  the  va- 
pours.    The  flask  may  either  be  cooled  or  not,  according 
to  the  circumstances  of  the  case,  the  means  being  those  be- 
fore described  (447,  &c.).     Florence  flasks  are  frequently 
superior  to  retorts  for  these  purposes,  and  being  placed  in 
an  inclined  position,  their  necks  may  be  introduced  into  re- 
ceivers, as  has  been  directed  with  respect  to  the  beak  of  the 
retort  (447.) 

496.  The  alembic  is  frequently  used  with  advantage  in 
the  sublimation  of  substances  of  moderate  volatility.     Its 
convenience  consists  in  the  facility  with  which  the  products 
and  residue  of  the  sublimation  may  be  removed.     There  is 
nothing  peculiar  in  its  use  requiring  notice. 

497.  Florence  flasks  are  useful  in  sublimations,  which  re- 
quire a  higher  temperature  than  the  substances  just  referred 

"The  cheapest  and  most  convenient  iron  retort  on  a  large  scale  is  a  quick- 
silver bottle,  to  the  female  screw  of  which  may  be  adjusted  a  male  screw  turned 
on  the  end  of  a  bent  gun  barrel.  Such  retorts  are  much  used  by  American 
chemists. — ED. 


238         SUBLIMATION APPARATUS PROCESS, 

to,  such,  for  instance,  as  calomel,  cinnabar,  &c.  Being  charg- 
ed with  the  proper  materials,  they  may  then  be  bedded  in  the 
sand-pot  (176),  and  surrounded  by  the  sand  to  a  height  more 
or  less  above  the  level  of  the  materials  within,  according  to 
the  volatility  of  the  substance.  A  red  heat  may  then  be  appli- 
ed, and  the  products  condensed  in  the  upper  part  of  the  flask; 
or  received  into  another  flask,  having  a  wide  neck  ;  or  with  the 
neck  cut  short  and  placed  over  the  first.  Sometimes  a  large 
tube,  with  its  end  bent,  so  as  to  pass  over  the  neck  of  the  flask, 
is  a  very  convenient  condensing  vessel.  The  joint  may  be 
wrapt  with  dry  paper,  and  tied  with  twine,  the  other  end  of 
the  tube  should  be  drawn  out  and  contracted  (1179),  so  as 
to  enter  a  globe,  in  which  vapours,  not  condensed  in  the 
tube,  may  be  caught  and  finally  rendered  solid. 

498.  When  Florence  flasks  can   be  heated  in  a  sand-pot, 
they  do  not  require  luting,  but  if  they  are  exposed  to  a 
naked  fire,  must  then  be  strengthened  by  an  exterior  coat  of 
clay  (1084). 

499.  Some  sublimations  are  most  conveniently  performed 
by  putting  the  substance  into  a  basin  (369),  which  is  then 
to  be  covered  with  another  containing  water;  the  applica- 
tion of  heat  to  the  lower  causes  the  evolution  of  vapours, 
which  are  condensed  against  the  bottom  of  the  upper.     Such 
sublimations  as  can  be  effected  by  the  heat  of  an  oil-lamp 
are  well  conducted  in  this  manner.     Sometimes  small  plati- 
num capsules  (371)  are  more  advantageous.     Indigo  is  best 
sublimed,  after  it  is  bruised,  by  being  put  in  small  quantities 
into  a  platinum  capsule  covered  by  a  larger  one  (371),  and 
the  lower  heated  strongly  by  a  spirit  lamp.     The  upper 
should  be  kept  at  about  212°;  or  a  little  below,  by  moisten- 
ing it  with  a  piece  of  wetted  bibulous  paper.     After  some 
time  the  sublimed  indigo  will  be  found  forming  a  layer  of 
crystals  upon  the  under  surface  of  the  upper  capsule. 

500.  Iron  and  earthen  crucibles  are  useful  for  the  sub- 
limation of  bodies  that  have  no  action  upon  them.     The 
crucible  may,  in  the  first  place,  be  charged,  and  after  being 
covered  by  a  large  vessel  to  condense  the  vapours,   heated 
in  a  sand-bath;  or,  being  previously  heated,  it  may  be  set 
upon  a  stone  or  brick,  and  after  the  substance  is  thrown  in, 


SUBLIMATION — RETOKT  NECKS IRON  POTS.  239 

it  may  be  covered.  Benzole  acid,  napthaline,  and  other 
such  bodies,  may  be  sublimed  from  them  into  proper 
vessels. 

501.  The  necks  of  broken  retorts  are  frequently  useful 
for  conducting  the  vapours  which  rise  during  sublimations 
in  crucibles,  &c.     They  are  conical,  and  occasionally  so 
large  at  the  retort  end,  that  they  easily  cover  a  small  cruci- 
ble standing  in  the  sand-bath.     The  sand,  if  heaped,  will 
often  serve  sufficiently  to  close  the  lower  end  of  this  con- 
ductor, and  the   upper,  being  introduced  into  a  flask  or 
globe,  conveys  the  vapours  into  them,  which  are  thus  re- 
moved so  far  from  the  source  of  heat  as  to  be  easily  con- 
densed. 

502.  Finally,  cast-iron  pots  (176)  are  sometimes  in  use 
for  the  purpose  of  effecting  sublimation  ;  but  they  require  to 
be  covered  with  a  head  and  tube,  for  the  purpose  of  leading 
the  vapours  to  a  vessel  sufficiently  large  to  receive  and  con- 
dense them  :  or  the  pot  being  so  set  as  to  have  a  level  sur- 
face continued  from  the  edges  on  all  sides,  a  box  or  large 
vessel  may  be  inverted  over  the  whole,  and  the  condensation 
effected  in  the  space  within. 

503.  It  is  much  to  be  regretted  that  the  chemist  cannot 
obtain  glass  retorts,  and  other  vessels  which  have  to  resist 
high  temperatures,  of  green  bottle-glass,  and  of  all  the  forms 
and  sizes  he  requires.     Large  glass  retorts,  for  the  purpose 
of  concentrating  sulphuric  acid  are  made  of  it,  and  some- 
times smaller  ones  may  be  obtained  :  but  an  abundant  va- 
riety, from  two  pints  to  an  ounce  in  capacity,  are  required 
in  the  laboratory  of  research.     Even  green  glass  tubes  are 
rarely  to  be  procured,  and  are  not  permitted  to  be  made 
without  the  special  leave  of  the  Board  of  Excise.     The  green 
glass  bottles,  retorts,  &c.,  that  are  frequently  met  with  in 
London,  are  either  flint  or  plate  glass,  neither  of  which 
have  the  hardness  and  difficult  fusibility  of  green  wine  bot- 
tle glass. 


240  PRECIPITATION ITS  OBJECTS 


SECTION  VIII. 

• 

PRECIPITATION. 

504.  PRECIPITATION  is  valuable  as  a  mode  of  separating 
substances,  and  consists  in  changing  them  from  a  soluble 
into  an  insoluble  state.  It  always  depends  upon  altering  the 
relation  of  the  solvent  to  the  substance  it  holds  in  solution  ; 
this  being  effected  sometimes  by  changing  the  state  of  the 
solvent,  as  when  water  is  added  to  a  solution  of  resin  in  al- 
cohol, or  alcohol  to  a  solution  of  gum  in  water  ;  and  at  other 
times  by  causing  a  change  in  the  body  dissolved,  as  when 
sulphuric  acid  is  added  to  a  'solution  of  baryta  to  precipitate 
the  earth,  or  ammonia  to  a  solution  of  iron  to  precipitate  the 
oxide.  It  is  often  practised  to  render  the  presence  of  a  sub- 
stance visible,  and  forms  an  essential  part  of  analytical  and 
other  processes,  as  well  in  the  discovery  of  bodies  (912, 
&,c.),  as  in  their  separation  and  estimation.  Any  substance 
added  to  a  solution  to  cause  a  separation  in  the  solid  form 
of  matters  present,  has  received  the  general  name  of  preci- 
pitant, and  the  substance  so  separated  is  called  a.  precipitate. 
505.  Many  of  the  vessels  useful  in  the  processes  of  preci- 
pitation have  been  already  described  as  glasses  (368),  basins 
(369),  and  flint-glass  and  Florence  flasks  (372,  373)  ;  but 
there  are  two  kinds  which  particularly  deserve  mention  here. 
The  one  is  a  small  cylindrical  glass  standing 
on  a,  foot,  about  one  inch  in  diameter  and 

two  and  a  half  in  height:  it  is  very  useful  in 

^=f     (^ >  *  j 

testing  mineral  waters  and  solutions  by  pre- 
cipitation, for  which  reason,  two  or  three  dozen  of  them 
should  be  in  the  laboratory  stock.  The  other  is  of  the  kind 
called  Phillips's  precipitating  glasses.  These  are  of  a  trun- 
cated conical  shape,  as  represented  in  the  wood-cut,  and  are 
peculiarly  useful  in  the  management  of  precipitates,  in  con- 
sequence of  the  facility  with  which  they  allow  the  solid  mat- 
ter to  fall  to  the  bottom  of  the  liquid.  The  precipitate,  as 
it  descends,  meets  with  no  obstruction  from  the  sides  of  the 


PRECIPITATION HELPS — THE  LIGHT.  241 

glass,  tending  indeed  rather  to  shrink  from  than  adhere  to 
it ;  the  fluid,  on  the  contrary,  tends  to  rise  in  the  space  left, 
and  thus  in  numerous  cases  great  facility  of  separation  is 
obtained.  They  should  be  provided  of  three  or  four  diffe- 
rent sizes,  having  about  the  capacity,  for  instance,  of  two, 
four,  and  eight  ounces  (118).  Jars  of  this  form  have  already 
been  described  (368). 

506.  When  in  the  progress  of  investigation  it  is  required 
to  know  whether  a  substance  in  solution  will  be  precipitated 
by  certain  tests,  the  latter  are  to  be  added,  and  the  whole 
purposely   mixed  or  suffered   to  become   so  spontaneously. 
If  immediate  separation  take  place,  the  question  is  answered; 
but  if  otherwise,  the  results  are  not  to  be  thrown  away,  and 
the  inquiry  decided  in  the  negative;   but  the  mixture  is  to 
be  allowed  to  stand  for  some  hours,  and   then  again  exam- 
ined.    If  no  appearance  of  precipitation  be  produced,  a  heat 
is  to  be  applied,  approaching  to  2 12°;  perhaps  precipitation 
may  occur  during  the  application  of  this  temperature,  and  if 
so,   the  point  is  ascertained  ;  but  if  not,  the  operator  must 
still   persist,  by  allowing  the   mixture  to  cool  to  common 
temperature,  and  then   observe  it  for  the   last  time.     For 
want  of  perseverance  of  this  kind,   possible  precipitations 
are  often  considered  as  impossible.     Dr  Wollaston's  test  of 
the  presence  of  potash  in  water  is  frequently  thought  to  be 
ineffectual,  merely  from  the  hasty  manner  in  which  the  ex- 
periment is  made. 

507.  Very  frequently   liquids  containing  precipitates  in 
such  small  quantities  as  merely   to  have   an  opalescent  or 
slightly  milky  appearance,  are  to  be  examined  and  perhaps 
compared  with   each  other  in  colour,  turbidness,  &c.     In 
these  cases  it  is  often  advantageous  to  examine   them  by 
reflected  light,  as  that  thrown  back  by  a  sheet  of  white  paper, 
for  which  purpose  the  glasses  containing  the  precipitates  may 
be  placed  on  white  paper,  or  at  other  times  a  piece  of  paper 
may  be  held  behind  them  at  an  angle  such  as  to  reflect  light 
from  the  sky-light  or  window.     The  tints  and  appearances  of 
several  glasses  in  a  row  are  very  Well  compared  with  each 
other  by  such  means,  and  the  process  is  often  of  value  in  com- 
parative testing. 

2  F 


242  PRECIPITATION — COMPLETION. 

508.  Precipitations  are  generally  effected  by  substances 
with    which    from    previous    experience,    they   are    known 
to  occur;  and  manipulative  instruction  merely  relates  to  the 
best  method  of  obtaining  those  expected    results,   and  of 
thus  securing  the  separation  of  the  whole  of  a  substance  held 
in  solution,  in  processes  instituted  for  its  purification,  or  for 
the  analysis  of  its  compounds.     It  is  to  be   understood  that 
these  operations  are  generally  best  performed  in  Phillips's, 
test-glasses  (505). 

509.  It  is  frequently  necessary  to  add  a  precipitant  to  a 
solution,  until  no  further  effect  is   produced.     Upon   com- 
mencing the  addition,  it  is  easy  to  observe  the  formation  of  the 
precipitate;  but  when  the  mixture  becomes  milky  or  thick, 
the  student  is  unable  to  perceive  whether  the  additions  he 
makes  actually  cause  increased  separation,  or  whether  they 
are  useless.     As  soon  as  this  happens,  it  is  better  to  desist 
from  adding  the  precipitant,  and,  after  stirring  the  whole  so 
as  to  mix  it  thoroughly,  to  allow  it  to  stand  a  few  minutes;  a 
separation  of  the  precipitate  from  the  liquid  will  take  place  at 
the  surface,  and  allow  the  removal  of  a  small  portion  of  the 
clean  fluid,  either  by  pouring  it  out  into  a  little  glass  (397), 
or  by  dipping  a  rod  into  it,  and  transferring  a  drop  or  two  to  a 
glass  plate  (70).     This  done,  a  small  quantity  of  the  preci- 
pitant is  to  be  .added  to  the  liquid  so  separated,  and  notice 
taken  whether  any  precipitate  is  produced;  if  not,  enough  has 
been  added  to  the  large  portion;  but  if  a  further  effect  takes 
place,  the  portion  removed  is  to  be  restored,  the  glass  or  valve 
being  washed  by  the  dropping-bottle  (402);  more  of  the  preci- 
pitant is  to  be  added,  and  the  whole  again  stirred  up  and  ex- 
amined as  before,  until   it  has  in  this  way  been  ascertained 
that  no  further  addition  will  produce  any  precipitation. 

5,10.  If  the  separation  of  the  precipitate  be  slow,  it  is  not 
necessary  at  all  times  to  wait  till  the  fluid  at  the  surface  be 
quite  clear;  for  when  opalescent,  the  further  effect  produced 
by  the  precipitant  in  the  trials  may  often  be  observed;  it  is 
only  when  approximating  to  a  sufficient  addition  of  the  pre- 
cipitant, that  perfect  clearness  in  the  portion  removed  is 
required.  When  the  precipitate  sinks  rapidly,  it  will  be  unne- 
cessary to  remove  any  portion  for  trial;  for  the  liquid,  being 


VASTY   PRECIPITATES.  243 

clear,  or  nearly  so,  to  the  depth  of  an  inch  or  two,  may  be 
tested  by  dipping  a  glass  rod  into  the  precipitant  and  bringing 
it  to  the  surface:  the  small  quantity  of  the  test  thus  conveyed 
will  show,  during  its  descent  through  the  clear  part,  whether 
more  is  required  or  not. 

511.  Sometimes  the  solution  contains  so  much  precipitable 
matter,  that  before  a  sufficiency  of  the  precipitant  has  been 
added,  the  whole  is  thick,  and  even  pasty.     In  nearly  all  such 
cases,  the  whole  ought  to  be  diluted  ;  for  not  only  is  the  fluid 
part  in  such  small  quantity,    when  compared   with  the  solid, 
as  to  be  inseparable   by  the  usual  means,  but  the  mixture 
cannot  be  made  with  such  facility  as  to  insure  uniformity 
in  every   part;  without  which,  uncertainty  with   respect  to 
the  addition  of  the  precipitant  will  be  occasioned.     But  if, 
from  peculiar  circumstances,  it  is  desirable  to  avoid  dilution, 
a  small  portion  of  the  mixture  must  be  diluted  in  a  little  glass, 
and  dried  as  before  :  the  quantity  of  water  thus  added  to  the 
general  mass,  when  the  portion  tried  is  returned,  will  be  no 
object. 

512.  The  precautions  just  given,  with  regard  to  the  undue 
addition  of  the  precipitant,  only  relate  to  those  cases  where 
either  an  exact  equivalent  to  the  substance  to  be  precipitated 
is  required,  or  the  precipitant  itself  is  valuable,  or  the  super- 
fluous addition  of  it  would  complicate  and  burden  the  solu- 
tion so  as  to  embarrass  future  operations.     If  a  peculiar  salt 
of  baryta  existed  in  solution,  and  it  were  required  to  obtain 
the  acid  pure  by  precipitating  the  earth  in  combination  with 
sulphuric  acid,  then  any  excess  of  the  latter,  above  the  ex- 
act quantity  necessary  to  neutralize  the  baryta,  would  re- 
main in  solution  and  contaminate  the  peculiar  acid  :  in  such 
a  case,  therefore,  the  precautions  above  described  must  be 
used,  and  it  is  better,   when  the  precise   point  required  is 
nearly  attained,  to  dilute  the  precipitant  (the  sulphuric  acid, 
in  this  instance),  so  that  less  risk  may  be  incurred  of  adding 
too  much  at  once. 

513.  If  the  object  be  merely  to  save  a  valuable  precipi- 
tant, as  nitrate  of  silver  when  used  for  muriatic  acid,  or  to 
keep  the  remaining  solution  as  free  from  extraneous  sub- 
stances as  possible,  then  the  trouble  of  very  delicate  testing, 


244  PRECIPITATION RAPIDLY  EFFECTED. 

as  before  described  (509),  may  be  of  more  consequence  than 
the  use  of  a  little  excess;  and  in  such  cases,  when  near  the 
point,  such  a  quantity  may  be  added  as  is  known  somewhat 
to  surpass  it.  But  when  the  precipitant  is  cheap,  does  no 
harm  if  added  in  excess,  and  when  none  of  the  points  above 
mentioned  require  attention,  it  is  better  not  to  lose  time  in 
minute  operations,  but  to  add  a  considerable  excess  at  once: 
and  indeed  in  many  experiments  it  will  be  found  that  this 
excess  is  either  necessary  for  the  perfect  separation  of  the 
substance,  or  advantageous  as  very  much  facilitating  it. 
The  student  who  is  commencing  his  experimental  operations 
should  in  all  cases  practise  the  method  directed  (though 
without  attending  to  great  exactness),  until  he  is  so  far  ac- 
quainted with  the  nature  of  the  ordinary  chemical  precipi- 
tants,  such  as  acids,  alkalies,  and  salts,  as  to  form  a  tolerably 
correct  notion  of  the  sufficiency  or  insufficiency  of  the  quan- 
tity added  by  the  appearances  it  produces. 

514.  Solutions  to  which  precipitants  have  been  added  are 
easily  mixed  in  glasses  or  small  jars,  by  agitating  with  the 
rods  or  stirrers  before  mentioned  (374)  ;  but  where  they  are 
bulky,  and  occupy  deep  vessels,  the  mixture  is  better  effected 
by  immersing  a  small  glass  tube  sufficiently  long  to  reach  the 
bottom  of  the  jar,  and  blowing  air  down  it  with  the  mouth, 
so  as  to  make  it  pass  through  the  fluid  in  bubbles.     These 
being  made  to  ascend  through  different  parts  of  the  solu- 
tion, the  whole  soon  becomes  uniformly  mixed.     The  ex- 
treme upper  end  of  the  tube  should  be  placed  quite  within 
the  mouth,  and  not  in  contact  with  the  lips,  tongue,  or  any 
other  parts;  so  that  nothing  but  air  or  aqueous  vapour  may 
pass  down  it*. 

515.  When  rods  or  tubes  are  used  to  stir  mixtures  which 
contain  weighed  or  valuable  substances,  the  adhering  fluid 
should  be  washed  off  into  the  vessel  by  the  dropping-bottle 
(402),  that  nothing  may    be    lost;  or,  if  required  several 
times,  they  may  in  the  intervals  be  placed  with  their  ends  in 
a  small  glass,  and  ultimately  both  glasses  and  stirrers  washed 
as  before  (509). 

*  Care  should  be  taken  not  to  use  this  method  of  agitating,  when  carbonic 
acid  gas  would  act  on  any  ot  the  substances  in  the  vessel.— ED. 


HEAT MOTION PECULIAR  PROCESSES.  24  "• 

516.  Precipitates  do  not  often  require  heat  for  their  for- 
mation and  separation,  but  in  particular  cases  it  is  very  ser- 
viceable :  basins   (369)   and  flasks   (372)  are   used  for  the 
purpose.     If  a  basin  is  to  be  used  for  the  application  of  heat, 
the  precipitate  may  be  thrown  down  in  it;  but  if  a  flask  is 
preferable,  the  precipitation  is  generally  better  effected  in  a 
glass  or  jar,  and  the  mixture  afterwards  transferred  to  the 
flask.     More  command  of  the  fluid,  and  easier  access  to  it, 
are  obtained  in  an  open  than  in  a  closed  vessel.     The  heat 
of  the  sand-bath  is  generally  sufficient  in  these  cases. 

517.  A  few  commonly-occurring  precipitates  are  affected 
by  peculiar  circumstances,  which  may   be  usefully  pointed 
out  in  this  place.     Chloride  of  silver,  continually  produced 
in  the  separation  of  muriatic  acid  or  chlorine  by  nitrate  of 
silver,  has,  when  abundant,  its  separation  facilitated  by  agi- 
tation.    When  the  liquid  containing  it  is  stirred,  or  poured 
backwards  and  forwards  from  one  vessel  into  another,  the 
chloride  adheres,  forming  heavy  flocculi,  which,  in  a  few  se- 
conds,  fall  to  the  bottom,  leaving  the  fluid  nearly  clear ; 
whereas,  without  such  agitation,  it  would  require  from  half 
an   hour  to   two  or  three  hours  to  produce   an  equal  effect. 
It  falls  also  more  readily  when  an  excess  of  the  nitrate  of 
silver,  «or  of  nitric  acid,  is  present;  for  which  reason  these 
substances  may  occasionally    be    added   with    advantage. 
Heat  assists  its  separation. 

518.  The  separation  of  sulphate  of  baryta  from  the  fluid 
containing  it,  is  very  much  facilitated  by  the  addition  of  a 
little  nitric  acid  in  excess  where  it  can  be  permitted  and  also 
by  heat.     The  two  together  are  highly  useful  in  many  ana- 
lytical processes. 

519.  Prussian  blue,  or  rather  the  blue  ferro-prussiate  of 
iron,  constantly  produced  in  testing  for  iron,  falls  much  more 
readily  in  solutions  containing  a  considerable  proportion  of 
salts  or  uncombined   acids,  thau  in  such  as  are  nearly  free 
from  them  :  and  for  this  reason,  the  addition  of  a  little  mu- 
riatic acid  is  often  advantageous.     When  recently  precipi- 
tated this  substance  is  soluble  in  pure  water. 

520.  The  oxide  of  tin,  formed  by  the  action  of  nitric  acid 
and  tin,  can  hardly  be  washed  with  pure  water,  because  of 


246          PRECIPITATION — CARBONATE   OF  LIME METALS. 

its  suspension  ;  but  a  little  common  salt  added  causes  it  to 
separate  easily,  and  may  be  used  in  cases  where  it  does  or 
can  do  no  injury. 

521.  Carbonate  of  lime,  when  thrown  down  from  a  solu- 
tion by  an  alkaline  carbonate,  has  a  loose  bulky  form,  which 
in  the  course  of  a  short  time  alters,  and  the  substance  be- 
.comes  a  fine  gritty  powder,  rapidly  settling  to  the  bottom  of 
'the  supernatant  fluid.     This  change,  which  is  advantageous 
to  the  separation  of  the  precipitate,  is  facilitated  by  the  ap- 
plication of  heat.     The  solution  from  which  the   lime  is  to 
be  precipitated  as  a  carbonate  should  not  have  much  acid  in 
excess,  for  then  much  carbonic  acid  is  evolved  upon  adding 
the  precipitant,  and,  if  cold,  much  carbonate  of  lime  at  first 
remains  in  solution.     The  application  of  heat  causes  the  se- 
paration of  this  portion,  but  then  a  large  part  of  it  adheres 
as  a  crust  to  the  vessel,  and  occasions  trouble  in  its  accurate 
separation.     For  this  reason  it  is  generally  better  to  add  al- 
kali in  the  first  place  to  neutralize  the  excess  of  acid,  and 
then  to  add  the  carbonate.     Ammonia  and  the  carbonate  of 
ammonia  are   the  substances   generally  preferred  for  the 
purpose. 

522.  Some  of  the  metals  are  now  and  then  precipitated 
from  their  solutions  in  the  metallic  state  by  other  metals. 
Thus  silver  is  thrown  down  by  copper,  copper  by  iron,  lead 
by  zinc,  &c.     In  these  cases  it  is  best  to  retain  the  solution 
in  an  acid  state  by  the  addition  of  a  little  excess  of  the  same 
acid  as  that  with  which  the  metal  is  combined.     Silver  is 
generally  precipitated  from  its  solution  in  nitric  acid.     The 
excess  of  nitric  acid  increases  the  rapidity  of  action,  in  con- 
sequence of  the  electrical  effect  which  occurs  as  soon  as  any 
silver  is  precipitated,  and  at  the  same  time  tends  to  prevent 
any  precipitation  of  copper  on  the  silver,  or  any  separation 
of  oxide  of  copper.     Copper  is  best  precipitated  by  iron  from 
its  solution  in  sulphuric  acid.     The  excess  of  that  acid  has 
scarcely  any  action  on  the  copper  once  precipitated,  and 
very   effectually  retains  all  the  iron  in  solution.     Lead  is 
readily  precipitated  by  zinc  from  any  of  its  soluble  salts  :  the 
excess  of  acid  is  not  so  necessary  in  this  case  ;  but  if  the  so- 
lution be  weak,  nitric  or  acetic  acid  is  still  advantageous. 


FILTRATION MATERIALS  FOR.  247 

523.  Dr  Wollaston  has  devised  a  very  beautiful  method  of 
precipitating  one  metal  by  another,  or  rather  by  two  others 
combined  into  a  voltaic  circuit.  This  process  will  be  de- 
scribed in  Section  xvii.,  on  Electricity  (1065). 


SECTION  IX. 

FILTRATION,   DECANTATION,    WASHING,    SEPA- 
RATION OF  FLUIDS. 

524.  FILTRATION  is  a  process  purely  mechanical.     From 
its  nature  it  can  only  be  effected  where  the  substances  to  be 
separated  are  such  as  will  not  dissolve  each  other;  and  in 
almost  all  cases  it  is  requisite  that  one  of  them  be  in  the 
fluid,  and  the  other  in  the  solid  state.     It  has  the  advantage 
of  requiring  no  chemical  change  in  the  bodies  to  which  it  is 
applicable.     It  is  of  extensive  service  in  chemical  research, 
and  is  often  supplementary  to  precipitation. 

525.  Filtration  is  a  process  analogous  in  its  nature  to  sift- 
ing, and  is  performed  by  putting  the  mixed  substances  into 
a  vessel  sufficiently  porous  to  admit  the  passage  of  one  sub- 
stance,  but  close  enough  to  retain  the  other.     As  before 
mentioned,  the  substances  to  be  separated  are  usually  fluids 
and  solids ;  hence  bodies  permeable  to  fluids  are  those  re- 
quired for   the  filter.     Unsized  paper,  cloth,  flannel,  tow, 
sponge,  sand,  pulverized  glass,  flints,  porous  stones,  earthen- 
ware, and  many  other  substances,  are  used  on  different  oc- 
casions ;  but  the  first  is  almost  exclusively  used  in  the  labo- 
ratory, a  few  of  the  others  now  and  then  being  resorted  to 
only  on  particular  occasions. 

526.  Funnels  are  continually  necessary   to  support   the 
paper   through    which    filtration  is     to  take    place.      The 
ordinary  funnels  required  in  the  laboratory  for  the  passage 
of  fluids  answer  the  purpose  very  well,  and  they  are  of  use 
for  supporting  filters,  when,  from  their  necks  being  broken 
off,  they  are  otherwise  unserviceable.     They  may  be  either 


248  FILTERING  PAPER  AND  STAND. 

of  glass,  or  good  Wedgwood,  or  other  earthenware;  those 
of  glass  are  to  be  preferred,  because  the  progress  of  the  fil- 
tration and  the  state  of  the  filter  can  be  better  ascertained 
in  them.  Metal  funnels  should  not  be  allowed  in  the  labo- 
ratory. 

527.  No  other  glass  vessels  than  the  precipitating  and 
test  glasses  (505),  and  the  jars  (368),  already  described,  are 
required.     Stirrers  will  be  necessary  ;  and  the  platinum  spa- 
tula, the  platinum-bladed  pocket-knife  (62),  and  sometimes 
other  spatulas,  are  very  useful  in  moving  precipitates. 

528.  The   funnels  containing  filters  may   frequently   be 
supported  by  the  glass  or  jar  intended  to  receive  the  filtered 
fluid,  and  at  other  times  by  the  rings  of  retort  stands.     But 
notwithstanding  these  facilities,  so  frequently  is  the  opera- 
tion required,  that  a  laboratory  should  be   supplied  with  at 
least  one  filtering  stand  of  considerable  size  (12).     The  end 

5 of  such  a  stand  is  represented  in  the 

F3  woodcut.      It  should  be    15  inches 

wide,  3  or  4  feet  long,  and  have  an 

interval  between  the  bottom  and  top 

of  12  inches.  The  top  should  have 
— —  a  number  of  round  holes  made  in  it 
at  intervals  of  6  inches,  differing  in  diameter  from  li  to  3 
inches  ;  two  or  three  small  ones  of  half  an  inch  or  an  inch 
in  diameter  being  intermixed.  The  whole  should  be  well 
made  and  firm,  so  as  to  support  considerable  weights ;  the 
top  having  frequently  to  answer  the  purpose  of  a  table,  and 
to  sustain  jars  full  of  solutions,  as  well  as  to  bear  funnels 
and  filters. 

529.  It  is  no  easy  matter  for  the  chemist  to  obtain  unob- 
jectionable filtering  paper  ;  arid  yet  it  is  of  such  importance 
in  reference  to  the  duties  it  has  to  perform,  that  he  should 
not  spare  pains  to  procure  the  best  possible.     It  should  be 
so  porous  as  to  admit  the  free  and  ready  passage  of  fluids; 
so  close  as  to  retain  the  finest  solid  particles  ;  so  strong  as 
to  bear  the  weight  of  a  considerable  quantity  of  fluid;  and 
so  pure  as  to  give  nothing  to  the  solution,  or,  if  heated  with 
the  substance  retained  upon  it,  to  occasion  no  mixture  of* 
ashes.     Some  chemists  use  plate-paper,  i.  e-,  the  paper  of 


FILTERING  PAPER  EXAMINED.  249 

copper-plate  printers.  It  is  very  porous,  and  yet  there  are 
few  precipitates  that  will  pass  through  it;  at  the  same  time 
it  is  often  tender,  generally  yields  a  considerable  quantity  of 
ashes  when  burnt,  and  is  inapplicable  for  minute  filters 
when  very  small  quantities  of  fluid  only  are  to  be  worked 
upon,  because  of  its  thickness  and  consequent  waste  of  the 
portion  of  solution  imbibed  by  it. 

530.  It  is  amongst  the  thinner  varieties  of  unsized  paper,  or 
white  blotting-paper,  kept  by  some  of  the  large  stationers, 
that  the  chemist  will  probably  find  the  kind  best  suited  to 
his  purpose.     It  should  be  so  strong,  that  a  single  filter  of 
it,  capacious  enough  to  hold   a  pint  of  water,  should  not 
break  with  that  quantity,  even  though  some  degree  of  agita- 
tion be  given  to  the  funnel  containing  it.     Its  porosity,  that 
is  to  say,  its  comparative  freedom  from  size  (for  all  is  sized 
in  a  slight  degree),  may  be  judged  of  by  holding  it  to  the 
tongue,  and  observing  how  it  absorbs  moisture ;  and  by  a 
cautious  pull  its  strength  may  be  ascertained  whilst  in  such 
moistened  state.     The  student  who  is  unused  to  the  exam- 
ination of  papers,  will,  however,  better  judge  of  its  capabili- 
ty of  allowing  fluid  to  pass,  by  actual  trial  with  water ;  a 
pint  filter,  filled  with  clean  water,  should  allow  the  fluid  to 
run  in  a  considerable  stream. 

531.  The  best  method  of  judging  of  the  purity  of  paper 
is  to  burn  it  and  examine  its  ashes  :  the  fewer  it  yields,  the 
better  is  it  adapted  for  filters.     A  demy  sheet  should  not 
yield  more  than  one  and  a  half  or  two  grains  of  ashes  alto- 
gether.    If  it  contains  more,  their  solubility  or  insolubility 
should  be  observed,  that  the  student  may  be  aware  of  the 
impurities  that  may  probably  be   imparted  to  solutions  in 
very  delicate  experiments.     In  minute  cases  of  investigation, 
sulphuric  acid  may  frequently  be  traced  to  the  sulphate  of 
lime  existing  in  the  filtering  paper. 

532.  Filtering  paper  should  be  cut  ready  for  use  into  dif- 
ferent sizes :  a  demy  paper  furnishes  useful  sizes  for  filters, 
when  the  sheet  is  separated  into  four,  or  six,  or  nine  parts; 
and   parcels   of  each  of  these   sizes    are    prepared ;  they 
should  have  a  string  passed  through  the  corners,  and  be  pre- 

2G 


250  F1LTUATION FILTERS PLAIN. 

served  for  use  in  a  clean  place.  This  previous  arrangement 
of  the  paper  is  very  convenient,  as  readily  supplying  the 
sizes  that  will  be  wanted,  and  in  preventing  the  waste  that 
would  occur  by  carelessly  tearing  up  a  sheet  each  time  a 
filter  is  required. 

533.  On  preparing  a  filter,  the  piece  of  paper  should  be 
first  examined,  bM  looking  through  it  against  the  light,  to 
ascertain  that  it  is  free  from  holes.     The  simplest  filter  is 
made  by  folding  the  paper  twice  in  opposite  directions,  in 
such  manner  as  to  bring  the  four  corners  together,  and  by 

opening  one  corner  from  the  other  three,  so 
as  to  produce  an  irregular  conical  cavity. 
Such  a  filter  being  put  into  a  funnel,  and  then 
filled  with  water,  will  immediately  permit  its 
passage :  but  from  the  similarity  of  form  be- 
tween the  filter  and  the  funnel,  and  the  close  adhesion  of  the 
former  to  the  latter,  over  by  far  the  greater  part  of  its  sur- 
face, considerable  obstruction  is  opposed  to  the  passage  of 
the  fluid,  and  the  operation  is  retarded.  For  this  reason 
different  contrivances  have  been  recommended,  to  separate 
the  filter  here  and  there  from  the  funnel,  and  allow  passages 
for  the  fluid.  Lavoisier  recommended  small  glass  rods  put 
into  the  funnel  before  the  filter  is  introduced,  so  as  to  lie 
down  and  against  the  sides.  Straws  are  used  in  a  similar 
way,  and  they  certainly  open  channels  in  their  immediate 
neighbourhood,  by  which  the  fluid  may  flow.  By  other 
chemists,  ribbed  funnels  are  recommended  ;  but  it  is  difficult 
to  find  a  funnel  so  deeply  ribbed  as  to  support  the  paper  in 
such  a  manner  that  it  shall  not  touch  the  glass  in  every  part; 
and  if  they  do  not  perform  this,  they  are  of  no  use. 

534.  The  best  expedient  by  far  is,  to  fold  the  filter  in  such 
a  manner  that  ribs  may  exist  in  the  paper  itself;  and  this 
may  be  done,  so  as  not  only  to  allow  numerous  free  passages 
for  the  fluid  between  the  filter  and  the  glass,  but  also  to  al- 
low of  ready  transmission  through  its  whole  surface,  and  not 
of  one-half  only  and  even  that  imperfectly,  as  in  the  former 
case  (533).     For  this  purpose,  the  paper  is  first  to  be  doubled 
and  in  this  state  is  again  to  be  folded  in  half,  each  half  folded 
into  quarters,  and  each  quarter  into  eighths,  the  folds  being 


FILTRATION — FOLDED  FILTERS.  251 

all  on  the  same  side,  and  radiating  at  equal  distances  from 
the  middle  of  the  folded  edge  to  the  other  edges.     The 
woodcut  represents  the  doubled  paper  thus 
divided  into  eight  parts.     Each  eighth  is 
now  to  be  divided  into  half  by  folds  in  the 
opposite  direction,  but  in  lines  still   origi- 
nating at  the  same  centre,  which  makes  th4|doubled  piece  re- 
semble a  child's  paper  fan,  both   when  closed   and  when  a 
little  open  :  it  is  represented   by   the  ac. 
companying  figure.     Whilst  in  this  state, 
the  projecting  corners  should  be  taken  off 
by  a  knife  ;  folding  the  whole  up  tight  like 
a  closed  fan,  and  making  the  section  at 
about  a.     Being  now  allowed  to  expand  a 
little,  the  originally  doubled  sides  are  to  be  separated  from 
each   other  for  the  first  time,  but  without  disturbing   the 
angles  or  bending  the  ridges  or  ribs  formed  in  them.     Hav- 
ing opened  it  sufficiently  to  separate  the  cut  edges  from 
each  other,  it  will  be  found  that  the  paper  is  equally  divi- 
ded into  parts  forming  alternate  external  and  re-entering 
angles,  except  at  the  two  edges  b  5,  where  two  external 
angles  come  together.     Here  the  intervening  portion  of  pa- 
per between  the  two  contiguous  external  angles  should  be 
folded,  by  bringing  the  latter  together  and  creasing  the  pa- 
per down,  so  as  to  form  a  re-entering  angle  between  them  : 
this  should  be  done  at  both  places.     Then, 
opening  the  paper  sufficiently  to  bring  the 
bottom  into  proper  shape,  by  thrusting  out 
the  part   which  is  convex  within,  so  as   to 
make  it  project  externally,  the  filter  is  com- 
pleted, and,  being  put  into  a  funnel,  is  ready 
for  use.     Its  appearance,  when  perfectly  formed,  is  repre- 
sented by  the  accompanying  woodcut. 

535.  It  is  necessary,  in  making  these  filters,  that  the  folds 
be  not  continued  to  the  point,  but  that  they  should  stop 
about  half  an  inch  short  of  it  (see  the  last  figure),  for  if 
completed  to  the  bottom,  the  frequent  action  of  the  fingers 
in  folding  will  so  far  break  down  and  destroy  the  texture  of 


e    252  FILTRATION FILTERS. 

that  part,  that  a  hole  probably  will  appear  before  the  filter 
is  finished  ;  or  if  not,  it  will  be  so  weakened  as  to  be  unable 
to  bear  a  quantity  of  fluid  without  breaking.  Hence  that 
part  of  the  filter  will,  during  the  folding,  assume  a  concave 
form;  and  the  regularity  of  the  folds,  which  by  practice 
may  be  easily  attained,  must  be  strictly  attended  to  in  the 
upper  part,  but  may  be  dispensed  with  at  the  lower.  When 
opened  out,  therefore,  for  the  completion  of  that  part,  be- 
fore the  filter  is  put  into  the  funnel,  all  that  will  be  required 
is  to  push  that  side  of  the  bottom  outwards  which  is  convex 
inwards,  doing  it  so  carefully  as  to  cause  no  injury.  The 
folds  of  the  filter  should  be  distinct  and  sharp — an  effect 
which  should  be  obtained  by  a  single  decisive  pressure,  and 
not  by  much  fingering.  No  wrinkle  or  mark  should  appear 
in  the  well-made  filter  except  the  folds  described,  and  the 
portion  of  paper  between  the  folds  should  be  as  stiff  as  when 
first  taken  up.  The  filter  should  be  handled  lightly  during 
the  whole  of  the  operation,  and  never  be  opened  out  more 
than  is  represented  in  the  last  figure.  It  is  best  to  keep  the 
folds  as  close,  and  the  whole  filter  as  compact,  as  possible ; 
dropping  it  loosely  into  the  funnel,  and  permitting  the  fluid 
poured  in  to  do  the  office  of  opening  it  out.  It  should  be 
so  regularly  made,  that,  when  thus  expanded  by  the  fluid, 
the  external  angles  of  the  folds  should  touch  the  glass  at 
equal  distances  from  each  other,  except  at  two  opposite 
places  where  smaller  divisions  exist ;  and  unless  a  large 
quantity  of  fluid  be  present,  the  angles  at  the  upper  part 
should  remain  nearly  as  sharp  when  the  liquid  is  introduced, 
as  they  were  before.  Below,  they  gradually  pass  into  the 
rounded  surface  forming  the  centre  or  bottom  of  the  filter, 
which  will  be  about  the  size  of  a  sixpence  or  shilling,  ac- 
cording to  the  dimension  of  the  funnel  in  that  part.  These 
filters  leave  such  free  space  between  themselves  and  the 
glass  as  to  admit  of  the  passage  of  fluid  to  a  far  greater  ex- 
tent than  is  necessary ;  and  no  obstruction  being  placed 
against  the  external  surface  of  the  paper,  the  whole  acts  in 
the  filtration,  and  that  in  the  most  favourable  manner. 

536.  Of  these  two  kinds  of  filters,  which  may   be  distin- 
guished as  the  plain  and  the  folded,  sometimes  the  one  and 


FILTERS   APPLIED.  253 

sometimes  the  other  is  preferable.  When  the  object  is  to 
cleanse  and  purify  the  fluid,  that  being  the  valuable  part,  it 
is  most  rapidly  and  effectually  attained  by  a  folded  filter; 
but  when  the  precipitate  is  the  part  required  to  be  taken 
care  of,  it  is  generally  desirable  not  to  spread  it  over  the  ir- 
regular and  extensive  surface  of  such  a  filter,  but,  by  using 
a  plain  one,  to  retain  it  on  a  surface  of  only  half  the  extent. 
It  is  then  likewise  of  such  uniform  thickness  in  every  part, 
as  best  to  admit  of  the  operation  of  washing,  by  having  suc- 
cessive portions  of  water  passed  through  it ;  and  when  the 
filter  is  opened  out,  the  precipitate  is  delivered  in  one  con- 
tinuous portion,  and  not  divided  into  many  parts,  as  happens 
with  the  folded  filter. 

537.  When  a  single  filter  is  judged  too  weak  to  hold  the 
mass  of  fluid  it  is  required   to  sustain,  a  double  one   should 
be  used.     If  the  filter  is  to  be  a  folded  one,  then  a  double 
thickness  of  paper  is  to  be  taken  ;  but  if  plain  filters  are 
used,  the  two  should  be  made  separately,  and  put  one  into 
the  other,  in   such   a   manner  that    the    three    thicknesses 
of  the  one  may   come  against  the  single  thickness  of  the 
other.     Occasionally  it  is  proper  to  strengthen  the  bottom 
of  the  filter,  which,  not  being  supported  by  the  glass,  has  to 
support  the  greatest  column  of  fluid,  but  not  so  as  to  ob- 
struct the  upper  part,  where  a  filtration  as  free  as  possible 
is  required.     In  such  a  case-a  smaller  filter  is  to  be  added 
to  the  exterior  of  the  large  one,  so  that  it  may  not  interfere 
with  the  precipitate  within,  when  it  is  necessary  to  remove 
it  from  the  paper. 

538.  When   the  substance  collected  upon  a  filter  is  such 
that  heat  can  do  it  no  harm,  and  that  therefore  it  is  resolved 
to  burn  the  filter  for  the  sake  of  procuring  all  the  substance, 
then  use  a  double  filter,  the  inner  one  on  which  the  precipi- 
tate is  disposed  being  of  India-paper. 

539.  The  filter  and  funnel  being  ready,  and  placed  on  the 
stand  in  one  of  the  holes  before  mentioned  (528),  over  a 
glass  ready  to  receive  the  liquid,  the  mixture  to  be  filtered 
is  to  be  introduced.     It  should  not  be  poured  from  a  great 
height,  nor  upon  the  middle  of  the  filter,  but  down  the  side, 
the  force  of  its  descent  being  diminished  as  much  as  possible 


254  WASHING  A   PRECIPITATE. 

•?'. 

by  good  management,  lest  it  break  a  hole  through  the  pa- 
per:  for  the  same  reason  it  is  better  to  pour  it  down  the 
rod  (369).  If  the  first  portions  of  fluid  which  pass  be  not 
clear,  they  should  be  returned  into  the  filter,  and  a  second 
glass  be  placed  beneath  ;  the  solid  matter  in  the  liquor  to 
be  filtered  will  soon,  by  adhering  against  the  paper,  cause 
clear  filtration,  except  perhaps  in  one  or  two  particular 
cases,  as  with  precipitated  oxide  of  tin,  &c.,  on  which  occa- 
sions a  double  thickness  of  paper  must  be  used.  On  chang- 
_  ing  the  vessels  beneath  the  filter,  for  the  removal  of  the 
clear  solution,  it  should  be  done  so  that  no  drop  be  lost. 
By  inclining  the  empty  vessel,  its  edge  may  be  brought  un- 
der the  funnel  before  the  full  one  is  removed;  and  in  no 
case  should  a  vessel  be  left  under  the  filter,  in  which  there 
is  not  sufficient  room  for  the  contents  of  the  latter  if  it  should 
break.  Such  an  accident  ought  not  to  occur,  but  ought  al- 
ways to  be  provided  against. 

540.  Supposing  a  precipitated  substance  is  to  be  filtered 
from  the  solution  containing  it,  and  then  washed,  the  mix- 
ture may  be  poured  in  all  at  once,  or  added  successively. 
In  the  former  case,  as  the  fluid  passes  through,  the  precipi- 
tate forms  a  soft  mass  lying  upon  the  paper,  but  hollow  in 
the  middle  ;  in   the   latter,  this   hollow   nearly  disappears, 
from  the  successive  portions  of  solid   matter  added.     The 
first  state  is  the  most  advantageous  for  the  operation  of 
washing,  when  it  is  necessary  for  the  removal  of  the  portion 
of  solution  retained  by  the  mass  on  the  filter.     For  this  pur- 
pose the  vacant  space  should  be  filled   with   water,  that  it 
may  pass  through  and  displace  the  solution  ;  and  this  should 
be  done  before  the  part  within  has  drained  to  the  utmost, 
and  whilst  it  is  still  soft  and  bulky,  for  the  water  then  finds 
easier  access  to  all  its  parts.     This  water  having  passed,  a 
second  and  third  portion  should  be  added,  and  the  washing 
thus  repeated,  until,  by  testing  the  liquid  which  passes,  it  is 
found  to  be  perfectly  pure,  or  to  contain  so  little  matter  as 
to  render  the  rest  unimportant. 

541.  Sometimes  the  mass,  though  light,  is  adhesive:  it 
may  then  very  advantageously  be  stirred  up  with  the  added 
water,  but  great  care  must  be  taken   that  the   filter  be  not 


WASHING  FILTERS.  255 

broken  in  the  operation.  The  top  of  a  quill  feather  may  be 
used  for  the  purpose.  At  other  times  as  much  fluid  as  pos- 
sible having  passed  through,  the  filter  with  its  contents  may 
be  put  into  a  fresh  portion  of  water,  the  paper  removed,  and 
the  precipitate  being  stirred  up  with  the  water,  the  whole 
may  be  put  upon  a  new  filter.  These  processes  are  applica- 
ble when  a  quantity  either  of  the  substance  in  solution  or  of 
the  precipitate,  being  required  in  a  pure  stale,  it  is  desirable 
to  avoid  loss  as  much  as  possible,  without  being  particularly 
accurate.  The  student  should  understand,  that  when  a  pre- 
cipitate in  its  moist  state  occupies  a  large  portion  of  the 
space  within  a  filter,  it  is  impossible,  except  in  very  long 
periods  of  time,  to  wash  it  perfectly  merely  by  passing  water 
through  it,  because  of  the  greater  facility  of  passage  which 
the  water  will  find  in  one  direction  rather  than  another. 
When  the  precipitate  forms  but  a  thin  layer,  or  when  it  can 
be  completely  stirred  -up  from  the  bottom  by  a  jet  of  water 
(403,  547),  or  a  feather  it  may  be  well  and  perfectly  washed. 

542.  It  is  advisable   in  all  cases  of  washing  in  filters, 
where  accuracy  is  necessary,  to  make  the  filter  of  such  a  size 
as  to  drop  entirely  within  the  funnel,  and  to  cover  the  latter 
with  a  clean  basin.     This  protects  the  upper  moistened  parts 
of  the  filter  from  evaporation,  which  would  cause  the  slow 
but  continual  ascent  of  portions  of  the  fluid  from  below,  and 
consequently  a  deposit  of  the  substance  there.     In  slow  fil- 
trations  a  considerable  quantity  of  the  substance  in  solution 
would  be  accumulated  in  the  upper  part  of  the  filter,  instead 
of  being  washed  away. 

543.  It  is  necessary,  in  certain  cases,  first  to  moisten  the 
filter  with   water.      When  aqueous  solutions  of  vegetable 
matter,  which  are  thick  and  adhesive,  are  to  be  cleansed  by 
this  process,  the  filter  should  be  thus  prepared.     The  advan- 
tage will  be  found  very  considerablq^ith  solutions  of  sugar. 
In  the  filtration  of  alcoholic  vegetaDle  solutions,  the  filter 
should  always   be  previously  moistened  with  pure  alcohol. 
Fixed  or  essential  oils,  or  naphtha,  and  similar  bodies,  in 
mixture  with  water  or  aqueous  solutions,  in  which  they  are 
not  soluble,  may  be  separated  from  the  latter  by  a  paper  fil- 
ter, previously  moistened  with   pure  water.     In  some  few 


256 


HOT  FILTRATION HARE7S  METHOD. 


cases  the  other  substance  may  be  made  to  separate  by  passing 
through  the  paper,  the  filter  having  been  previously  im- 
bued with  a  portion  of  it  in  a  state  of  purity. 

544.  Sometimes  hot  filtrations  are  to  be  performed.     Oils 
filter  better  hot  than  cold  :  tallow  and  cocoa-nut  oil  may  be 
passed  through  paper  when  hot ;  and  many  solutions  must  be 
filtered  at  high  temperatures,  because  of  the  greater  solu- 
bility of  the  ingredients  under  those  circumstances.     In  these 
cases  the  fluids  should  be  heated  in  a  flask  or  basin  before 
they  are  poured  into  the  filters ;  and  the  filter-funnels  being 
placed  in  the  glasses  or  jars,  and,  after  the  fluid  is  poured 
in,  covered  over  with  a  basin  or  glass  plate,  the  whole  should 
be  enveloped  in  a  piece  of  flannel  or  a  dry  cloth.     If,  from 
the  length  of  the  operation  or  other  causes,  the  flannel  or 
cloth  be  not  efficient,  it  may  be  dispensed  with  ;  and  the  glass 
and  filter,  being  placed  on  a  warm  part  of  the  sand-bath, 
should  be  covered  with  a  box  or  vessel  large  enough  to  rest 
on  the  sand,  and  thus  form  a  hot-air-chamber  for  the  process. 
When  the  operations  are  upon  a  small  scale,  a  paper  cone 
(1343)  is  sufficient  to  cover  the  vessels  on  the  sand-bath  and 
keep  them  hot.     These  filtrations  may  very  often  be  con- 
ducted with  great  facility  by  means  of  a  current  of  hot  air 
directed  against  the  vessels  (269). 

[The  figure  represents 
Dr  Hare's  instrument  for 
filtering  liquids  which 
require  to  be  kept  hot 
during  the  process.  It  is 
a  tin  case  penetrated  ver- 
tically by  two  cones;  one 
erect,  the  other  inverted. 
Through  the  inverted 
cone  maybe  passed  a  glass 
funnel  j  and  under  the 
other  is  placed  a  lamp  by 
which  the  temperature  of 
water  inclosed  in  the  case 
may  be  sustained. — ED.] 

545.  In  filtrations  of  alcohol,  or  alcoholic  solutions,  the 


FILTRATION SMALL  FiLTEUS.  257 

funnel  should  be  put  into  the  glass,  and  covered  as  before 
mentioned  (542),  that  evaporation  maybe  prevented  as  much 
as  possible.  In  all  filtrations  for  analysis  the  filter  should  be 
coverej  in  the  same  manner,  to  prevent  accumulation  of  sub- 
stances in  the  upper  part  of  the  paper.  These  covers  should 
in  no  case  touch  the  filter,  but  merely  rest  upon  the  edges 
of  the  funnels. 

546.  When  working  upon  minute  quantities,  filters  as 
small  as  possible  are  used,  that  but  little  of  the  fluid  may  be 
absorbed.  When  of  such  size  as  will  result  from  a  piece  of 
paper  three  inches  square  o'r  less,  they  are  better  not  folded, 
but  plain  (533,  536),  and  may  then  be  supported  without  a 
funnel  upon  the  mouth  of  a  small  test-glass  (505).  When  a 
lipped  Phillip's  test-glass  is  to  be  used,  nothing  more  is  re- 
quired than  to  select  one  having  a  diameter  at  the  mouth  of 
about  one  inch  and  a  quarter,  or  less,  according  to  the  size 
of  the  filter;  from  one  half  to  a  third  of  which,  when  in  its 
place,  is  to  be  left  above  the  edge  of  the  glass.  In  arrang- 
ing the  filter,  the  triple  or  stronger  side  should  be  placed 
opposite  the  lip,  that  the  form  may  be  retained,  and  the  space 
at  the  lip  left  open  for  the  passage  of  air 
outwards,  as  the  fluid  passes  into  the  vessel. 
These  filters  should  never  be  filled  to  a 
height  much  above  the  edge  of  the  glass, 
•otherwise  the  weight  will  sometimes  bend  the  paper  over  the 
outside,  and  derange  the  whole.  If  the  glass  used  has  no 
lip,  then  a  double  fold  must  be  made  in  the  single  side  of  the 
filter,  so  as  to  make  a  portion  from  the  top  to  nearly  the  bot- 
tom project  inwards  and  appear  like  a  sharp  ridge.  When 
put  into  the  jar,  this  will  form  a  notch  as  it  were  in  the  side 
of  the  filter,  by  which  the  air  may  find  a  passage  outwards. 
It  is  necessary  in  these  small  filtrations  that  the  air-passage 
be  attended  to  and  kept  open  ;  should  it  be  badly  formed, 
or,  from  the  quantity  of  fluid  within,  be  pressed  against  the 
glass,  or  stopped  up  by  the  abundance  of  liquid  which  passes 
through  the  filter,  either  filtration  will  cease,  or  the  fluid,  not 
being  able  to  enter  the  glass,  will  flow  over  and  down  the 
outside,  and  be  lost. 

547.  The  dropping-bottles  (402)  will  be  very  useful  in  all 

2  H 


258  FILTRATION — VARIETIES. 

these  filtrations,  especially  those  on  a  minute  scale ;  and  there 
is  another  bottle,  recommended  by  Berzelius,  which  is  also 
useful.  It  is  formed  much  like  the  dropping-bottle,  but  the 
cork  has  no  notch  in  the  side,  being  inserted  air-tigty,  and 
the  glass  tube  has  a  small  aperture.  When  about  half  or 
two-thirds  filled  with  water,  it  is  to  be  inverted,  and  then,  by 
applying  the  mouth  to  the  aperture,  air  is  to  be  forced  in 
through  the  tube  and  water,  and  condensed  as  much  as  pos- 
sible in  the  upper  part :  when  the  mouth  is  removed,  this 
compressed  air  forces  out  the  water  in  a  small  stream,  which 
continues  for  some  time,  and  which,  directed  against  the  sides 
of  the  filter,  washes  the  precipitate  from  the  paper,  and  ac- 
cumulates it  at  the  bottom.  It  is  necessary  in  many  cases  to 
collect  the  precipitate  at  the  bottom  of  the  filter  as  much  as 
possible ;  and,  for  this  purpose,  besides  the  dropping-bottle 
anjd  Berzelius's  bottle,  a  syringe  (560)  may  also  be  employed. 
This  instrument  is  easily  made  from  a  piece  of  glass  tube  at 
the  blow-pipe  table  (1181),  and  is  very  effectual  in  cleansing 
the  sides  of  the  filter. 

548.  When  a  filter  is  required  so  large  that  paper  alone 
has  not  strength  sufficient,  a  piece  of  cloth  should  be  fastened 
by  the  edges  to  a  slight  square  frame  of  wood,  so  thatit  may 
hang  loosely  ;  a  sheet  of  filtering  paper  should  be  laid  over 
it,  and  the  fluid  to  be  filtered  placed  upon  that. 

549.  When  the  object  is  hastily  to  filter  a  fluid  for  the 
purpose  of  removing  pieces  of  dirt,  then  a  little  loose  tow  at 
the  bottom  of  the  funnel,  or  apiece  of  sponge  slightly  thrust 
in,  is  often  sufficient  for  the  purpose.     Upon  some  few  oc- 
casions filters  for  acids  are  required.     These  are  generally 
recommended  of  powdered  glass,  being  arranged  somewhat 
in  the  manner  described  for  lixiviation   (420).     Pieces  of 
glass  are  put  into  the  neck  of  the  funnel ;  upon  these  smal- 
ler fragments,  then  again  other  layers  of  particles  diminish- 
ing in  size,  until  a  moderately  fine  powder  has  been  used, 
the  top  being  finished  by  a  layer  of  small  fragments,  to  pre- 
vent disturbance  by  pouring.     The  pieces  of  glass  should  be 
well  cleaned  before  pulverization,  and,  when  arranged,  some 
water  should  be  passed  through  the  filter,  to  remove  alkali 
or  other  matters  that  may  be  separable  from  the  glass,  which 
should  be  that  of  wine-bottles,  and  not  flint  glass* 


DECANTATION SYPHON.  259 

Another  mode  of  separating  a  fluid  from  the  finely-divided 
solid  matter  it  may  contain,  is  to  aljow  the  latter  to  deposit, 
and  then  to  remove  the  former.  This  is  called  decantation; 
it  is  a  process  much  superior  to  filtration  in  many  analytical 
experiments,  and  recommended  in  preference  both  by  Lavoi- 
sier and  Berzelius. 

550.  If  the  fluid  be  poured  off,  it  should  be  done  from  a 
lipped  jar  (368,  397),  and  with  a  very  steady  hand,  that  as 
much  may  be  removed  as  possible,  before  the  deposit  at  the 
bottom  be  disturbed.     But  a  better  method  by  far 
is,  to  use  a  syphon.     Let  a  piece  of  glass  tube,  about 
0.3  of  an  inch  internal  diameter,  22  inches  in  length, 
and  of  sufficient  thickness  to  bear  ordinary  labora- 
tory work,  be  bent  at  the  blow-pipe  table,  so  that  one 
limb  shall  be  about  two  inches  longer  than  the  other; 
jthe  extremities  should  be  contracted  at  the  lamp 
(1166,  1175),  until  about  0.2  of  an  inch  in  diameter. 
So  formed,  when  filled  with  fluid  and  held  as  in  the  figure, 
but  with  one  aperture  closed  by  a  finger,  the  fluid  will  not 
fall  out  at  the  other,  because  of  its  smallness;  and  yet  the 
larger  diameter  of  the  body  of  the  syphon  will  permit  a  more 
rapid  passage  of  fluid  than  would  otherwise  take  place. 
When  this  instrument  is  to  be  used  to  separate  the  liquid  in 
a  jar  from  the  deposit  lying  at  the  bottom,  the  syphon  is  to 
be  inverted  and  inclined,  so  that  the  orifice  of  the  shorter 
leg  shall  be  higher  than  the  other  :  it  is  then  to  be  filled  with 
water  from  the  dropping-bottle,  taking  care  that  no  bubbles 
of  air  are  included,  which  is  easily  done  by  holding  the  beak 
of  the  bottle  against  the  side  of  the'aperture  ;  and  when  the 
water  has  filled  the  longer  leg  it  is  to  be  closed  by  a  finger, 
and  more  water  added  till  the  other  leg  also  is  full.     Keep- 
ing the  finger  tight  upon  the  orifice  that  no  air  may  enter  it, 
the  syphon  is  to  be  inverted,  so  as  to  bring  it  into  its  acting 
position  ;  the  shorter  leg  is  to  be  introduced  into  the  fluid  ; 
and  then,  by  withdrawing  the  finger,  the  fluid  is  to  be  suf- 
fered to  run  out  into  a  vessel  placed  to  receive  it. 

551.  The  current  may  at  any  time  be  diminished,  or  pre- 
vented altogether,  by  applying  the  finger  partly,  or  closely, 
against  the  exterior  aperture,  and  thus  complete  command 


260  RECANTATION SYPHON. 

in  that  respect  be  obtained.  As  the  surface  of  the  fluid  de- 
scends in  the  jar  and  approaches  the  sediment,  care  must  be 
taken  that  the  immersed  end  of  the  syphon  be  not  brought 
so  near  the  deposit  as  to  cause  any  disturbance  of  it;  and 
towards  the  last,  by  diminishing  the  'current  and  inclining 
the  jar  very  slowly  and  steadily,  the  endeavour  should  be  to 
remove  as  much  clear  fluid  as  possible,  without  drawing 
away  any  of  the  precipitate.  This  may  be  done,  so  that  not 
above  a  cubic  inch  of  clear  fluid  need  be  left  behind.  The 
syphon  is  best  held  in  the  right  hand  during  the  operation, 
at  about  the  middle  of  the  exterior  leg.  A  degree  of  gov- 
ernment over  the  current  may  be  obtained  by  inclining  the 
syphon,  so  as  to  bring  the  aperture  of  the  external  leg  nearly 
to  a  level  with  the  surface  of  the  fluid  in  the  jar,  but  in  all 
cases  it  should  be  kept  somewhat  below  the  latter.  The  jar 
should  be  placed  in  a  steady  position  during  the  operation, 
and  it  is  proper  to  raise  it  till  nearly  on  a  level  with  the  eye. 
The  top  of  the  filtering  stand '(528,  12)  answers  very  well  for 
these  occasions. 

552.  When  a  very  deeply-coloured  solution  is  to  be  drawn 
off,  so  dark  indeed  as  to  hide  the  end  of  the  syphon  when  in 
the  middle  of  the  fluid,  that  end  should  be  brought  close  to 
the  side  of  the  glass,  and  a  lighted  candle  held  on  the  out- 
side near  it ;  in  this  way  the   precipitate,  the  depth   of  the 
clear  part,  and  the  orifice  of  the  syphon  may  be  seen,  when 
they  cannot  be  observed  by  any  other  means. 

553.  Washing  by  decantation  is  much  more  easily  and  ef- 
fectually performed  than  by  filtration,  but  it  requires  more 
water,  and  hence  one  great  use  of  a  plentiful  supply  of  dis- 
tilled water  (36)  in  the  laboratory.     After  having  drawn  off 
the  clear  solution,  it  is  merely  necessary  that  the  jar  be 
filled  up  with  water,  the  whole  mixed  either  by  a  stirrer  or 
by  blowing  (514),  the  mixture  left  to  settle,  the  clear  fluid 
decanted,  and  fresh  water  added  ;  the  operation  is  to  be  re- 
peated until  what  is  removed  contains  no  soluble  matter. 
Phillip's  test  glasses  (505)  and  jars  (368)  are  very  useful  in 
these  washings,  because  of  the  facility  with   which  the  pre- 
cipitate falls  in  them  to  the  bottom.     Some  solid  substances 
contract  into  a  smaller  space  than  others,  but  even  the  most 


DECANTATION WASHING.  261 

bulky  should  have  so  much  water  added  to  them,  as  to  ena- 
ble five-sixths  to  be  drawn  off  after  twelve  hours  standing. 
During  the  time  the  deposition  is  taking  place,  the  glasses 
or  jars  should  be  covered  to  keep  out  the  dirt.  The  bot- 
toms of  footed  glasses  (368,  1222)  answer  this  and  many 
other  useful  purposes ;  when,  therefore,  such  glasses  are 
broken,  the  upper  part  should  be  chipped  away,  and  the 
bottoms  reserved  in  a  drawer. 

554.  When  the  substance  has  been  sufficiently  washed, 
and  is  left  with  as  little  fluid  upon  it  as  possible,  it  may,  ac- 
cording to  the  requisite  circumstances  of  the  case,  be  pour- 
ed into  a  basin  and  evaporated  (as  will   be  described  in 
Section  xi.  590,  &c.),  or  poured  into  a  filter  to  remove  more 
of  the  fluid,  or  the  water  maybe  removed  by  means  of  bibu- 
lous paper.     There  are  many  bodies,  such  as  chloride  of 
silver,  oxide  of  copper,  carbonate  of  lime,  sulphate  of  baryta, 
and  others,  which  readily  fall  in  water  and  occupy   but  a 
small  space  ;  and  which,  having  been  washed,  are  best  freed 
from  the  remaining  water  in  the  latter  method.     For  this 
purpose  they  should  be  transferred  carefully  into  a  small 
evaporating  basin,  using  the  dropping-bottle  for  washing  in 
the  last  portions  (402,  547),  and  allowed  to  settle  to  the 
bottom,  an  effect  which  is  accelerated  by  moderate  warmth  5 
thea  folding  up  a  piece  of  filtering  paper  two  or  three  times, 
its  end  should  be  applied  cautiously  %  the  surface  and 
suffered  to  imbibe  part  of  the  water ;  this  done,  it  must  be 
taken  out,  the  wet  end  pulled  off,  and  the  edge  again  intro- 
duced,  as  in  a  process  formerly  described  (69),  observing 
that  no  solid  matter  be  disturbed  during  the  operation.     By 
taking  the  precautions  formerly  given  (69) ;  by  inclining 
the  basin  a  little;  and  by  similar  attentions,  which  will  sug- 
gest themselves  at  the  moment,  nearly  the  whole  of  the  wa- 
ter may  in  this  way  be  removed  without  disturbing  the  sub- 
stance. 

555.  The  formation  of  a  syphon  by  a  few  threads  of  mois- 
tened cotton,  or  by  a  piece  of  folded  and  bent  filtering  pa- 
per, is  now  and  then  very  convenient  for  the  gradual  separa- 
tion of  a  fluid.     If  a  basin  contain  a  mixture  of  fluid  and 
solid  matter,  and  the  cotton  or  the  piece  of  paper  be  bent 


262  TEMPORARY  SYPHON SEPARATION. 

over  the  edge,  so  that  the  inner  end  is  in  contact  with  the 
fluid,  and  the  outer  end  lower  than  the  inner,  the  fluid  will 
gradually  be  abstracted  by  a  syphon  action,  and  the  solid 
matter  left  nearly  dry.  A  little  temporary  syphon  of  this 
kind  is  often  very  useful  in  refrigerating  and  other  opera- 
tions :  being  connected  with  a  vessel  of  water,  it  will  supply 
a  small  quantity  of  that  fluid  constantly  during  a  long  pe- 
riod of  time. 

The  precautions  given  to  ensure  an  easy  separation  of  a 
precipitate  (517 — 521)  must  be  attended  to  in  washing  par- 
ticular bodies.  Prussian  blue  should  always  be  washed 
with  dilute  muriatic  acid  (519),  and  sulphate  of  baryta  with 
weak  nitric  acid,  and,  if  possible,  with  warm  water  (518). 

556.  It  will  be  observed  that  the  process  of  lixiviation  al- 
ready described  (420)  is  in  reality  a  washing  process.     What 
has  been  said  relative  to  it  will  be  abundantly  sufficient  to 
direct  its  application  to  substances  generally  when  neces- 
sary. 

557.  There  are  numerous  cases  in  chemistry  where  im- 
miscible fluids  are  to  be  separated  from  each  other.     Many 
of  these  are  not  difficult,  especially  where  the  substances  are 
unimportant  or  valueless;  but  sometimes  great  care  is  re- 
quired, because  of  the  value  of  the  bodies,  or  their  danger- 
ous nature.     A  case  of  separation  by  filtration  has  already 
been  pointed  out  *fo43).     In  other  circumstances  the  two 
fluids  may  be  poured  into  a  wet  funnel  (if  at  least  one  of  the 
two  be  water,  or  an  aqueous  solution),  closed  by  a  good  cork 
beneath,  and  left  to  remain  on  the  filtering  stand  until  separa- 
ted :  by  partly  withdrawing  the  cork,  the  lowermost  may  be 
almost  entirely  removed  from  the  upper.     Glass  vessels,  fur- 
nished with  a  stop-fcock  beneath,  are  made  for  this  purpose. 
Their  use  is  evident,  and  requires  no  description.* 

•Funnels  are  sometimes  furnished  with  conical  stoppers  which  may 
be  made  of  glass,  ground  to  fit  the  necks  ;  or  of  cork  supplied  with 
firmly  attached  handles — ED. 


a 


SEPARATION SEPARATORS.  263 

558.  Another  serviceable  instrument  is  a  glass  tube  with 
a  bulb  an  inch  in  diameter  blown  in  it,  and  drawn  out 
below  to  a  moderately  fine  aperture  (1197,  1179).     The 
aperture  being  immersed  in  either  the  upper  or   under 
liquid,  the  mouth  is  to  be  applied  above,  with  the  pre- 

\cautions  before   mentioned  (514),  and   the   air   with- 
/  drawn,  when  the  liquid  consequently  will  enter.     The 
finger  being  then  placed  on  the  upper  end  of  the  tube, 
so  as  to  close  it,  the  instrument  may  be  removed,  and 
the  fluid  within  transferred  to  any  convenient  vessel.* 

559.  A  useful  vessel  for  the  separation  of  a  small  quanti- 
ty of  valuable  fluid  may  be  made  of  a  piece  of  glass  tube 
from  the  third  to  a  quarter  of  an  inch  in  diameter,  by  draw- 
ing it  out  in  one  part  until  it  becomes  capillary 
(1176),  and  turning  it  up  as  in  the  figure.     The 
point  a  must  be  closed  in  the  flame  of  the  spirit 
lamp,  the  mixed  fluids  poured  into  the  tube,  and 
suffered  to  remain  till  separated.     The  point  a 
is  to  be  broken  so  as  to  open  an  aperture,  and 
then  by  inclining  the  instrument,  first  one  fluid, 

and  afterwards  the  other,  may  be  decanted.  The  fluids  will 
issue  drop  by  drop  into  the  vessels  placed  to  receive  them, 
and  the  surface  of  contact  of  the  two  in  the  fine  tube  is  so 
small,  that  scarcely  an  appreciable  portion  of  the  valuable 
one  need  be  wasted.  The  pouring,  or  transference  rather, 
is  more  steady  and  regular  when  the  beak  a  is  placed  against 
the  side  of  the  receiving  vessel,  so  that  no  drop  is  formed, 
but  a  continuous  minute  stream. 

560.  Finally,  glass  syringes,  such  as  have  already  been 
mentioned  (547),  are  very  advantageous  in  the  removal  and 
separation  of  fluids.     Such  an  one  as  that  figured  in  the 
woodcut  may  be  used  for  instance  in  the  management  of  the 

chloride  of  nitrogen. f  The  tow 
wrapped  round  the  wire  which  forms 
the  piston,  is  made  sufficiently  tight 
by  being  moistened  with  water,  and 

*  Dr  Hare  forms  a  more  convenient  instrument  by  attaching  to  the  upper  end 
of  this  tube  a  bag  of  gum-elastic.— ED. 
t  Brande,  Manual  of  Chemistry. 


264  CRYSTALLIZATION. 

when  not  inconvenient,  a  little  water  may  be  retained  both 
above  and  below  it.  The  beak  of  the  syringe  being  brought 
near  the  globules  of  the  chloride,  and  the  piston  moved  up- 
ward, the  substance  enters,  and  may  be  collected  by  holding 
the  instrument  in  the  position  in  which  it  is  figured.  It  may 
then  be  transferred  to  other  situations,  and,  if  required,  be 
made  to  issue  from  the  jet  perfectly  free  from  moisture. 
This  is  effected  by  holding  the  syringe  with  its  beak  down- 
ward against  a  piece  of  filtering  paper,  then  depressing  the 
piston,  till  the  water,  which  may  be  before  the  chloride,  is 
expelled,  and,  when  the  latter  is  on  the  point  of  issuing, 
by  removing  the  instrument  from  the  damp  paper  and  eject- 
ing the  pure  substance  into  the  desired  place,  by  a  further 
depression  of  the  piston.  Other  heavy  fluids  may  in  the 
same  way  be  separated  from  the  liquids  in  which  they  lie ; 
and  light  fluids  may  in  like  manner  be  drawn  up  and  re- 
moved, but  then  excess  of  water  must  not  be  left  below  the 
piston,  and  a  bubble  of  air  should  be  allowed  to  intervene 
between  it  and  the  substance  to  be  taken  into  the  instrument. 


SECTION  X. 
CRYSTALLIZATION. 

561.  CRYSTALLIZATION  is  a  very  useful  and  valuable  pro- 
cess in  the  laboratory.  It  enables  us  in  many  cases  to  pu- 
rify bodies  with  great  precision;  thus  by  crystallizing  the 
carbonate  of  soda,  a  pure  salt  is  obtained,  which  affords  a 
very  available  source  of  pure  soda ;  by  crystallizing  the 
acetate  and  the  nitrate,  similarly  pure  sources  of  the  alkali 
are  furnished.  Potash,  in  various  states  useful  for  combina- 
tions, atid  free  from  other  alkalies  or  earths,  is  obtained  by 
crystallizing  the  bi-carbonate  or  the  bi-tartrate  of  potash,  or 
nitre.  Pure  magnesia  is  obtained  from  a  crystallized  sul- 
phate;  pure  baryta  from  a  crystallized  nitrate;  pure  oxide 
of  nickel  from  its  sulphate;  and  pure  nitric  and  muriatic 
acids  are  obtained  from  nitre  and  common  salt,  previously 


CRYSTALLIZATION ITS  APPLICATION.  265 

rendered  free  from  other  bodies  by  this  process.  A  second 
object,  attained  by  crystallization,  is  the  very  definite  and 
convenient  state  conferred  upon  substances  by  it.  A  third, 
the  peculiar  but  precise  forms  and  appearances  which  it 
generally  imparts  to  them  :  these  serve  as  characters,  by 
which  known  bodies  may  be  recognized,  or  by  which  sub- 
stances before  confounded  together  may  be  distinguished 
from  each  other. 

562.  Crystallization  is  always  effected  in  the  laboratory 
by  bringing  the  particles  of  solid  Bodies  into  a  mobile  state, 
either  by  solution,  fusion,  or  vaporization.     It  is  not  to  be 
understood  that  these  are  the  only  methods  by  which  crystal- 
line form  or  structure  can  be  conferred,  for  there  are  suffi- 
cient proofs  to  show  that  a  body  not  crystalline  may  become 
so  without  changing  its  state  of  solidity.     The  crystallization 
of  cooling  basalt,  as  in  Mr  Watts'  experiments*,  or  of  heated 
glass,  or  of  barley  sugar,  or  even  the  spontaneous  change  of 
brass  wire,  which  in  a  few  years  becomes  brittle,  are  all  effects 
of  the  latter  kindf . 

563.  Considering  first  the  most  common  case,  that  of  crys- 
tallization from  an  aqueous  solution,    it  is  generally  per- 
formed in  one  of  two  ways, — by  cooling  a  hot  solution,  or  by 
slowly  evaporating  a  cold  one.     For  the  due  application  of 
the  first  and  most  useful  method,  it  is  necessary  that  the  sub- 
stance should  be  more  soluble  in  hot  water  than  in  cold  ;  and 
the  first  object  is  to  obtain  a  hot  solution  of  sufficient  strength 
to  deposit  crystals  when  of  a  common  temperature.     This 
may  be  procured  as  already  directed  (378),  or  a  weak  solu- 
tion may  be  evaporated  (590,  &c.),  till  of  sufficient  strength. 
A  very  convenient  mode  of  ascertaining  when  the  solution  is 
strong  enough  to  crystallize  is,  to  transfer  a  drop  of  it  by  a 
rod  (70),  to  a  cold  glass  plate,  and  observing  whether  it  de- 
posits crystals  as  the  temperature  falls  (379). 

564.  When  a  proper  solution  is  made,  and  filtered  if  ne- 
cessary, it  is  to  be  allowed  to  cool  undisturbed,  and  the  more 
gradually  this  is  done,  the  larger  will  be  the  deposited  crys- 

*  Philosophical  Transactions,  1804,  p.  282. 
f  Silver  crucibles  become  gradually  brittle  (659).— ED. 
2  I 


266  CRYSTALLIZATION FUOM  WATER. 

tals.  The  vessels  may  be  either  basins  (369),  pans,  or  such 
other  as  may  be  convenient,  having  regard  to  the  quantity 
and  quality  of  the  fluid.  They  should  resist  chemical  action, 
and  generally  be  of  glass  or  earthenware.  They  should  not 
be  shallow,  unless  a  rapid  crop  of  crystals  be  required,  and 
then  they  are  to  be  left  open.  A  depth  of  fluid  about  one 
half  or  one  third  of  its  horizontal  width  is  the  most  conve- 
nient for  the  quantities  usual  in  the  laboratory.  The  vessel 
should  be  covered  over,  to  prevent  evaporation  at  the  surface, 
where  otherwise  a  crust  of  crystals  would  frequently  form, 
disturbing  the  regularity  of  the  rest.  When  it  is  required  to 
cool  the  whole  slowly,  it  should  be  covered  with  a  flannel, 
or  cloth,  or  a  cone  of  paper  (1343).  Generally  speaking, 
when  the  solution  is  strong  in  the  first  instance,  agitated  dur- 
ing cooling,  and  the  temperature  diminished  rapidly,  the 
crystallization  is  quick,  confused,  and  irregular,  and  the  crys- 
tals small  :  but  when  the  solution  is  of  moderate  strength, 
the  cooling  allowed  to  go  on  slowly,  and  the  whole  retained 
in  a  quiescent  state,  the  crystallization  is  regular,  and  the 
crystals  are  large  and  distinct.  The  particular  proportions 
and  habitudes  of  each  substance  can  only  be  gained  by  ex- 
perience. 

565.  Crystallizations  to  be  effected  by  spontaneous,  or  very 
slow  evaporation,  require  a  solution  saturated  at  common 
temperatures.  This  may  be  obtained  as  before  mentioned 
(378),  and  must  have  more  surface  exposed  during  the  pro- 
cess than  was  required  in  the  former  method.  Evaporating 
basins  (369)  answer  this  purpose  very  well.  The  solution 
should  be  put  into  a  dry  place,  where  there  is  a  sufficient 
access  of  air  to  carry  off  the  vapour  which  will  gradually  rise 
from  it,  and  must  then  be  left  for  a  much  longer  period  than 
in  the  former  case.  It  is  advantageous,  if  the  place  be  so 
clean  that  no  dust  can  fall  into  the  solution  to  disturb  or 
contaminate  it,  to  leave  the  vessel  uncovered;  but  if  danger 
be  apprehended  on  that  point,  it  must  be  covered  either 
with  a  thin  dry  cloth,  stretched,  so  as  not  to  incur  any  risk 
of  its  sinking  into  the  solution,  or  else  by  filtering  paper. 
When,  however,  an  evaporating  solution  is  thus  covered,  the 


CRYSTALLIZATION PAPER  COVERS.  267 

process  is  considerably  interfered  with,  and  much  more  time 
required. 

566.  These  vessels,  as  well  as  glasses,  and  many  others 
having  round  apertures,  are  occasionally  very  conveniently 
covered  with  paper ;  for  which  purpose  a  piece  of  paper,  so 
large  as  to  overlap  the  vessel  from  half  an  inch  to  an  inch  on 
every  side,  being  placed  over  the  aperture,  should  be  folded 
down  on  one  side  against  the  vessel.     Then  a  second  fold, 
an  inch  from  the  first  and  partly  overlapping  it,  is  to  be 
made ;  a  third  upon  that,  and  so  on,  until  the  folds  have 
reached  round  the  aperture.     These  hold  each  other  down, 
and  the  last  may  be  fastened  by  screwing  it  up  tightly,  the 
whole  being  done  somewhat  in  tire  manner  that  a  grocer 
finishes  his  paper  case  for  a  small  quantity  of  sugar.     The 
temporary  cover  thus  formed  fits  the  mouth  of  the  vessel 
tightly,  is  strained  level  over  its  surface,  incurs  no  risk  of 
sinking  into  the  solution  beneath,  and  being  held  on  by  the 
ledge  formed  from  the  succession  of  folds,  is  not  easily  dis- 
placed or  disturbed. 

567.  It  is  by  the  process  of  slow  evaporation  that  the  larg- 
est crystals  are  obtained.     A  few  of  perfect  forms  should  in 
the  first  place  be  selected,  and  these,  being  placed  in  the 
solution,  increase  in  size  as  the  evaporation  proceeds,  and 
ultimately  become  very  large.     They  must  be  turned  every 
day,  that  all  sides  may  receive  increments  of  solid  matter  in 
succession. 

568.  An  advantageous  process  between  the  two  now  de- 
scribed may  often  be  resorted  to ;  it  consists  in  placing  a 
moderate  or  weak  solution  on  the  sand-bath  in  the  evening 
when  the  fire  is  going  out,  heaping  the  sand  round  the  basin, 
and  leaving  the  whole  until  the  morning.     The  evaporation 
is  somewhat  hastened,  and  at  the  same  time  the  temperature 
falls  very  slowly  ;  and  thus  in  many  cases  a  fine  crop  of  crys- 
tals may  be  obtained  in  a  short  period. 

569.  For  most  substances  the  first  method  (563)  is  pre- 
ferable:  thus  acetate  of  lead,  sulphate  of  soda,  nitre,  &c., 
are  better  so  crystallized  ;  but  for  a  few  others,  the  second 
(565)  is  most  advantageous,  and  such  are  common  salt,  bo- 
rax, Rochelle  salt,  sulphate  of  potash,  &c. 


268          LARGE  CRYSTALS  FROM  SMALL  ONES. 

570.  A  very  interesting,  and,  in  some  cases,  useful  process, 
is  the  gradual  conversion  of  several  small  crystals  into  one 
large  one.     Dr  Wollaston,  who  communicated  it  to  me,  per- 
mitted me  also  to  describe  it.     If  a  small  quantity  of  sul- 
phate of  nickel  in  solution,  with  a  slight  excess  of  acid,  be 
evaporated  in  a  watch-glass,  it  will  probably,  on  cooling, 
yield  a  crop  of  numerous  small  crystals  ;  but  if  set  aside  for 
a  few  weeks  in  a  place  subject  to  the  changes  of  atmospheric 
temperature,  its  appearance  will  gradually  alter,  the  small 
crystals  disappearing,  the  larger  increasing,  until  ultimately 
only  one  or  a  few  large  ones  are  left.     This  effect  depends 
on  the  greater  extent  of  surface  exposed  by  the  small  crys- 
tals, as  compared  to  their  mass,  than  by  the  larger  crystals; 
so  that  when  any  increase  of  solvent  power  in  the  surround- 
ing fluid  is  occasioned  by  a  slight  increase  of  heat  in  the  at- 
mosphere, the  small  crystals  dissolve  to  a  greater  extent  than 
the  others ;  but,  upon  the  decrease  of  temperature,  the  de- 
position is  equal  upon  all.     In  this  manner  the  small  ones 
are  gradually  dissolved,  and  the  large  ones  become  larger. 
Thus  sometimes  a  separation  from  impurities,  a  perfection  of 
form,  or  a  crystal  of  magnitude  is  obtained,  which  cannot 
be  had  by  other  means.     The  same  effect  may  often  be  ob- 
served in  solutions  confined  in  glass  bottles,  as  in  oxalic  acid, 
nitrate  of  mercury,  acetate  of  lead,  &c.;  the  small  crystals 
which  were  formed  when  the  solutions  were  first  made  being 
gradually  converted  into  others  of  considerable  magnitude. 

571 .  Other  solvents  than  water  must  be  used  for  substances 
not  soluble  in  that  fluid,  and,  at  times,  even  for  some  that 
are.     Alcohol  is  applicable  to  the  crystallization  of  potash, 
cholesterine,  urea,  sugar,  &c.     Alcoholic  solutions  are  ge- 
nerally crystallized  by  spontaneous  evaporation,  unless  in- 
deed the  solution  has  been  introduced  into  a  retort,  for  the 
purpose  of  distilling  part  of  the  spirit,  and  then  the  remain- 
ing fluid  is  generally  best  left  in  the  retort,  to  cool  and  crys- 
tallize.    Ether,  oil  of  turpentine,  and  pyroligneous  ether,  are 
now  and  then  employed  in  experiments  on  unknown  substan- 
ces, for  the  purpose  of  discovering  characters  by  which  they 
may  be  distinguished. 

572.  The  influence  exerted  over  one  substance  by  the 


CAUSES  INFLUENCING  FORMS.  269 

presence  of  another,  which  often  materially  affects  the  ap- 
pearances of  crystals  and  crystallizations,  must  now  be  no- 
ticed. Nitre,  when  crystallizing  from  solutions  containing 
much  common  salt,  is  frequently  rough  upon  its  surface,  or 
constituted  of  a  number  of  crystals,  forming  a  friable,  instead 
of  a  compact,  mass.  Common  salt,  when  crystallized  from  a 
solution  containing  urea,  or  in  urine,  assumes  an  octohedral 
form.  It  has  also  the  same  form,  though  imperfectly,  when 
crystallizing  at  the  surface  of  a  solution  during  evaporation. 
The  appearances  of  several  salts  are  altered  when  crystal- 
lized in  animal  or  vegetable  infusions.  The  most  remarka- 
ble instance  of  the  kind,  and  one  which  deserves  notice  here 
in  consequence  of  the  great  apparent  difference  produced, 
although  not  likely  often  to  happen  accidentally,  is  when 
strong  sulphuric  acid  has  acted  upon  some  of  the  products  of 
distilled  or  decomposed  oil.  If  one  part  of  the  substance 
obtained  by  the  compression  of  oil  gas,  and  which  always 
exists  as  vapour  in  it,  be  mixed  with  eight  or  ten  parts  of 
strong  oil  of  vitriol,  a  dark  liquor  is  produced  ;  from  this, 
when  diluted  with  water,  filtered,  and  converted,  by  the  ad- 
dition of  carbonate  of  potash,  into  a  sulphate  of  potash,  a 
salt  is  obtained,  which,  upon  crystallization,  is  nacreous,  in 
the  form  of  scales,  and  has  nothing  in  its  appearance  com- 
mon to  sulphate  of  potash.  It  is,  however,  that  salt,  and  is 
thus  affected  by  a  substance  which  sometimes  does  not 
amount  to  a  two-hundredth  part  of  the  salt  present.  The 
same  substance  has  still  greater  power  over  the  sulphate  of 
copper,  and  in  increased  quantities  (still  comparatively  very 
small)  influences  the  appearances  of  a  great  many  saline 
bodies. 

573.  Sometimes  crystallization  is  not  effectual  for  the  se- 
paration of  salts.  When  the  sulphates  of  iron  and  copper 
are  in  solution  together,  crystals  will  be  obtained  resembling 
those  of  sulphate  of  iron,  but  with  very  variable  proportions 
of  sulphate  of  copper  in  them,  the  latter  salt  being  present 
at  times,  in  great  quantity ;  on  other  occasions  triple  salts 
are  formed,  as  frequently  occurs  with  nickel.  But  these,  and 
a  knowledge  of  many  more  extraordinary  circumstances  at- 


270  CRYSTALLIZATION INDICATED EXAMINED. 

tending  crystallization,  must  be  left  to  be  obtained  by  read- 
ing and  experience. 

574.  When  salts  which  may  be  separated  from  others  by 
crystallization  have   been  obtained  from  impure  solutions, 
they  always  retain  a  portion  of  the  impurities,  and  require  to 
be  redissolved.and  recrystallized,  before  they  can  be  consi- 
dered as  approaching  to  purity.     In  particular  cases  even  a 
third  crystallization  is  necessary. 

575.  When  experiments  are  proceeding  upon  an  unknown 
substance  or  a  mixture  of  substances,  to  ascertain  whether  it 
will  crystallize  or  not,  they  are  generally  made  as  distinctly 
and  effectually  upon  a  small  scale  as  a  large  one,  and  often 
indeed  with  more  success  (916).     Thin  fragments  of  Florence 
flasks  are  useful ;  as  are  little  dishes,  capsules,  watch-glas- 
ses, and  the  glass  plates,  already  briefly  mentioned  (1348). 
Sometimes  merely  by  dipping  a  rod  into  the  hot  solution, 
and  allowing  the  surface  thus  wetted  to  dry  in  the  air,  it  may 
be  observed  from  the  striated,  regular,  or  uniform  appear- 
ance, whether  the  substance  has  crystallized  upon  it.     At 
other  times,  a  drop  of  the  cold  solution  may  be  put  upon  a 
flat  glass  plate,  and  the  latter  placed  on  a  warm  part  of  the 
table  furnace,  that  the  liquor  may  slowly  evaporate,  and  from 
the  examination  of  the  spot  of  solid  matter  left,  a  judgment 
may  be  formed.     But  perhaps  the  most  decisive  evidence  is 
to  be  gained  by  leaving  a  drop  or  a  small  portion  in  a  piece 
of  Florence  flask  to  evaporate  spontaneously  at  common 
temperatures ;  or,  if  the  substances  dissolved  are  deliques- 
cent, by  evaporating  them  under  the  air-pump  receiver  (583). 
The  crusts  of  solid  matter  thus  produced  should  be  examin- 
ed with  care ;  as  well  with  a  powerful  eye-glass  as  by  the 
naked  eye;  sometimes  by  holding  the  glass  plate  in  the  sun's 
ray  whilst  it  is  regarded  sideways,  or  by  the  light  from  a 
•candle  reflected  by  it  to  the  eye,  or  by  looking  through  the 
crust  and  glass,  not  directly  at  the  light,  but  at  a  back  ground 
close  to  it.     In  all  these  trials  appearances  which  resemble 
crystallization  should  be  closely  scrutinized,  for  the  manner 
in  which  a  film  cracks  or  scales,  or  the  way  in  which  the 
surface  of  a  fluid  in  small  quantities  is  drawn  by  contraction, 


CRYSTALLIZATION BY  DISSECTION FUSION.  271 

is  often  such  as  to  occasion  appearances  so  deceitful  as  to 
make  it  absolutely  necessary  to  refer  to  an  eye-glass. 

576.  Mr  Daniell  has  introduced  a  process  of  dissection*, 
which,  though  not  concerned  in  the  production  of  crystals, 
is  frequently  of  great  advantage  in  developing  them  from 
amorphous  masses,  and  showing  the  relation  of  forms  one  to 
another.  It  consists  in  putting  a  mass  of  the  substance  into 
a  fluid  capable  of  dissolving  it,  which  gradually  removing 
the  exterior  parts,  reveals  the  interior  in  their  symmetric  ar- 
rangement. When  the  substance  is  moderately  soluble,  like 
alum,  a  lump  of  it  should  be  put  into  water,  equal  to  about 
its  own  bulk  in  quantity,  and  in  such  a  vessel  that  the  fluid 
may  rise  a  little  above  its  surface,  and  should  be  left  for  se- 
veral days  in  a  quiet  place  of  uniform  temperature.  It  will 
then  be  found,  upon  examination,  that  crystalline  forms  have 
been  developed  by  the  solvent  action  of  the  water. 

577.  Bodies  but  slightly  soluble,  as  sulphate  of  potash, 
may  have  more  water  put  over  them.     On  the  contrary, 
such  as  are  very  soluble,  in  place  of  being  immersed  in  wa- 
ter, should  be  put  into  a  solution  of  the  same  substance, 
which  having  been  saturated,  has  afterwards  been  slightly 
diluted  to  occasion  a  solvent  action.     Substances  not  solu- 
ble in  water,  but  soluble  in  acids,  without  effervescence,  may 
be  successfully  examined  in  the  same  manner. 

578.  As  before  mentioned,  the  crystallization  of  some  sub- 
stances may  be  effected  by  fusion,  when  solution  is  scarcely 
applicable,  and  thus,  many  metals,  sulphur,  spermaceti,  &c., 
may  be  made  to  assume  crystalline  forms.     The  process  on- 
ly succeeds  well  with  large  quantities,  and  may  be  illustrat- 
ed by  reference  to  lead  or  bismuth.     The  metal  is  to  be 
put  into  an  iron  ladle  and  melted,  the  ladle  removed  from 
the  fire  and  placed  on  the  sand-bath,  where,  though  the  bot- 
tom may  be  kept  warm,  the  heat  is  not  such  as  to  prevent 
the  top  from  congealing.     When  a  solid  crust  has  formed, 
holes  should  be  broken  through  it  at  two  opposite  parts 
near  the  edge,  with  a  hot  iron  rod,  and  the  fluid  metal  rapid- 
ly poured  out.     When  that  which  remains  in  the   ladle  is 

*  Quarterly  Journal  of  Science,  i.  24. 


272  CRYSTALS BY  VAPORIZATION EXAMINED. 

examined,  it  will  be  found  crystallized  in  the  interior.  A 
crucible  may  be  used  in  place  of  an  iron  ladle  for  metals ;  a 
glass  flask  or  an  evaporating  basin  for  sulphur,  spermaceti, 
or  similar  substances.  When  the  experiment  is  made  with 
sulphur,  the  temperature  should  not  be  raised  too  high,  or 
the  fluid  will  thicken  and  become  adhesive. 

579.  When  crystals  are  to  be  obtained  by  vaporization, 
the  general  directions  given  with  regard  to  sublimation  (495, 
&c.)  are  to  be  followed;  it  is  to  be  observed,  however,  that 
the  more  slowly  and  regularly  the  crystals  are  formed,  the 
finer  are  the  forms  obtained.     It  is  easy  to  sublime  and 
crystallize  such  bodies  as  camphor,  iodine,  naphthaline,  &c., 
but  with  those  which  demand  a  higher  temperature,  as  calo- 
mel or  corrosive  sublimate,  good  crystals  can  be  obtained 
only  by  operating  with  large  quantities.     The  crystallization 
of  indigo  is  best  effected  as  already  described  (499). 

580.  In  examining  crystals,  with  a  view  to  recognize  their 
general  form  and  appearance,  or  the  existence  of  any  par- 
ticular plane,  it  may  be  observed  that  the  eye  should  be  as- 
sisted by  an  eye-glass,  and  sometimes  by  placing  the  crys- 
tals in.  the  sun's  light,  or  in  the  light  of  a  lamp,  or  candle, 
that  the  reflection  from  the  planes,  as  they  come  into  par- 
ticular positions,  may  render  them  evident ;  and  it  may  also 
be  observed,  that  where  small  crystals  or  fragments  of  sub- 
stances are  to  be  taken  up  and  examined  by  the  eye,  a  soft 
cement,  composed  of  two  parts  yellow  wax  and  one  part 
turpentine,  is  very   useful  (1125).     A  little  piece  of  this, 
softened  between  the  fingers,  may  be  fixed  on  the  end  of  a 
pencil  or  a  small  stick,  and  formed  to  a  point,  or  a  small  roll 
of  the  substance  itself  may  be  pointed  at  the  end,  and  the* 
particle  being  touched  by  this  point  immediately  adheres  to 
it,  and  may  be  examined  with  perfect  ease. 

581.  With  reference  to  the  use  of  the  goniometer,  espe- 
cially the  accurate  instrument  of  Dr  Wollaston's  invention, 
and  also  to  the  determination  of  the  forms  of  crystals  them- 
selves, these  constitute  a  part  of  that  extensive,  important? 
and  mathematical  branch  of  knowledge  now  known  by  the 
name  of  Crystallography ;  and  for  such  information  as  re- 
lates to  the  use  of  the  instruments  required  in  it,  the  student 


EVAPORATION ITS  NATURE.  273 

is  referred  to  the  paper  by  Dr  Wollaston  in  the  Philosophi- 
cal Transactions  for  1809;  Phillips'  Elementary  Introduc- 
tion to  Mineralogy;  and  Brooke's  Introduction  to  Crystallo- 
graphy. 


SECTION  XL 
EVAPORATION— DESICCATION. 

582.  EVAPORATION  is  a  process  so  simple  in  its  nature, 
and  common  in  its  performance,  as  to  be  comprehended  ge- 
nerally by  every  one.     The  ordinary  vessels  required  for  it 
are  basins  of  earthenware  (369),  one  or  two  of  silver  and 
lead  (371),  a  crucible  and  capsules  of  platinum  (371),  Flo- 
rence flasks  (373),  fragments  of  flasks  (1213),  and  watch- 
glasses.     The  basins  and  capsules  of  earthenware  should  be 
thin  at  the  bottom,  Jbut  all  these  vessels  have  been  suffi- 
ciently described  ftf  the  section  upon  Solution. 

583.  Of  evaporation,  at  common  temperatures,  that  which 
is  performed  spontaneously  has  been  referred  to  in  treating 
of  crystallization  (565),  and  the  necessity  of  a  clean  airy 
place,  or  of  covering  the  vessels,  insisted  upon.     But  the 
process  has  been  very  much  assisted  and  hastened  by  the  use 
of  desiccators,  and  in  the  hands  of  Mr  Leslie*  has  been  car- 
ried to  an  extent,  in  its  power  and  application,  surpassing 
every  previous  expectation.     Mr  Leslie's  process  consists  in 
placing  the  fluid  to  be  evaporated,  in  a  basin  so  as  to  expose 
considerable  surface,  under  the  receiver  of  an  air  pump,  ac- 
companied by  another  basin,  containing  a  substance  which 
has  strong  attractive  powers  for  water.     Sulphuric  acid,  hav- 
ing a  surface  of  from  twice  to  thrice  that  of  the  fluid  to  be 
evaporated,  may  be  used.     These  should  be  so  placed  that 
the  first  basin  may  be  supported  over  the  second  ;  and  both 
being  covered  by  a  receiver  as  small  as  can  be  conveniently 
used,  it  is  to  be  exhausted,  and  the  operation  left  to  itself. 

*  Supplement  to  Ency.  Britannica,    Art.  Cold. 

2  K 


274 

The  air  being  absent  from  within  the  receiver,  a  ready  libe- 
ration of  vapour  from  the  water,  equivalent  in  tension  to  its 
temperature,  takes  place ;  but  this  vapour  is  as  rapidly  con- 
densed upon  coming  into  contact  with  the  sulphuric  acid, 
and  its  place  supplied  by  fresh  vapour  from  the  water, 
which  in  turn  is  condensed  as  before.  Thus  the  process 
goes  on,  the  water  travelling  in  the  form  of  vapour  from  the 
basin  to  the  sulphuric  acid,  where  it  combines  and  resumes 
the  liquid  state. 

584.  This  process  of  evaporation  and  consequently  of  de- 
siccation, is  valuable,  not  merely  as  avoiding  any  necessity 
for  elevation  of  temperature,  but  as  actually  causing  consi- 
derable depression,  and  is  for  this  reason  useful  in  numerous 
cases  where  delicate  organic  substances,  which  might  be 
injured,  even  by  moderate  heat,  require  drying.     For  its 
operation,  all  that  is  necessary  is,  to  replace  the  basin  of  wa- 
ter by  the  substance  to  be  dried ;  whether  it  be  fibre,  or  a 
filter  with  a  precipitate  upon  it,  or  a  portion  of  washed  pre- 
cipitate in  a  basin,  or  a  solution.     All  these  or  any  other 
substances,  in  basins,  may  be  supported  by  a  little  tripod 
with  glass  legs,  standing  in  the  dish  of  sulphuric  acid. 

585.  In  the  general  arrangement  of  this  process,  it  is  ne- 
cessary that  the  pump  be  in  such  order,  and  the  receiver 
fitted  so  accurately  to  the  plate,  that  the  vacuum  may  be 
retained  for  days  together.     It  is  also  necessary  that  the  sul- 
phuric acid  be  not  allowed  to  become  too  dilute  by  frequent 
use.     It  is  most  powerful  when  first  introduced,  should  be 
stirred  up  now  and  then  when  the  receiver  is  opened,  and 
had  better  be  replaced  by  fresh  acid  when  diluted  with  a 
fourth  or  fifth  its  weight  of  water.     Care  should  be  taken 
to  prevent  all  contact  between  the  acid  and  the  bodies  to  be 
dried  ;  and  the  student  should  be  aware,  that  upon  the  first 
exhaustion  after  the  introduction  of  fresh  acid,  there  is  ge- 
nerally the  evolution  of  a  little  air,  which,  forming  bubbles 
at  its  surface,   break   and  throw  up  minute  drops.     Care 
should  be  taken  that  these  drops  cannot  reach  the  substance 
to  be  dried. 

586.  Although  the  arrangement  described  is  the  most 
powerful,  it  may  not  always  be  the  most  convenient.     The 
substance  to  be  dried  may  be  in  a  glass  or  bottle  ;  which  may 


EVAPORATION — COOPER'S  METHOD.  275 

stand  in  the  dish  containing  the  acid,  or  the  acid  itself  may 
be  in  a  glass  by  the  side  of  the  substance ;  but  in  all  cases 
the  acid  should  be  in  a  very  open  vessel,  for  if  in  a  close  one, 
its  small  surface  soon  becomes  diluted  and  rendered  ineffec- 
tual ;  and  moreover,  as  there  is  also  a  tendency  in  the  process 
to  accumulate  the  portion  of  air  left  in  the  receiver  in  the 
vessel  containing  the  acid,  it  retards  the  condensation,  and 
consequently  the  operation.* 

587.  Mr  Cooper  has  a  method  of  setting  several  of  these 
operations,  on  a  small  scale,  at  work  at  one  time.     It  consists 
in  the  use  of  glass  plates,  in  addition  to  the  receiver  and  its 
contents.     These  plates,  like  those  referred  to  (575,  1348), 
are  of  thick  plate  glass,  but  each  has  a  small  hole  drilled 
through  it  at  about  one  fourth  the  diameter  from  the  edge. 

These  plates,  with  a  little  pomatum  or  oil  between 
them,  are  perfectly  air  tight,  and  two  thus  prepared, 
being  placed  together,  with  the  holes  coincident, 
allow  a  free  passage  for  the  air  through  them,  but 
by  being  turned  a  little  way  round  one  upon  the 
other,  the  holes  are  separated,  and  the  passage  closed.  Mr 
Cooper  places  a  jar  with  an  open  ground  top  upon  the  plate 
of  the  air  pump,  on  it  two  of  the  glass  plates  with  the  holes 
coincident,  and  the  basin  of  sulphuric  acid  with  its  glass  and 
receiver  upon  the  upper  plate.  The  pump  is  then  worked, 
both  receivers  are  exhausted,  and  when  in  that  state  the 
plates  are  moved  one  upon  the  other,  so  as  to  close  the  com- 
munication, air  is  let  into  the  lower  receiver,  and  the  upper 
receiver,  with  its  contents  standing  upon  the  two  plates,  is 
set  aside  for  a  few  days  or  a  longer  time,  as  may  be  required. 
Instead  of  using  the  lower  receiver,  the  plates  may  be  put 
directly  upon  the  air  pump,  the  aperture  in  it  coinciding  with 
those  in  the  plates. 

588.  More  imperfect,  but  yet  very  useful  processes,  may 

*  It  is  not  easy  to  understand  the  last  part  of  this  sentence. — The  air  cannot 
accumulate  in  any  particular  part  of  the  receiver  or  vessel,  but  must  be  equally 
distributed  throughout.  But  the  air  In  the  vessel  containing  the  acid  may  be 
made  drier  than  the  rest,  because  the  narrow  mouth  permits  the  diffusion  of  the 
moisture  at  a  rate  less  than  the  absorbent  power  of  the  larger  surface  within;  and 
moreover  the  escape  even  of  a  small  quantity  of  dry  air  from  the  acid  itself,  by 
creating  a  slight  current  outwards,  may  obstruct  the  entrance  of  the  moisture  from 
the  receiver. — ED. 


276  EVAPORATION — BY  DESICCATORS. 

be  practised  without  the  aid  of  an  air  pump.  If  the  acid 
and  the  substance  to  be  dried  be  placed  in  a  proper  position 
upon  a  glass  plate  of  sufficient  size,  rubbed  with  pomatum, 
and  a  receiver  covering  them,  accurately  closed  upon  the 
plate,  then,  by  raising  the  receiver,  introducing  the  flame  of 
a  spirit  lamp  for  a  moment,  and  suddenly  replacing  it  accu- 
rately upon  the  glass,  as  is  practised  by  cuppers,  an  exhaus- 
tion will  be  obtained,  imperfect  it  is  true,  but  which  still  will 
usefully  facilitate  the  evaporation. 

589.  Even  without  any  process  of  exhaustion,  evaporation 
at  common  temperatures  may  be  carried  on  by  the  use  of 
desiccators,  more  rapidly  in  close  vessels  than  in  the  open 
air,  unless,  indeed,  a  current  be  taken  advantage  of;  and  a 
wide-mouthed  stoppered  bottle,  or  a  jar  placed  over  or  in  a 
basin,  will  at  times  supply  the  want  of  better  apparatus.     In 
these  cases  sulphuric  acid,  chloride  of  calcium,  carbonate  of 
potash,  quick  lime,  and  similar  absorbents,  may  be  used.     A 
basin  of  quick  lime,  with  a  moist  precipitate  placed  above  it, 
and  the  whole  covered  with  a  jar  or  receiver,  will  soon  dry 
the  precipitate. 

590.  When  there  is  no  objection  to  the  application  of 
heat,  evaporation  may  be  rapidly  effected  by  its  assistance. 
The  heat  being  supplied  in  one  or  other  of  the  numerous  me- 
thods already  referred  to  in  distillation  (section  vii.)  and  so- 
lution (section  vi). 

591.  If  the  evaporation  is  to  be  performed  at  temperatures 
under  ebullition,  the  vessel  used  should  be  an  open  one,  as 
a,  basin  (369),  and  have  free  access  of  air,  that  the  aqueous 
vapour  may  be  removed  from  the  surface  of  the  liquid  by 
the  aid  of  the  atmosphere,  as  fast  as  it  is  produced  (943). 
When  crusts  form  on  the  surface,  they  should  be  broken 
down,  for  they  interfere  much  with  the  evolution  of  vapour, 
acting  indeed  the  same  part  as  a  cover,  or  the  film  of  oil  be- 
fore mentioned  (260);  the  effect  which  before  was  advanta- 
geous being  now  injurious. 

592.  If  the  evaporation  be  required  todryness,  as  is  com- 
mon in  cases  of  analysis,  great  care  is  necessary  when   the 
solid  matter  begins  to  be  in  such  proportion  to  the  liquid  as 
to  form  a  thick  mixture.     The  circulation  which  took  place 


EVAPORATION STIRRING VESSELS.  277 

throughout  is  now  interrupted,  and  the  heat  will  frequently 
increase  at  the  bottom  of  the  basin  until  above  the  boiling 
point  of  the  solution,  before  it  can  pass  by  conduction  through 
the  crust  above  it.  Then  occurs  the  sudden  evolution  of 
small  portions  of  steam,  which  cause  sputtering  and  petty 
explosions,  and  throw  the  substance  about.  In  such  cases 
it  is  necessary  to  stir  the  substance  continually,  that  by  mix- 
ing the  whole  together,  the  one  part  may  be  prevented  from 
rising  to  too  high  a  temperature,  and  the  other  be  more  readily 
evaporated  to  dryness.  It  assists  also  in  making  way  for  the 
steam  from  the  lower  part,  and  materially  facilitates  the  de- 
siccation. It  is  even  necessary,  when  part  of  the  matter  has 
become  so  dry  as  to  harden  into  lumps,  to  use  a  pestle  in 
place  of  a  glass  rod,  and  by  rubbing  the  lumps  down  and 
mixing  them  with  the  moist  parts,  to  bring  the  whole  gradu- 
ally into  the  state  of  an  uniform  dry  powder.  When  this  is 
done  for  analysis,  great  care  must  be  taken  not  to  lose  any 
portion  of  that  which  adheres  to  the  rod  or  the  pestle  :  it 
must  be  scraped  off  with  the  platinum  spatula,  and  the  rod 
and  pestle  being  washed  with  a  little  water,  the  liquid  must 
be  reserved  to  be  added  to  the  rest  in  due  time. 

593.  Sometimes  when  substances  which  dry  hard,  as  a 
solution  of  common  salt,  are  left  to  evaporate  without  stir- 
ring, they  form  a  cake,  between  which  and  the  bottom  of 
the  basin  portions  of  steam  are  generated,  with  a  force  not 
merely  sufficient  to  throw  out  a  part  of  the  contents,  but  ac- 
tually to  cause  violent  explosions,  breaking  the  basin  to  pie- 
ces, and  dispersing  the  substance  in  all  directions.     This  is 
entirely  prevented  by  frequent  stirring.     When,  from  the 
habits  of  the  salt,  no  fear  is  entertained  of  such  an  occur- 
rence, stirring  may  be  dispensed  with  in  operations  not  re- 
quiring exactness,  the  evaporating  basin  being  then  covered 
by  another  to  prevent  the  loss  of  any  small  particles  thrown 
up.     The  upper  must  then  be  retained  in  a  heated  state, 
which  may  be  done  by  filling  it  with  sand,  otherwise  the  de- 
siccation will  not  proceed,  for  the  vapour  condensing  upon 
the  cold  cover  will  return  to  the  substance  below  in  drops. 

594.  If  the  fluid  is  to  be  evaporated  at  a  boiling  tempera- 
ture, there  is  no  necessity  for  its  being  done  in  an  open  vessel, 
though  it  is  always  most  rapidly  so  performed.     It  may  then 


278  EVAPORATION COVERS  FOR  THE  VESSELS. 

be  effected  either  in  basins  or  flasks.  In  the  latter  case  the 
dry  results  are  not  so  easily  removed,  but  that  is  often  of  no 
consequence,  and  occasionally  flasks  present  decided  advan- 
tages. The  analysis  of  a  mineral  water  often  requires  that 
large  quantities  of  fluid  be  evaporated  :  these  being  too  great 
for  introduction  at  one  time,  are  introduced  by  successive 
portions ;  and,  as  much  time  is  required,  the  evaporation 
should  be  performed  so  as  to  avoid  the  dispersion  of  any  part, 
and  prevent  the  entrance  of  fumes  or  other  extraneous  mat- 
ter. The  quart  Florence  flasks  are  then  very  useful ;  the 
boiling,  and  consequently  the  evaporation,  may  proceed  ra- 
pidly in  them  on  the  sand  bath,  fresh  portions  of  water  be- 
ing added  as  that  in  the  flask  diminishes,  until  all  is  reduced 
to  a  small  quantity,  which  may  then  be  decanted,  the  flask 
washed  out,  and  this  last  and  concentrated  portion  treated  as 
the  analysis  may  require. 

595.  The  entrance  of  dirt  at  the  small  aperture  of  the  flask 
may  be  prevented  by  rolling  up  a  piece  of  paper  into  a  co- 
nical form,  and  putting  it  loosely  into  the  mouth  as  a  stop- 
per, or  covering  it  in  the  manner  of  an  extinguisher.     Either 
method  will  allow  free  passage  for  the  vapour. 

596.  When  evaporations  are  going  on  at  the  boiling  tem- 
perature in  a  basin,  it  is  still  more  requisite  that  the  vessel 
be  covered,  inasmuch  as  the  ebullition  will  more  probably 
throw  small  portions  of  fluid  out,  and  dirt  and  vapours  are 
more  likely  to  find  their  way  in.     The  best  cover  is  a  second 
basin  put  over  the  first  and  retained  hot  (593) ;  or  if  the 
evaporating  dish  be  small,  one  of  the  bottom  covers  (553),  or 
a  watch-glass  may  be  used.     It  is  necessary  in  all  these  eva- 
porations, as  M.  Berzelius  has  observed,  that  the  cover  dip 
downwards,  so  that  any  fluid  condensed  on  it  may  return  to 
that  below,  and  not  run  to  the  outside  of  the  vessel :  for  the 
particles  of  matter  in  solution  being  thrown  up  and  caught 
by  the  cover,  are  thus  returned  to  the  place  from  whence 
they  came  ;  whereas  in  the  other  case,  they  would  be  carried 
to  the  outside  and  lost.     The  steam  makes  its  way  out  at  the 
lip  of  the  basin.     The  necessity  during  these  close  evapora- 
tions of  keeping  up  the  heat,  will  be  evident  from  the  obser- 
vations already  made  (425). 

597.  With  a  view  to  particular  substances  in  a  mineral 


EVAPORATION HEAT  FOR  ORGANIC  PRODUCTS.     279 

water,  which  it  is  feared  may  be  confounded  with  any  thing 
that  by  possibility  could  be  separated  from  the  glass  of  a 
Florence  flask  by  long  boiling,  it  is  sometimes  required  to 
carry  on  the  evaporation  in  a  metallic  vessel.  A  deep  silver 
crucible,  or  vessel,  is  probably  the  best  apparatus  that  will 
present  itself,  though  one  of  platinum  would  be  better.  The 
vessel  must  be  perfectly  clean,  and  covered  with  a  silver  or 
platinum  dish  in  the  manner  just  described  (596).  The  wa- 
ter must  be  added  in  successive  portions. 

598.  When  heat  is  applied  by  a  sand-bath  to  a  basin  dur- 
ing evaporation,  the  precautions  pointed  out  (381,  382)  are 
to  be  observed.     When  the  temporary  hood  (392)  is  in  use, 
care  must  be  taken  that  the  inside  be  clean,  that  nothing; 
may  fall  from  it  to  contaminate  the  substance  in  the  basirt 
beneath. 

599.  Solutions  of  animal  and  vegetable  substances  are 
frequently  to  be  evaporated  and  dried,  until  they  become 
free  from  water  or  retain  but  a  small  portion  of  it.     In  these 
cases,  if  the  heat  be  that  of  a  sand-bath  or  lamp,  the  tem- 
perature is  ultimately  apt  to  increase  to  such  a  degree  at 
the  bottom  of  the  basin,  as  to  cause  injury  to  the  substance. 
The  solution,  or  extract,  should  be  constantly  stirred  as  it 
thickens,  and  as  a  thermometer  cannot  be  applied  so  as  to 
indicate  the  heat  at  the  bottom,  another  method  must  be 
adopted  for  that  purpose.     Sir  Humphry  Davy  recommends 
that  a  chip  of  wood  be  retained  in  contact  with  the  exterior 
of  the  basin  at  the  bottom.     When  the  temperature  is  pow- 
erful enough  to  char  the  wood,  it  is  sufficient  to  cause  inju- 
ry to  the  contents  of  the  vessel,  and  upon  the  first  indication 
the  latter  should  be  removed.     A  few  slips  of  paper  laid  be- 
tween the  basin  and  the  sand,  when  a  sand-bath  is  used,  an- 
swer the  purpose  very  well,  and  indicate  by  their  changes 
the  power  of  the  temperature  to  which  the  basin  is  subject. 
As  some  substances  decompose  by  heat  before  others,  it  is 
advantageous  to  have  corresponding  indications;  and  if  slips 
of  worn  calico  be  used,  they  will  undergo  a  change  at  tem- 
peratures much  below  those  which  affect  paper.     In  cases, 
therefore,  where  more  care  is  required,  the  former  substance 
should  be  used  instead  of  the  latter. 

600.  Similar  care  is  required  in  the  desiccation  of  organic 


280          TEST  OF  DRY.NESS — CURRENTS — AIR-CHAMBER. 

substances  in  a  pulverulent  or  divided  state,  and  they  should 
be  continually  stirred,  if  the  bottom  of  the  vessel  containing 
them  be  liable  to  an  injurious  elevation  of  temperature. 

601.  When  substances  in  powder,  not  subject  to  injury 
from  an  occasional  high  temperature,  are  placed  upon  the 
sand-bath  to  dry,  they  should  be  covered  with  paper  (566) 
to  keep  out  dust.     Or  if  loose  covers  be  more  convenient,  a 
glass  bottom  (553),  or  another  basin,  will  answer  the  pur- 
pose ;  but  in  these  cases  the  cover  is  to  be  removed  now  and 
then,  to  allow  the  escape  of  vapour,  and  should  be  dried  be- 
fore being  replaced. 

602.  In  cases  of  desiccation,  it  is  frequently  required  to 
know  whether  all  the  water  that  can  be  dissipated  has  risen, 

•or  whether  vapour  be  still  passing  away.  A  very  excellent 
and  delicate  mode  of  determining  the  point  is  to  cover  the 
dish  with  a  cold  glass  plate  or  basin  ;  if  dimness  appear,  it 
shows  that  vapour  is  rising.  The  test-glass  must  sometimes 
remain  nearly  a  minute,  or  until  it  is  warm,  before  a  con- 
clusion may  be  drawn,  such  an  interval  being  necessary  to 
make  the  presence  of  vapour  visible  when  in  small  quantity. 
Powders,  supposed  to  be  hygrometric,  or  to  have  absorbed 
moisture  from  the  air,  may  be  heated  in  a  small  basin,  and 
tested  by  this  method,  and  the  dryness  of  extracts,  and  many 
other  bodies,  may  be  ascertained  in  a  similar  manner. 

6031  Evaporations  are  frequently  performed  on  a  small 
scale  (943),  and  will  occasionally  be  carried  on  in  capsules 
or  on  small  plates  (1348),  or  in  fragments  of  Florence 
flasks;  and  the  spirit-lamp  (199),  the  sand-bath  (173),  and 
the  hot  plate  of  the  table-furnace  (171),  will  be  in  constant 
requisition  as  sources  of  heat. 

604.  The  importance  of  a  current  of  air  in  facilitating 
evaporation,  generally,  by  removing  the  moist  atmosphere 
and  allowing  fresh  vapour  to  rise  with  greater  facility,  is  so 
well  known,  that  it  will  be  needless  to  urge  its  application 
in  every  case  where  it  can  do  no  harm,  and  is  on  other  ac- 
counts admissible. 

605.  A  warm  air-chamber,  when  it  can  be  obtained,  is 
highly  useful  for  desiccation,  evaporation,  and  similar  pur- 
poses.    It  should  not  consist  merely  of  a  cavity  or  closet, 
but  should  admit  of  a  thorough  draught  of  air.     One  that 


41 
DESICCATION WARM  AIR-CHAMBER.  281 

has  been  constructed  by  Mr  Goopet  is  the  best  in  its  prin- 
ciple, and  most  convenient  in  its  application,  in  the  labora- 
tory of  research,  with  which  I  am  acquainted.  It  consists 
of  an  inclosed  space  placed  near  the  furnace,  so  as  to  re- 
ceive some  warmth  from  it,  but  rendered  fully  efficacious  in 
the  operations  for  which  it  is  intended,  by  a  current  of  hot 
air  traversing  it.  This  air  is  heated  by  passing  round  an 
iron  plate  aVthe  back  of  the  furnace,  and  enters  the  air- 
chamber  at  the  top ;  another  passage  for  its  exit  com- 
mences at  the  bottom,  in  a  situation  as  far  as  possible  from 
the  former  opening,  and  is  continued  until  it  joins  the  flue 
of  the  furnace  at  a  convenient  place.  Thus  the  hot  air  is 
made  to  descend,  and  spread  through  the  chamber  by  the 
draught  of  the  flue.  A  damper  is  inserted  for  the  conveni- 
ence of  opening  or  closing  the  communication  at  pleasure, 
and  entrance  is  gained  to  the  chamber  by  a  door  which 
closes  accurately  and  is  fastened  by  a  button. 

606.  A   warm  air-chamber  may  be  made  of  brick-work, 
metal,  or  even  wood,  and  may  be  placed  in  any  convenient 
part  near  the  furnace.     An  excellent  situation   for  it  in  the 
table-furnace  (169,  172)  exists  within  the  walls  and  beneath 
the  fhie,  where  the  arrangements  necessary  for  heating  the 
current  of  air  will  be  ready  and  obvious.     Projecting  spikes 
should  be  fastened  into  one  or  two  sides  of  these  chambers,  to 
hold  a  tin  plate  or  a  board,  to  form  a  temporary  shelf  when 
required. 

607.  Precipitates, filters,  and  other  moist  substances4  put  in- 
to such  a  chamber,  are  readily  and  safely  dried.     The  hot  air 
causes  evaporation  of  the  water,  whilst  the  current  removes 
the  rising  vapour.     The^chamber  is  very  useful  in  effecting 
the  slow  evaporation  of  liquids  (565,  568),  and  also  for  hot 
nitrations  (544),  when  the  entering  current  of  air  is  of  a  tem- 
perature sufficient  for  the  purpose. 

608.  In  cases  of  necessity,  a  similar  chamber  may  be  made 
by  passing  the  stream  of  heated  gaseous  products  from  a  small 
crucible  furnace  (269)  into  one  side  of  a  box,  and  allowing  an 
aperture  on  the  other  side,  or  at  the  bottom,  for  its  exit : 
but  as  dust  may  pass  with  the  air,  it  is  necessary  that  the 

2   L 


282  DESICCATION — BY  ABSORBENTS. 

.    % 

substances  to  be  evaporated  or  dried  be  covered  with  bibu- 
lous paper  (566).  An  Argand  lamp  (270)  may  be  applied 
in  the  same  manner  as  the  furnace  ;  and  in  this  case  even  a 
band-box  may  be  used  for  \Jie  chamber,  the  hot  air  entering 
by  a  two-inch  tube  with  a  funnel  termination  at  one  side 
(1342),  and  passing  out  by  an  opening  at  the  other  side,  or 
in  the  bottom.  The  chamber  should  not  be  too  large  in 
proportion  to  the  lamp,  but  of  such  dimensions >as  to  be  re- 
tained at  a  considerable  temperature,  and  then  the  water 
formed  during  the  combustion  of  the  oil  will  not  be  deposit- 
ed :  and  though  it  will  diminish  the  drying  power  of  the  air, 
in  cases  of  evaporation,  it  will  still  leave  it  in  a  very  useful 
state. 

61)9.  Where  filters  with  precipitates  upon  them  are  to 
be  dried,  one  useful  method  is  to  put  them  upon  a  clean 
tin  plate,  with  a  piece  of  filtering  paper  intervening  or  not, 
according  to  circumstances,  and  placing  the  plate  over  the 
sand-bath  at  a  part  where  its  temperature  may  be  sufficient- 
ly raised.  The  sand  may  be  removed  from,  or  arranged 
over  the  bottom  of  the  bath  at  this  part,  so  as  to  regulate 
the  heat  communicated  to  the  tin  plate,  which  should  never 
be  such  as  to  char  paper ;  and  at  other  times,  when  no  fur- 
nace or  sand-bath  is  in  action,  the  plate  may  be  heated  by 
an  oil-lamp  placed  beneath  (212, 270).  These  arrangements 
will  often  be  found  very  useful. 

610.  Precipftates  which  have  been  separated  or  washed  in 
a  filter  may  have  a  considerable  quantity  of  the  fluid  remov- 
ed from  them  by  being  placed  upon  an  absorbent  body.  A 
large  mass  of  chalk  with  a  flat  surface  is  exceedingly  useful 
for  this  purpose,  when  the  fluid  to  be  removed  is  water  ;  and 
a  sheet  or  two  of  filtering  paper  folded  up  into  several 
thicknesses  may  be  used  when  the  fluid  is  acid,  alkaline,  or 
saline.  When  the  filter  with  its  contents  is  to  be  transfer- 
red, it  should  first  be  loosened  at  the  sides,  by  inclining  the 
funnel,  and  then  either  lifted  out  by  the  edges  and  laid  upon 
the  absorbent  body,  or  if  too  heavy  to  admit  safely  of  such  a 
method,  it  should  be  slipped  out  of  the  funnel  by  inclining 
the  latter,  its  motion  being  assisted  at  the  same  time  by  a 
slight  pull.  If  the  filter  be  a  simple  one  (533),  the  side  thus 


\ 


DESICCATION COLLECTING    FROM    KILTER.  283 

laid  on  the  absorbent  surface  should  be  that  which  is  single 
and  then  the  folds  are  easily  opened,  anjl  the  filter  with  its 
contents  laid  out.  If  the  chalk  be  used,  it  should  be  sep- 
arated from  the  filter  by  an  intervening  piece  of  bibulous 
paper. 

611.  After  a  time  proportionate  to  the  'nature  and  quan- 
tity of  the  precipitate,  the  latter  will  be  found  dried  to  a 
certain  degree.     Many  precipitates  admit  of  the  operation 
being  hastened  by  folding  ihe  filter  over  them,  laying  several 
folds  of  bibulous  paper  upon  it,  and  applying  pressure  with 
the  hand.     When  the  paper  has  become  wetted,  dry  paper 
is  to  replace  it,  and  the  operation  renewed.     This  expedient 
must  not  be  adopted  unless  the  precipitate  have  so  much 
consistency  as  to  bear  the  pressure  without  being  forced  out 
at  the  edge  of  the  filter.     After  an  operation  of  this  kind, 
the  filter  with  it's  contents  may  be  removed  to  the  warm  air 
chamber  (605),  or  the  hot  plate  (609),  and  dried  in  the  usual 
manner. 

612.  The  solid   contents  of  small  filters  (546)   are  fre- 
quently dried  with  advantage  in  the  above  manner  between 
folds  of  paper.     It  often  happens  that  the  substance,  though 
in  small  quantity,  is  rare  or  valuable  ;  in  which  case  the  fol- 
lowing method  nrray  be  adopted  for  the  prevention  of  loss. 

After  being  pressed  once  or  twice,  it  will  form  a  layer 
within  a  fold  of  the  filter,  the  paper  being  above  and  beneath, 
and  adhering  slightly.  Fold  one  edge  of  the  paper  quite 
back,  and  then  pull  it,  stripping  as  it  were  the  paper  off  the 
precipitate  ;  this  may  be  done  without  disturbing  the  moist 
cake  of  solid  matter  :  then  double  the  filter  with  its^ontents, 
making  the  fold  pass  through  the  middle  of  the  precipitate, 
by  which  it  will  also  be  doubled  up,  and  being  pressed  a 
little,  will  so  far  adhere  that  the  paper  may  be  bent  back  and 
stripped  off*  as  before,  without  disturbing  the  substance ;  in 
this  way  the  cake  is  reduced  to  half  its  .original  extent,  but 
doubled  in  thickness,  and  by  repeating  the  operation,  the 
precipitate,  however  small  in  quantity,  may  be  collected 
from  the  different  parts  of  the  filter  into  one  compact  por- 
tion. 

613.  Before  quitting  the  subject  of  desiccation,  it  may  be 
remarked,  that  moistened  crystals  or  other  substances  in 


284  DRAINING   CRYSTALS COLOURED  TESTS. 

small  fragments,  are  frequently  put  into  funnels  to  drain, 
and  that  the  required  effect  is  hastened,  and  also  carried  to 
a  greater  extent,  than  it  otherwise  would  be,  by  inserting  a 
folded  slip  of  filtering  paper  into  the  neck  of  the  funnel,  so 
that  its  upper  end  may  touch  the  bottom  of  the  collection  of 
crystals,  and  its  lower  project  a  little  beyond  the  funnel. 
Thus  situated,  it  enables  the  liquor  to  drain  away  to  a  greater 
extent  than  would  otherwise  take  place.  ** 

614.  M.  Robinet^  has  very  much  improved  this  process 
of  draining  crystals,  by  passing  a  current  of  air  through 
them.  If  the  crystals  be  put  into  a  funnel  with  its  neck  ob- 
structed by  a  ball  of  cotton  wool,  and  the  funnel  be  then 
fixed  in  one  aperture  of  a  double-mouthed  bottle,  whilst  a 
tube  is  attached  to  the  other,  air  may  be  drawn  by  the  tube 
through  the  funnel  and  its  contents,  into  the  bottle,  and  will 
carry  with  it  the  mother-water,  or  adhering  moisture,  in  such 
an  effectual  manner  as  perfectly  to  cleanse  the  most  silky 
crystals. 


SECTION  XII. 

COLOURED  TESTS— NEUTRALIZATION. 

I 

615.  THOSE  very  important  chemical   substances,  acids 
and  alkalies,  in  a  free  state,  possess  the  power,  even  in  very 
small   quantity,  of  effecting  certain    general   and    regular 
changes  in  the  tints  of  some  vegetable  colours.     The  dis- 
tinctness of  the  change  and  facility  with  which   it  is  pro- 
duced have  occasioned  the  colours  to  be  used  as  tests  of  the 
presence  of  these  bodies  when  uncombined  or  in  excess,  and 
they  are  now  of  such  constant  service  as  to  be  indispensable  in 
the  laboratory.     They  are  prepared  for  use  in  a  state  of  so- 
lution, or  fixed  upon  paper;  the  preparations  being  called 
test  solutions,  or  test  papers. 

616.  The  only  substance  of  the  kind  perhaps  worth  keep- 

*  Annals  of  Philosophy,  New  Series,  xii.  460. 


KKI)   CAKKAGE— LITMUS TURMV.RIC.  285 

ing  in  solution  is  an  acid  infusion  of  red  cabbage.  For  its 
preparation,  one  or  more  red  cabbages  should  be  cut  into 
strips,  and  boiling  water  poured  upon  the  pieces;  a  little 
dilute  sulphuric  acid  is  to  be  added,  and  the  whole  well 
stirred  :  it  is  then*  to  be  covered  and  kept  hot  as  long  as 
possible,  or,  if  convenient,  should  be  heated  nearly  to  boil- 
ing for  an  hour  or  two  in  a  copper  or  earthen  vessel.  The 
quantity  of  water  to  be  added  at  first  should  be  sufficient  to 
•cover  the  cabbage,  and  the  sulphuric  acid  should  be  in  the 
proportion  of 'about  half  an  ounce  of  strong  oil  of  vitriol  by 
measure  to  each  good  sized  plant.  This  being  done,  the 
fluid  should  be  separated  and  drained  off,  and  as  much  more 
hot  water  poured  on  as  will  cover  the  solid  residue,  adding 
a  very  little  sulphuric  acid.  The  whole  is  to  be  closed  up, 
and  suffered  to  stand  until  cold,  and  then  the  liquid  poured 
off  and  added  to  the  former  infusion.  The  cabbage  may 
now  be  thrown  away.  The  infusion  is  to  be  evaporated  to 
one-half  or  one-third  its  first  bulk,  poured  into  ajar,  allowed 
to  settle,  and  the  clear  red  fluid  decanted  and  preserved  in 
bottles.  The  residue  may  have  water  added  to  it,  the  solid 
part  be  allowed  to  subside,  the  clear  liquor  drawn  off,  evapo- 
rated, and  added  to  the  former,  or  it  may  be  dismissed  al- 
together. This  solution  will  keep  for  a  year.  When  re- 
quired for  use,  the  acid  of  a  small  portion  of  it  should  be 
neutralized  by  caustic  potash  or  soda  (not  by  ammtfnia), 
when  it  will  assume  an  intensely  deep  blue  colour,  and  will, 
in  most  cases,  require  dilution  with  twelve  or  fourteen  parts 
of  water.  The  red  liquor  of  pickled  cabbage  will,  occasion- 
ally, answer  the  uses  of  the  solution,  and  is,  when  required  for 
service,  to  be  neutralized  in  a  similar  manner.* 

617.  Test  papers  are  far  more  advantageous  for  use  than 
liquids:  two  of  them  in  general  application  and  delicacy 
surpass  the  rest,  these  are  litmus  and  turmeric  papers.  For 
the  preparation  of  the  former,  some  good  litmus  is  to  be  rub- 

*  The  readiest  mode  of  preserving  red  cabbage  is  to  cut  it  into  small  pieces, 
dry  it  on  a  tray,  under  sand  placed  in  the  sun,  and  to  bottle  it  when  dry,  along 
with  a  portion  of  the  sand.  Cabbage  thus  prepared  remains  unaltered  for  many 
years,  and  forms  at  any  moment  with  hot  wate»  a  coloured  solution  as  beautiful 
as  can  be  obtained  from  the  fresh  leaves. — ED. 


28C  "LlTMUS-PAPERr-SELECTED. 

bed  to  powder  with  hot  water  in  a  mortar,  the  mixture  pour- 
ed into  an  evaporating  basin  or  a  flask,  and  water  added  until 
the  proportion  is  about  half-a-pint  for  each  ounce  of  litimus. 
It  is  to  be  covered  up  so  as  to  remain  warm  for  an  hour,  af- 
ter which  the  clear  liquor  is  to  be  decanted,  and  fresh  hot 
water  poured  on  to'  the  residue.  This  is  to  be  covered  up 
as  before,  suffered  to  stand,  and  the  liquid  evaporated.  The 
operation  is  to  be  repeated  a  second  time,  and  if  much 
colour  appears  to  be  removed,  even  a  third.  The  first  solu-# 
tion  is  to  be  kept  apart  from  the  second  and  third,  which 
may  be  mixed.  The  first  portion  will  not  require  evapora- 
tion, but  the  others  are  to  be  so  far  reduced  in  quantity,  that 
when  a  piece  of  filtering  paper  is  dipped  into  them,  and 
dried,  they  will  impart  to  it  a  blue  colour  of  sufficient  in- 
tensity for  use. 

618.  Paper  is  then  to  be  dipped  into  the  prepared  solu- 
tion.    The  paper  should  in  all  cases  be  bibulous,  and  not 
sized  (530),  so  that  fluid  dropped  upon  it  should  be  instant- 
ly absorbed.     Sized    paper  often   presents  a  fairer  tint  of 
colour  upon  the  surface,  but  is  by  no  means  so  delicate  as  a 
test.     The  paper  should  be  of  a  good  colour,  that  the  tint 
may  not  be  injured ;  of  sufficient  thickness  not  to  become 
almost  transparent  when  wet ;  and  particular  care  should  be 
taken  that  it  be  free  from  earthy  matter,  especially  carbonate 
of  lime,   and  alkalies.     It  may  be  examined  as  to  these 
points  in  the  manner  recommended  for  filtering  paper  (530). 

619.  The  paper  selected  should  be  cut  into  pieces  of  a 
size  convenient  to  be  dipped,  somewhat  less,  for  instance, 
than  half  a  sheet  of  post  paper.     The  litmus  solution  should 
be  poured  into  a  dish  or  soup-plate,  and  the  paper  should  be 
drawn  through  it  piece  by  piece,  in  such  a  manner  that  the 
fluid  may  be  in  contact  with  both  sides,  and  then  having 
been  held  to  drajn  a  few  seconds,  it  should  be  hung  on  lines 
of  thread  or  twine  to  dry,  in  a  convenient  place.     No  fumes 
of  acid  or  burning  charcoal  should  have  access  to  it,  for 
they  injure  the  colour ;  and  as  soon  as  the  paper  is  dry  it 
should  be  taken  down,  and  laid  together.     The  tint  ought 
to  be  a  full  blue,'or  if  light,  not  faint  or  undecided :  it  may 
be  judged  of  by  touching  a  piece  of  the  paper  with  a  very 


TURMERIC-PAPER PRESERVED.  287 

weak  acid,  and  observing  whether  the  red  colour  produced 
is  vivid,  and  a  strong  contrast  to  the  blue  tint  of  the  rest  of 
the  paper.  If  the  solution  should  have  been  made  so  dilute 
as  to  produce  too  weak  a  tint,  the  paper  may  be  dipped  a 
second  time,  but  this  is  to  be  avoided  if  possible,  as  it  in- 
volves a  second  exposure  to  the  air. 

620.  It  may  happen  from  the  suspension  of  fine  particles 
of  litmus  in  the  solution,  that  the  tint  is  not  so  clear  as  was 
required,  but  has  a  dusky  appearance.     This  is  unpleasant, 
buj  is  not  injurious;  the  fine  particles  of  litmus  testing  the 
presence  of  an  jrcid  nearly  as  well  as  the  stained  paper. 

621.  When  the  paper  has  acquired  its  proper  colour  and 
is  dry,  it  should  immediately  be  tied  up  closely  in  stiff  pa- 
per, and  preserved  from  the  air  and  light :  the  latter  injures 
and  destroys  its  colour,  and  the  former,  from  the  carbonic 
acid  and  other  occasional  substances  it  contains,  injures  the 
colour,  and  consequently  the  sensibility  of  the  paper. 

622.  Turmeric  paper  is  to  be  prepared  in  a  similar  man- 
ner.    A  hot  infusion  of  finely-bruised  or  coarsely-ground 
turmeric  is  to  be  made,  by  boiling  one  ounce  of  the  root  with 
ten  or  twelve  ounces  of  water  for  half  an  hour,  straining 
through  a  cloth,  and  leaving  the  fluid  to  settle  for  a  minute 
or  two.     The  liquid  should  be  of  such  strength  that  paper, 
when  dipped  into  it  and  dried,  should  acquire  a  fine  yellow 
colour.     The  paper  should  be  of  the  kind  before  described 
(618).     No  particular  care  is  required  during  drying,  rela- 
tive to  exposure  to  air,  except  that  acid  and  alkaline  fumes 
should  not  have  access,  as  they  may  transfer  injurious  mat- 
ter to  the  paper,  and  diminish  its  delicacy.     When  dry  it 
should  be  wrapped  up  and  preserved  with  care. 

623.  The  stock  of  test-papers  should  not  be  left  lying 
about  the  laboratory  for  general  use,  for  then  much  is  torn 
upr  carelessly  and  wasted,  arid  much  more  spoiled  by  floating 
fumes.     But  a  piece  of  each  should  be  cut  into  slips  about 
six  inches  in  length,  and  half  an  inch   in   width,  and  either 
put  into  a  stoppered  bottle,  with  dark  paper  pasted  round  it 
to  prevent  the  entrance  of  light,  or,  what  is  more  convenient, 
tied  up  in  a  case  of  cartridge  paper,  the  slips  projecting  about 


288  COLOURED  TEST-PAPERS  APPLIED. 

half  an  inch  at  each  end,  that  one,  either  of  litmus  or  of  tur- 
meric, may  be  "withdrawn  at  pleasure. 

624.  In  using  these  test-papersWith  a  fluid  suspected  to 
contain  free  acid  or  alkali ;  or,  knowing  that  one  of  these  sub- 
stances is  predominant,  to  ascertain  which  is  so,  all   that  is 
necessary  is  to  moisten  them   with  the  liquid,  and  observe 
th?  change:  if  the  fluid  be  acid,  the  blue  colour  of  the  lit- 
mus will  immediately  become  red;  if  alkaline,  the  yellow 
colour  of  the  turmeric  will  be  changed-  to  a  brown.     The 
moistening  may  b»  effected  by  dipping  the   paper  into  £he 
liquid,  but  a  better  method  is  to  touch  the  edge  of  the  slip 
with  a  rod  dipped  in  the  fluid  (374).     In  the  latter  case 
there  is  no  risk  of  contamination  to  the  fluid  from  the  pa- 
per, and  only  a  very  minute  quantity  of  the  liquid  is  used  at 
once. 

625.  These  trials  must  be  made  by  day-light;  artificial 
light  not  permitting  that  just  estimation  of  the  changes  by 
which  the  presence  of  a  small  excess  of  acid  or  alkali  is  to  be 
determined.     As  the  proportion  of  free  acid  or  alkali  dimin- 
ishes, the  intensity  of  the  new  tint  produced  upon  the  paper 
is  also  diminished,  and  when  in  very  small  quantity,  it  requires 
considerable  attention  before  a  decision  can  be  arrived  at. 
The  test  paper  should  occasionally  be  touched  with  pure 
water  in*the  immediate  neighbourhood  of  the  part  where  the 
solution  has  been  applied;  for  any  change  in  appearance  that 
may  have  occurred,  not  due  to  mere  moistening,  is  then  read- 
ily perceived. 

626.  Although  acid  is  generally  tested  for  by  litmus  paper, 
and  alkali  by  turmeric  paper,  yet  the   former  is  sometimes 
used  advantageously  for  the  latter  purpose,  being  first  slightly 
reddened  either  by  exposure  to  the  air,  or  by  momentary  con- 
tact with  muriatic  acid  fumes.     When  the  paper  thus  modi- 
fied is  used  instead  of  turmeric  paper,  to  detect  a  free  alkali, 
that  substance  is  indicated  by  the  restoration  of  the  original 
blue  colour.     Litmus  paper  is  best  slightly  reddened  for  this 
use,  by  putting  a  drop  or  two  of  muriatic  acid  into  a  large 
jar,  allowing  it  to  stand  a  few  minutes,  and  then  bringing 
the  paper  towards  the  mouth  of  the  jar,  or  carefully  placing 


ALKALI  IN  LITMUS NEUTRALIZATION.  289 

it  within;  so  soon  as  the  blue  tint  has  become  slightly  redden- 
ed, the  paper  should  be  removed  for  use.  If  too  much  acid 
be  imparted  to  the  paper,  the  delicacy  of  its  indications  is 
injured,  because  of  the  greater  quantity  of  alkali  required  to 
neutralize  the  acid,  and  restore  the  blue  colour.  For  the 
same  reason  a  paper  free  from  alkali  or  carbonate  of  lime 
has  been  recommended  for  the  preparation  of  these  tests 
(618),  for  these  impurities  combining  with  a  minute  portion 
of  acid,  neutralize  it,  and  thus  prevent  that  delicacy  of  in- 
dication which  the  test  paper  ought  and  may  be  made  to 


627.  Litmus  contains  a  portion  of  alkali,  and  so  also  does 
litmus-paper,  in  consequence  of  which  it  becomes  insensible 
to  liquids  very  weakly  acid,  when  applied  in  the  small  quan- 
tities above  directed,  because  the  acid  present  in  the  drop  is 
neutralized  by  the  alkali  of  the  paper,  and  therefore   has  no 
effect  on  the  colour:   but  in  these  cases  there  can  be  very 
little  free  acid,  and  if  absolute  certainty  as  to  its  existence, 
or  not,  be  required,  it  is  then  better   to  cut   some   little 
squares  of  the  test-paper,  the  one-tenth  or  one-twentieth 
of  an  inch  in  size,  to  put  one  of  these  into  the  liquid,  and 
move  it  from  place  to  place.     If  there  be  the  smallest  trace 
of  free  acid  present,  the  alkali  of  the  paper  is  quickly  neu- 
tralized, and  then  the  blue  colour  changed  to  red. 

628.  Neutralizations  are  best  effected  with  the  assistance 
of  heat,  especially  if  a  carbonate  be  used,  or  if  precipitation 
occur  during  the  operation.     The  carbonic  acid  in  the  first 
case  is  dissipated,  and  in  the  latter  the  combination  is  more 
rapidly  and  perfectly  effected.     Evaporating  basins  (369) 
are  highly  useful  for  these  purposes,  their  contents  being 
easily  stirred,  and  the  rod  used  for  that  purpose  also  applied 
to  moisten  the  test-paper  when  required.     The  solution  to 
be  neutralized  should  not  be  very  strong,  and  the  substance 
added  should  be  diluted  (511),  upon  approaching  the  point 
of  neutralization,  if  it  be  accurately  required,  for  the  reasons 
before  given.     The  successive  trials  on  the  test  paper  should 
be  made  down  one  edge,  and  occasionally  contrasted  with 
the  effect  produced  by  water  (625).     On  very  delicate  oc- 

2  M 


290  PRECIPITATION TEST FALLACIES. 

casions  this  comparative  trial  should  be  made  with  hot 
water,  heated  in  a  small  basin  by  the  side  of  the  larger  one 
containing  the  solution.  Great  care  should  be  taken  that 
the  paper  be  not  brought  into  contact  with  acid  fumes  dur- 
ing the  trial;  or  much  error  ma^  inadvertently  be  occa- 
sioned. 

629.  Sometimes  precipitations  are  to  be  effected  in  neu- 
tral   solutions,  by  the  addition  of  an  alkali,  or  an  alkaline 
carbonate,  it  being  desirable  to  have  as  little  excess  of  the 
latter  as  possible.    Turmeric  paper  is  then  required,  and  the 
operation  should  be  performed  by  heat  as  before  mentioned  ; 
but  instead  of  adding  the  precipitant  gradually  to  the  whole 
of  the  solution,  until  slight  indications  of  an  alkali  in  excess 
appear,  it  is  better  to  reserve  a  small  portion  of  the  solution, 
and  then  rapidly  rendering  the  rest  slightly  alkaline,  after- 
wards to  add  the  small  portion  by  degrees,  testing  with  the 
turmeric  paper  until  the  point  is  as  nearly  attained  as  re- 
quired.    The  small  remaining  part  may  then  be  precipitated, 
by  adding  alkali  carefully  and  continuing  to  test  it,  and  finally 
adding  it  to  the  larger  portion. 

630.  There  are  many  substances  which  affect  the  colour 
of  test  papers,  and  especially  of  turmeric  paper,  either  inde- 
pendently of  the  free  acid  or  alkali  they  contain,  or  with  ap- 
pearances different  to  those  described  ;  which,  if  unknown, 
might  sometimes  lead  to  error.     Solution  of  boracic  acid, 
whether  strong  or  weak,  gradually  changes  turmeric  paper, 
producing  a  tint  resembling  that  occasioned  by  an  alkali;  and, 
if  previously  mixed  with  the  common  acids,  produces  still 
stronger  tints  of  red  and  reddish-brown.  The  borates  occasion 
the  same  effect,  especially  when  mixed  with  acids,  and  some 
of  the  tints  very  much  resemble  those  produced  by  alkalies. 
Strong  oil  of  vitriol  and  muriatic  acid  gas  redden  turmeric 
paper,  but  the  redness  is  removed  by  the  addition  of  water. 
Ammoniacal  gas,  on  the  contrary,  does  not  redden  turmeric 
paper,  unless  there  be  sufficient  water  present  in  the  paper  to 
dissolve  the  gas.     The  salts  of  iron,  tin,  and  uranium,  the 
muriates  of  zirconia,  zinc,  antimony,  and  manganese,  and  the 
nitrate  of  bismuth,  when  in  moderately  strong  solution,  pro- 


ALKALIMETRY ALKALIMETER  MADE.  291 

duce  tints  in  turmeric  paper,  resembling  those  occasioned  by 
excess  of  alkali*.  It  should  be  remarked,  for  the  instruction 
of  those  who,  meeting  with  a  difficulty  of  this  kind,  may  re- 
sort to  paper  stained  yellow  by  rhubarb,  that  it  also  is  affect- 
ed in  the  same  way,  though  not  so  generally,  but  that,  with 
particular  care,  it  is  a  very  excellent  test  of  the  presence  of 
alkalies. 

631.  Alkalimetry  at  present  consists  in  an  estimative  pro- 
cess, dependant  upon  neutralization  and  the  use  of  the  test 
papers  just  described;  the  object  being  to  ascertain  the 
quantity  of  free  alkali  or  of  carbonate  contained  in   any  im- 
pure specimen,  as  for  instance,  in  that  produced  by  the  first 
rough  process  for  their  preparation.     Descroisilles  first  re- 
sorted to  neutralizing  power  for  this  purpose,  but  the  extent 
to  which  the  application  has  been  improved  by  chemists 
since  his  time  may  be  seen  in  modern  worksf. 

632.  Let  a  tube,  closed  at  one  end,  of  about  three-fourths 
of  an  inch  internal  diameter  and  nine  inches  and  a  half  in 
length,  have  1000  grains  of  water  weighed  into  it;  then   let 
the  space  it  occupies  be  graduated  into  100  equal  parts,  by 
the  processes  formerly  described  (129,  &c.),  and  every  ten 
divisions  numbered  from  above  downwards.     At  23.44  parts, 
or  76.56  parts  from  the  bottom,  make  an  extra  line  a  little  on 
one  side,  or  even  on  the  opposite  side  to  the  graduation,  and 
write  at  it  with  the  scratching  diamond  (128)  Soda;  lower 
down  at  48.96  parts,  make  another  line,  and  write  potash; 
still  lower  at  54.63  parts,  a  third  line  marked  carb.  soda;  and 
at  65  parts  a  fourth,  marked  carb.  potash.     It  will  be  ob- 
served that  portions  are  measured  off,  beneath  these  marks, 
in  the  inverse  order  of  the  equivalent  numbers  of  these  sub- 
stances, and  consequently  directly  proportionate  to  the  quan- 
tities of  any  particular  acid,  which  will  neutralize  equal 
weights  of  the  alkalies  or  their  carbonates.     As  these  points 
are  of  great  importance,  it  will  be  proper  to  verify  them  by 
weighing  into  the  tube  first  350,  then  453.7,  then  510.4,  and 

*  Quarterly  Journal  of  Science,  xiii.  315,  xiv.  234. 

t  Ure'a  Dictionary  of  Chemistry,  introduction,  p.  xiii.     Henry's  Elements  of 
Chemistry,  eighth  edition,  ii.512. 


292          THE  ACID  PREPARED — THE  ALKALI. 

lastly  765.6  grains  of  water,  which  will  correspond  with  the 
marks  if  they  are  correct.  Or  the  graduation  may  be  laid 
down  from  the  surface  of  the  four  portions  of  fluid  when 
weighed  in  without  reference  to  where  they  fall  upon  the  ge- 
neral scale.  The  tube  is  now  completed,  except  that  it 
should  be  observed  whether  the  aperture  can  be  perfectly 
and  securely  covered  by  the  thumb  of  the  left  hand,  and  if 
not,  or  if  there  be  reason  to  think  it  not  ultimately  secure, 
then  it  should  be  heated  and  contracted  until  sufficiently  small. 
(Sect,  xix.) 

633.  Diluted  sulphuric  acid  must  now  be  prepared  to  be 
used  with  the  tube.     When  a  specific  gravity  of  1.1268,  it 
will  be  very  nearly,  if  not  accurately,  of  the  strength  re- 
quired; and  this  may  be  obtained  by  mixing  one  part  by 
weight  of  oil  of  vitriol  of  specific  gravity  1.82,  with  four 
parts  of  water.     If,  when  cold,  the  specific  gravity  of  this 
diluted  acid  be  as  above  mentioned  1.1268,  it  must  be  near- 
ly, if  not  exactly,  of  the  strength  required  ;  but  before  being 
admitted  into  use,  should  be  examined  experimentally.     As- 
suming it,  however,  as  being  absolutely  correct,  it  will  be 
found  that  a  quantity  measured  into  the  tube  up  to  any  one 
of  the  four  marks  described,  is  sufficient  to  neutralize  100 
grains  of  the  dry  alkali  or  carbonate  set  down  at  the  mark  ; 
consequently,  if  water  be  added  in  the  tube,  thus  filled  up 
to  any  one  of  the  marks,  until  the  100  parts  are  full,  and  the 
whole  uniformly  mixed,  one  part  of  such  diluted  acid  will 
neutralize  one  grain  of  the  alkali  or  carbonate  named  at  the 
mark,  up  to  which  the  tube  was  first  filled  with  the  acid  of 
specific  gravity  1.1268. 

634.  When  a  specimen  of  potash,  barilla,  or  kelp,  is  to 
be  examined  by  this  instrument,  100  grains  are  to  be  weigh- 
ed out,  dissolved  in  warm  water,  filtered,  the  insoluble  por- 
tion washed,  and  the  solution  added  to  the  rest ;  by  this 
process  the  alkali  will  be  separated  from  carbonate  of  lime, 
or  other  insoluble  matters,  which  otherwise  might  cause  er- 
rors in  the  estimation.     The  alkaline  solution  is  to  be  put 
into  a  basin  on  the  sand-bath,  and  then  the  tube  and  acid 
prepared.     For  this  purpose  some  of  the  acid,  of  specific 
gravity  1.1268,  is  to  be  poured  into  the  tube  until  it  rises  up 


ALKALIMETRY — THE  PROCESS.  293 

to  the  mark  indicating  the  substance  to  be  tested  for ;  pot- 
ash or  carbonate  of  potash  for  the  potash  or  pearlash  of 
commerce,  and  soda  or  carbonate  of  soda  for  barilla  or  kelp : 
then  water  is  to  be  added  carefully  (402),  until  the  hundred 
parts  are  filled,  and  closing  the  tube  with  the  finger,  its 
contents  are  to  be  perfectly  agitated  and  mixed. 

635.  The  alkali  in  the  basin  is  now  to  be  neutralized  with 
the  acid  in  the  tube.     After  having  once  placed  the  thumb 
of  the  left  hand  over  the  aperture  of  the  tube,  it  is  not  to  be 
again  removed ;  but  inverting  the  tube  by  turning  the  hand 
so  that  the  thumb  and  the  mouth  of  the  tube  are  downwards, 
the  acid  is  to  be  let  out  gradually  into  the  alkaline  solution, 
by  relaxing  the  thumb  and  admitting  a  succession  of"  small 
bubbles  of  air ;  the  hot  solution  beneath  is  to  be  continually 
stirred,  so  as  to  mix  the  acid  instantly  with  the  whole,  and 
the  operator  must  proceed  with  increased  caution  as  the 
point  of  neutralization  is  approached.     Very  small  quanti- 
ties of  the  acid  may  be  added,  by  slightly  relaxing   the 
thumb  so  as  to  permit  a  minute  quantity,  less  than  a  drop, 
to  flow  to  its  extremity,  and  touching  it  with  the  glass  rod ; 
the  final  adjustment  may  thus  be  made  more  accurately,  than 
by  dropping  the  acidTrom  the  lip  of  the  tube.     The  process 
must  be  carried  on  until  the  alkali  is  found  by  the  test  pa-, 
pers  to  have  been  exactly  neutralized  (625,  627):  then  the 
tube  must  be  inverted,  the  thumb  removed,  drawing  its  un- 
der surface  over  the  edge  of  the  tube,  so  as  to  leave  as  much 
as  possible  of  the  fluid  that  otherwise  might  adhere  to  it, 
and  having  allowed  the  sides  to  drain,  it  must  be  observed 
how  many  parts  of  acid  have  been  used,  the  number  of 
which  will  indicate  the  number  of  grains  of  the  alkali  or 
carbonate,  contained  in  the  100  grains  of  the  impure  alkali 
operated  with. 

636.  With  respect  to  the  proper  strength  of  the  acid 
(633),  it  is  to  be  examined  in  the  following  manner :  crys- 
tals of  bi-carbonate  of  potash  are  to  be  fused  in  a  platinum 
crucible,  the  fluid  poured  out  upon  a  clean,  cold  metal  plate, 
and  a  piece  of  the  resulting  solid,  estimated  to  be  70,80,  or 
100  grains,  weighed  in  water  (72)  ;  in  this  way  a  known 
weight  of  pure  carbonate  of  potash  will  be  obtained  in  solu- 
tion.    The  solution  is  then  to  be  diluted,  heated,  and  neu- 
tralized by  acid  from  the  tube  diluted  as  before  described 


294  ALKALIMETRY — VERIFICATION  OP  THE  ACID. 

(633),  from  the  mark  of  carbonate  of  potash.  If  it  be  found 
that  as  many  parts  of  the  acid  have  been  used  as  of  grains 
of  the  carbonate  weighed  out,  the  acid  is  of  proper  strength  : 
if  more  acid  has  been  used,  it  is  too  weak,  if  less  has  been 
sufficient,  it  is  too  strong.  Suppose  for  instance  that  100 
grains  of  the  salt  (fused  carbonate  of  potash)  had  been 
used,  and  that  90  parts  of  the  acid  were  sufficient ;  then 
these  90  parts  ought  to  have  occupied  the  100,  and  conse- 
quently the  100  parts  contain  one-tenth  too  much  acid,  in 
consequence  of  the  experimental  acid  itself  containing  one- 
tenth  more  than  it  ought  to  do.  Hence  the  latter  must  be 
diluted  with  such  a  quantity  of  water  as  will  make  nine 
volumes  into  ten,  or  by  one-ninth  its  volume ;  for  as  the  90 
parts  used  are  to  the  100  parts  they  ought  to  have  occupied, 
so  is  any  number  of  parts  by  volume  of  the  acid  under  trial, 
to  the  number  of  parts  which  it  ought  to  occupy.  The  dif- 
ference between  the  two  last  numbers  will  give  the  quantity 
of  water  in  volumes,  to  be  added  to  the  acid  expressed  by 
the  first  of  them,  in  order  to  correct  it  and  make  it  of  proper 
strength.  On  the  contrary,  if  it  were  found  that  the  100 
parts  were  insufficient,  and  that  10  parts  more  of  similar  acid 
were  required,  then  there  is  too  much  water  by  one-eleventh 
of  the  whole  in  bulk,  the  correction  for  which  would  be  one- 
tenth  more  of  the  35  parts  of  acid  put  into  the  tube  up  to 
the  mark  65  carb.  potassa.  This  tenth  is  3.5  parts,  but  as 
only  a  fifth  of  that  or  0.7  parts  is  acid,  therefore  0.7  parts  by 
weight  of  the  same  oil  of  vitriol  that  was  used  before  must  be 
added  for  every  35  parts  of  the  mixed  acid.  The  correction 
in  any  other  case  may  be  easily  made,  by  considering  that 
the  number  of  parts  over  a  hundred  which  are  necessary  to 
saturate  the  100  grains  of  carbonate  of  potash,  are  propor- 
tionate to  the  quantity  of  oil  of  vitriol  which  must  be  added 
to  bring  the  experimental  acid  to  proper  strength:  thus  if 
136  parts  of  the  diluted  acid  were  used,  then  thirty-six-hun- 
dreths  more  of  the  weight  of  oil  of  vitriol  already  used  must 
be  added  ;  and  the  quantity  of  oil  of  vitriol  that  was  added  at 
first  being  known  to  be  one-fifth  by  weight  (633),  the  addi- 
tional quantity  required  is  easily  ascertained.  These  cor- 
rections are  not  strictly  accurate,  but  sufficiently  so  to  meet 


ALKALIMETRY PRECAUTIONS.  295 

even  the  exaggerated  cases  put  of  a  difference  of  10  parts,  and 
to  bring  it  within  the  limit  of  errors  of  experiment. 

637.  Sometimes  instead  of  using  test  papers,  a  little  of 
the  neutralized  blue  cabbage  liquor  (616),  or  of  infusion  of 
litmus  may  be  put  into  the  alkaline  solution  ;  the  former  im- 
mediately assumes  a  green  tint :  and  by  attending  to  the 
change  effected  by  the  addition  of  the  acid,  and  noticing  the 
point  when  blueness  is  again  restored  to  the  cabbage-colour, 
or  when  the  litmus  becomes  reddened,  the  indication  of  neu- 
trality is  sufficiently  evident  and  accurate  for  general  pur- 
poses.    The  test  by  papers  is,  however,  more  precise. 

638.  Some  of  the  impure  sources  of  potash  and  soda  used 
in  the  arts  contain,  amongst  other  substances,  sulphuret  and 
sulphite  of  alkali.     Both  these  occasion  errors  in  the  mode 
of  estimation  above  described;  to  obviate  which  MM.  Wel- 
ter and  Gay  Lussac*  advise,  that  after  the  soluble  parts 
have  been  separated  by  water,  a  little  chlorate  of  potash 
should  be  added  to  them,  the  whole  evaporated  and  heated 
to  redness.     This  converts  the  sulphuret  and  sulphite  into 
neutral  sulphate,  and  then  upon  redissolving  the  whole,  the 
caustic  and  carbonated  alkali  may  be  ascertained  as  before 
described. 

639.  A  process  of  neutralization,  quite  the  same  in  prin- 
ciple, may  be  adopted  for  the  purpose  of  estimating  the 
strength  of  acids,  but  from  circumstances  it  is  not  often 
used,  and  being  easily  comprehended  from  the  above  direc- 
tions, claims  no  further  notice  here.     Acetic  acid  is  at  pres- 
ent the  substance  which  most  frequently  requires  some  such 
estimation  as  the  above,  both  because  its  specific  gravity 
varies  very  little  with  its  strength,  and  because  it  is  much  in 
use  in  the  arts  in  an  impure  state.     Dr.  Paris  has  pointed  out 
the  exact  agreement  between  the  equivalents  of  acetic  acid 
and  carbonate  of  lime,  and  has  proposed  to  estimate  the 
strength  of  this  acid,  by  allowing  it  to  act  upon  a  known 
weight  of  fragments  of  carbonate  of  lime,  and  ascertaining 
the  quantity  dissolved,  which  will  at  once  express  the  quan- 
tity of  pure  acid  present.     Vinegar,  however,  or  impure 

*  Annales  de  Chimie,  xiii.  212. 


296  AC1DIMETRY MINERAL  ACIDS. 

acetic  acid  is  not  very  readily  neutralized  by  pieces  of  car- 
bonate of  lime. 

640.  In  the  same  manner  muriatic,  nitric,  and  any  other 
acid,  which  forms  a  neutral  soluble  salt  with  lime,  and  has 
had  its  equivalent  number  well  ascertained,  may  be  estimat- 
ed, and  its  strength  become  known.  Thus  let  500  grains  of 
the  acid  be  put  into  a  basin  or  flask  with  100  grains  of  mar- 
ble in  fragments,  and  after  the  first  effervescence  is  over, 
warmed,  and  the  neutrality  ascertained  ;  the  solution  is  then 
to  be  poured  off,  and  the  remaining  pieces  of  marble  washed, 
dried,  and  weighed.  The  number  of  grains  of  carbonate  of 
lime  dissolved  in  muriatic  acid  multiplied  by  0.74,  indicate 
the  number  of  grains  of  dry  acid  by  which  it  has  been 
dissolved  ;  and  the  number  dissolved  in  nitric  acid  multipli- 
ed by  1.08,  also  represent  the  equivalent  of  dry  nitric  acid, 
or  the  quantity  present  in  the  solution  submitted  to  experi- 
ment. 


SECTION  XIII. 
CRUCIBLE  OPERATIONS— FU  SION— REDUCTION. 

641.  OPEN  vessels,  intended  to  receive  bodies  to  be  sub- 
jected to  high  temperatures,  have  received  the  name  of  cru- 
cibles.    They  are  very  various  in  form  and  material,  both  for 
the  sake  of  economy  and  to  fit  them  for  peculiar  uses.     By 
far  the  greater  number  are  formed  of  earthen  ware  ;  they  are 
cheap,  they  resist  a  high  temperature,  and  also  the  action  of 
most  bodies  which,  from  their  fixedness,  admit  of  or  require 
the  application  of  heat.    They  must,  however,  be  distinguish- 
ed from  each  other. 

642.  Ordinary  English  crucibles  are  easily  scratched  by  a 
knife  or  glass,  and  break  with  a  granular  crumbling  fracture. 
They  are  useful  for  many  common  purposes,  may  be  had  of 
a  triangular  or  circular  form,  with  covers  of  the  same  materi- 
al, and  are  cheaper  than  any  others.     They  will  bear  a  bright 


CRUCIBLES HESSIAN CORNISH.  297 

red  heat,  but  will  not  resist  a  very  high  temperature;  for  in 
it  they  soften  and  froth,  and  frequently  occasion  the  loss  of 
their  contents.  In  consequence  of  their  approach  to  fusibil- 
ity when  hot,  fluxes  render  them  quite  fusible,  for  which 
reason  they  will  not  retain  these  agents  long.  The  latter 
find  rapid  entrance  and  access  to  the  interior  in  consequence 
of  the  porosity  and  softness  of  the  vessels,  which,  of  course, 
allow  easy  penetration  by  the  fluid  :  after  being  heated  for 
a  short  time  with  a  coloured  flux,  and  then  cooled  and  bro- 
ken, the  extent  to  which  these  agents  penetrate  them  may  be 
readily  observed. 

643.  Hessian  crucibles  very  far  surpass  the  common  Eng- 
lish vessels  in  resistance  of  high  temperatures  and  the  action 
effluxes.     When  powerfully  heated  even  to  softening,  they 
do  not  become  vesicular.     They  are  triangular,  but  are  not 
accompanied  with  covers,  a  want  very  often  felt  in  the  labo- 
ratory.    They  are  usually  of  a  brown  colour,  are  harder  than 
English  crucibles,  scarcely  yielding  to  a  knife  or  to  glass; 
they  are  more  compact,  and  are  interspersed  with  black  par- 
ticles ;  the  fracture  is  sharper.     The  price  is  about  Id.  for 
the  nest  of  five  or  six  crucibles. 

644.  Cornish  crucibles.  Round  crucibles  of  different  sizes 
are  made  in  Cornwall,  for  the  use  of  the  assay  masters,  and 
are  plentiful  there,  but  not  common  in  London.     They  may 
be  bought  of  Mr  Beauchamp,  22,  Grafton-street,    Soho. 
They  are  equally  good  with  the  Hessian  crucibles.     They  re- 
sist a  very  high  temperature,  and  on  softening  do  not  be- 
come vesicular  and  frothy.    ,They  agree  with  the  Hessian 
crucibles  in  hardness,  fracture,  and  in  all  points  except  colour, 
being  white  or  nearly  so ;  covers  of  the  same  material  may 
be  obtained. 

645.  Wedgwood' s  crucibles  are  made  of  a  close  white  ware, 
and  hence,  though  thin,  it  is  difficult  to  dissolve  them,  and 
they  retain  fluxes  at  moderate  temperatures  longer  than  other 
crucibles.     They  are  round,  well  formed  and   finished,  and 
their  covers  fit  with  considerable  accuracy.     They  are  liable 
to  crack  when  heated,  or  if  this  be  prevented  by  care,  they 
frequently  do  so  in  cooling,  which  renders  it  necessary  to 
use  much  caution  during  change  of  temperature.    They 

2N 


298  CRUCIBLES — MOST  REFRACTORY. 

bear  a  moderately  high  heat,  surpassing  in  that  respect  the 
common  English  crucible,  but  not  equalling  the  Hessian  or 
Cornish. 

646.  Blue  pots  or  black-lead  crucibles  are  made  of  a  mix- 
ture of  coarse  plumbago  and  clay,  and  are  generally  of  large 
size,  being  intended   principally  for  use  in  the  arts.     They 
bear  a  higher   temperature  than  the  English  crucible,  are 
not  so  liable  to  crack  when  suddenly  heated  or  cooled,  and 
resist  the  action  of  fluxes  better  than  most  others  at  mode- 
rate furnace  temperatures ;  but  as  they  contain   abundance 
both  of  iron  and  charcoal,  they  cannot  be  used  in  experi- 
ments where  either  the  one  or  the  other  would  be  injurious. 
Covers  to  these  crucibles  of  the  same  material  may  be  ob- 
tained. 

647.  Attempts  have  been  made  to  improve  earthenware 
crucibles,  but  as  yet  none  equalling  the  Hessian  in  the  pow- 
er of  sustaining  a  high  temperature  unchanged  have  been 
produced  in  this  country  except  the  Cornish.     Those  made 
by  Marshall*  and  Ansteyf  are  said  to  approach  in  some 
properties  to  the  blue  pots.     They  are  made  of  Stourbridge 
clay  and  pulverized  coke  ;  Anstey's  are  not  baked   previous 
to  use.     These  vessels  bear  temperatures  equal  almost  to 
those  which  are  sustained  by  a  Cornish  or  Hessian  crucible, 
and  with  care  are  but  little  subject  to  crack  in  the  fire. 
They  are  principally  in  use  as  melting  pots. 

648.  Of  all  these  varieties  the  Hessian  and  Cornish  cruci- 
bles are  the  most  valuable  in  the  laboratory.     They  are  ge- 
nerally used  singly,  and  uncoated,  but  on  particular  occa- 
sions it  is  advantageous  to  place  one  in  another,  and  by  tak- 
ing two  successive  ones  from  a  nest,  a  double  crucible  may 
thus  be  obtained,  which  is  not  very  clumsy.    They  should 
not  be  put  simply  one  into  the  other  and  then  used,  but 
Stourbridge  clay  (1101),  mixed  with  water  into  a  smooth  and 
rather  soft  paste,  should  be  put  at  the  bottom  and  about  the 
inside  of  the  larger,  in  such  quantity  that,  on  introducing 
the  smaller,  and  applying  pressure,  it  may  come  in  contact 
with  the  clay  in  every  part,  the  excess  being  thrust  out  at 
the  edge  between  the  two  vessels.     It  requires  some  power 
to  force  in  the  smaller  crucible  and  displace  the  excess  of 

*  Trans.  Soc.  Arts.  xli.  52.  t  Ibid,  xliii.  32. 


CRUCIBLES OF  CHARCOAL— LINED.  299 

clay.  This  object  is  best  effected  by  placing  the  crucibles 
with  the  mouths  downward  on  a  table,  and  pressing  on  the 
bottom  of  the  larger,  whilst  a  little  twisting  or  lateral  motion 
is  given,  until  its  edge  is  also  in  contact,  or  nearly  so,  with 
the  table.  The  two  crucibles  being  thus  by  the  intervening 
clay  compacted  into  one,  must  be  put  into  a  warm  place  (605) 
and  left  for  some  days  to  dry.  They  must  not  be  used  in  a 
damp  state. 

649.  A  Wedgwood's  crucible  is  sometimes  advantageous- 
ly luted,  and  is  then  not  so  liable  to  crack  by  the  heat  as  if 
unprotected.     Or,  sometimes  one  may  be  placed  as  a  lining 
within   a  Cornish  crucible;  but  being  more  delicate,  less 
force  must  be  used  than  in  the  case  above  (648),  and  the 
paste  of  Stourbridge  clay  is  to  be  made  somewhat  thinner. 

650.  Charcoal  crucibles  are  very  convenient  for  certain 
operations  of  reduction.     Klaproth  recommends  that  they  be 
formed  by  making  a  cavity  in  a  piece  of  well  burned  charcoal, 
answering  to  the  size  of  the  substance  to  be  operated  with 
with  a  charcoal  stopper  to  close  the  mouth.     The  charcoal 
vessel  is  then  to  be  fitted  into  a  common  clay  crucible,  which 
last  is  to  be  well  covered  and  luted. 

651.  Stoppers  or  covers  may  be  made  out  of  solid  char- 
coal, and  as  that  of  alder  wood  does  not  crack  or  fly  to 
pieces  when  heated,  it  is  best  adapted  for  the  purpose ;  but 
it  is  requisite  previously  to  heat  the  charcoal  to  a  high  de- 
gree in  consequence  of  the  contraction  which  that  substance 
undergoes,  and  which  appears  to  be  proportionate  to  the 
temperature  it  is  submitted  to.     Charcoal  made  as  it  usually 
is,  by  mere  ignition,  when  fitted  and  then  subjected  to  high 
heat,  will   be  considerably  deranged,  from  the  contraction 
occasioned   by  a  greater   temperature ;  but   if  previously 
strongly  ignited  this  derangement  is  avoided. 

652.  For  a  similar  purpose  it  is  often  advantageous  to 
line  crucibles  with  charcoal.     The  charcoal  should  be  pul- 
verized, and  the  more  compact  and  close  the  lining  is  re- 
quired, the  finer  should  be  the  powder ;  for  in  consequence 
of  the  porosity  of  charcoal  its  powder  lies  in  a  much  smaller 
space  than  the  solid  or  coarsely  pounded  substance.     It  is  to 
be  mixed  with  weak  gum  water,  not  putting  so  much  as  to 


300          CRUCIBLES — PLATINUM CAPSULES. 

make  it  adhere,  but  forming  with  it  a  moist  powder ;  the 
crucible  is  to  be  lined  with  a  coat  of  this,  from  the  fourth  to 
the  half  of  an  inch  or  more  in  thickness.  The  cavity  is  to 
be  finished  by  a  smooth  mould,  or  rather  core,  as  the  end 
of  a  pestle  or  a  properly  formed  piece  of  wood ;  and  hav- 
ing pressed  the  lining  as  hard  as  possible  with  this,  it  is  to  be 
withdrawn  carefully,  first  giving  a  little  rotatory  or  lateral 
motion,  so  as  to  set  it  free  from  the  lining  without  causing  de- 
rangement. The  crucible  is  then  to  be  set  in  a  warm  place  to 
dry  (605). 

653.  Amongst  metallic  crucibles,  those  formed  of  platinum 
are  most  generally  useful :  they  should  be  accompanied  by 
covers  of  the  same  metal.     They  are  usually  made  with  a 
flat  bottom  meeting  the  sides  at  a  sharp  angle,  and  then 
have  the  advantage  of  standing  steadily;  but  they  are  pe- 
culiarly liable  to  injury  at  this  angle,  not  only  because  they 
are  often  thinner  there  than  elsewhere,  but  from  blows  upon 
the  outside,  and  from  endeavours  by  means  of  hard  instru- 
ments to  loosen  their  contents.     The  substance  adhering  to 
it  should,  on  account  of  the  value  of  a  platinum  crucible,  be 
loosened  as  much  as  possible  by  solution,  and  afterwards 
removed  by  smooth  or  blunt  bodies,  as  glass  rods,  or  spatu- 
las.    By  making  the  crucible  with  a  round  bottom,  or  egg- 
shaped,  the  disadvantages  attending  the  angle  are  avoided, 
but  the  inconvenience  of  not  standing  by  itself  is  incurred. 
It  is  however,  when  hot,  easily  supported  in  the  sand-bath, 
and  when  cold,  either  there  or  on  the  top  of  a  test-glass 
(505).     The  two  forms  are  equally  well  supported  in  the 
furnace. 

654.  Platinum  capsules  have  been  before  referred  to  (371). 
They  are  useful  in  heating  bodies  either  in  the  furnace  or 
by  the  spirit-lamp,  and  often  supply  the  place  of  crucibles. 
When  a  cover  is  wanted,  one  will  serve  that  purpose  to 
another,  or  even  to  the  platinum  crucible  itself;  and  the 
crucible  cover  may  be  useful  in  conjunction  with  the  cap- 
sules. 

655.  A  platinum  crucible  may  often  be  inserted  with  ad- 
vantage into  a  Cornish  one,  but  it  is  better  not  to  introduce 
any  intervening  substance.     The  metal  crucible  is  thus  pro- 


CRUCIBLES SILVER — GOLD.  301 

tected  from  impurities  in  the  fuel,  and  from  the  forcible  ac- 
tion of  the  tongs  in  moving  it  into  and  out  of  the  furnace. 

656.  A  silver  crucible  and  cover  is  a  useful  vessel ;  it 
may  in  many  cases  be  used  instead  of  the  platinum  crucible 
and  being  of  a  cheaper  metal,  may  be  formed  of  larger  size. 
It  is  of  great  service  in  the  evaporation  of  mineral  waters, 
and  various  solutions.     It  should  be  of  pure  silver.     It  should 
be  carefully  attended  to  when  heated,  because  silver  fuses 
at  a  full  red,  or  rather  yellow  heat ;  and  because  in  a  fur- 
nace, amongst  the  fuel,  there  are  frequent  air-ways  and  cur- 
rents of  small  extent,  by  which  one  part  of  a  crucible  is  ren- 
dered much  hotter  than  another.     It  should  be  understood, 
that  as  the  heat  approaches  the  fusing  point,  there  are  cer- 
tain temperatures  at  which  the  crucible  will  appear  quite 
whole  and  sound,  even  when  it  is  so  friable  and  brittle,  that 
if  held  at  one  edge,  its  weight  is  sufficient  to  break  a  piece 
out.     Hence  it  is  best  never  to  trust  it  in  any  other  than  the 
crucible  furnace  (158),  where  it  can  be  most  conveniently 
watched,  and  where  the  heat  is  not  so  liable  to  rise  unob- 
served as  in  a  close  furnace.     It  may  sometimes  be  put  with 
advantage  into  a  Cornish  or  a  Wedgwood  crucible. 

657.  Klaproth,  who  has  the  merit  of  first  applying  fixed 
alkalies  to  the  analysis  of  minerals  by  heat,  found  silver  and 
platinum  crucibles  so  much  acted  upon  by  them,  as  to  be 
induced  to  make,  and  earnestly  to  recommend,  a  vessel  of 
pure  gold  for  this  purpose.     Such  a  crucible  is  by  no  means 
liable  to  the  same  kind  or  extent  of  injury  as  the  former,  but 
is  very  fusible  in  the  fire. 

658.  No  other  furnace  fuel  than  charcoal  should  ever  be 
used  to  metallic  crucibles.     The  sulphureous  fumes  which 
rise  from  coke  and  coal  injure  them;  and  iron  and  other 
substances  present  do  not  merely  form  slags,  which  adhere 
to  the  vessels  and  soil  them,  but  actually  corrode  and  destroy 
them. 

659.  These  crucibles  gradually  deteriorate  and  become 
injured  by  successive  operations  :  platinum  frequently  rises 
into  blisters,  which  are  exceedingly  inconvenient,  not  merely 
as  weakening  the  vessel,  but  as  forming  cavities;  portions  of 
the  matter  fused  in  the  crucible  are  retained  in  these  cavi- 


302  CRUCIBLES — IRON — SUBSTITUTES. 

ties,  and  being  very  difficult  of  removal,  often  remain  and 
cause  injury  by  contaminating  the  future  operations.  The 
surface  of  the  metal,  also,  gradually  becomes  roughened, 
and  the  whole  is  rendered  more  or  less  brittle.  The  purest 
platinum  undergoes  these  changes  in  time,  partly  perhaps 
from  the  fumes  of  the  fuel  in  the  furnaces,  or  the  slight,  but 
successive  action  of  the  substances  heated  in  it.  Silver  cru- 
cibles change  much  more  rapidly,  and  after  some  time  ac- 
quire a  crystalline  structure  and  become  very  brittle. 

660.  An  iron  crucible  is  occasionally  required ;  though 
but  seldom  for  experiments  of  ignition.     On  the   whole, 
though  a  more  fusible  material,  it  is  better  of  cast  than  of 
wrought  metal. 

661.  When,  in  the  absence  of  crucibles,  an  extemporary 
vessel  of  this  kind  is  required,  it  may  either  be  a  tobacco- 
pipe,  or  a  piece  of  green  glass  tube  luted,  or  a  china  cup  or 
its  fragments. 

662.  In  the  appropriation  of  metallic  crucibles  to  particu- 
lar uses,  it  is  tq  be  observed  that  fusible  metals,  or  com- 
pounds of  metals  likely  to  be  reduced,  must  never  be  heated 
in  vessels  of  silver,  gold,  or  platinum  ;  otherwise  alloys  will 
be  formed,  the  crucible  destroyed,  and  its  contents  lost. 
Even  several  chlorides  which  are  unchanged  in  and  cause 
no  injury  to  glass,  will,  when  heated  in  platinum  under  or- 
dinary circumstances,  injure  it.     This  is  the  case  with  chlo- 
ride of  lead,  which  being  partially  reduced,  the  crucible  be- 
comes lined  with  an  alloy  of  lead,  and  seriously  injured.     It 
is  the  same  with  oxide  of  lead  and  many  compounds  con- 
taining that  metal,  such  as  flint  glass.     These   crucibles 
should  be  used,  therefore,  only  with  infusible  substances  in 
mass  or  powder,  or  with  such  fluids  as  will  not  act  upon  them. 
In  analyses  the  chemist  is  frequently  obliged  to  heat  alkalies 
in  them,  because  no  other  vessels  resist  their  action  so  well. 
Caustic  alkalies  act  at  a  high  temperature  upon  both  plati- 
num and  silver,  though  not  rapidly  :  the  action  is  much  in- 
creased by  free  access  of  air,  and  seems  to  be  dependant  in 
part  upon  the  formation  of  a  portion  of  the  peroxide  of  the 
alkaline  metal,  oxygen  being  afterwards  transferred  from  it 
to  the  crucible.     The  carbonated  alkalies  do  not  act  upon 


CRUCIBLES APPROPRIATED.  303 

either,  but  they  cannot  be  fused  safely  in  silver,  from  the 
high  temperature  they  require.  When  charcoal  is  mixed 
with  the  carbonated  alkalies,  action  takes  place  slowly  on 
platinum,  perhaps  in  consequence  of  the  formation  of  a  por- 
tion of  potassium. 

663.  When   the  characters  exhibited  by  earthy  bodies, 
upon  being  heated,  are  to  be  ascertained,  the  earths  must 
not,  as  Klaproth  has  shown,  be  put  into  earthen  crucibles*. 
Vitrification  frequently  takes  place,  in  consequence  of  an 
action  which  occurs  at  the  surface  of  contact,  when  it  would 
not  happen  in  crucibles  of  charcoal  or  metal. 

664.  Earthen  crucibles  are  best  adapted  for  the  retention 
of  metals  at  high  temperatures,  and  consequently  for  all  ex- 
perimental attempts  to  reduce  them ;  but  there  are  certain 
liabilities  to  which  they  are  subject,  of  which  the  student 
must  be  aware.     The  action  of  fluxes  upon  them  has  been 
already  noticed  (642),  and  it  is  such  that  they  will  not  stand 
in  the  fire  beyond  a  certain  time,  proportionate  to  the  tem- 
perature and  dissolving  power  of  the  flux.     They  also  occa- 
sionally yield  substances  to  the  bodies  heated  in  them  ;  thus 
platinum  heated  highly  with  charcoal  in  an  earthen  cruci- 
ble, will  be  found  to  have  combined  with  silicon,  if  at  least 
the  temperature  has  been  carried  up  to  the  fusing  point ; 
and  either  wrought  or  cast-iron,  in  like  manner  heated  in- 
tensely in  an  earthen  crucible,  will  be   found  to  have  ac- 
quired silicon,  and  perhaps  aluminum. 

665.  Finally  with  reference  to  the  selection  of  these  ves- 
sels, it  is  generally  best  to  reject  an  earthen  crucible  that 
has  once  been  used,  except  it  be  large,  in  good  condition, 
and  required  for  a  repetition  of  a  former  process.     For  the 
numerous  small  and  varied  experiments  made  in  the  labora- 
tory, it  is  always  advisable  to  commence  with  clean  vessels, 
and  to  throw  them  away  when  done  with,  lest  any  impurity 
should   be   communicated   to  an   important   result.      The 
cheapness  of  crucibles  removes  the  charge  of  extravagance 
from  such  a  practice  ;  one   failure  in  an  experiment  is  of 
more  consequence  than  the  second  use  of  several  earthen 
crucibles. 

*  Klaproth's  Analytical  Etsays,  vol.  ii.,  pp.  35, 36. 


304  CRUCIBLES  HEATED — JACKETS. 

666.  The  apparatus  for  the  application  of  heat  requisite 
for  crucible  operations,  as  lamps,  furnaces,  &c.,  has  been 
already  described  (Sect,  iv.);  so  that  now  there  remains  but 
to  notice  such  circumstances  as  peculiarly  relate  to  their  use 
with  crucibles.     The  small  and  the  large  spirit  lamps  (199, 
205,  228)  answer  well  for  platinum  crucibles  and  capsules, 
when  the  heat  they  communicate  is  sufficient ;  for  no  fumes 
arise  which  can  occasion  injury  to  the  metal.     If  the  tran- 
quil flame  of  the  lamp  be  hardly  sufficient,  the  broken  flame 
obtained  by  the  blow-pipe  before  described  (233,  245)  may 

be  used.  The  crucible  may  be  con- 
iveniently  supported  by  apiece  of  iron- 
wire,  bent  so  as  to  form  a  ring  at  each 
end,  one  about  two-thirds  of  an  inch  and  the  other  one  and 
a  quarter  inch  in  diameter,  separated  by  a  straight  line 
seven  inches  in  length ;  the  wire  should  be  pushed,  before 
being  bent,  through  a  couple  of  phial  corks,  which,  when 
brought  to  the  middle  of  the  straight  part,  serve  as  a  handle, 
and  prevent  the  hot  metal  from  burning  the  hand. 

667.  The  heating    power  of  the  tranquil  flame  is  much 

economised,  and  the  temperature  of 
the  crucible  increased,  by  using  a 
jacket  like  that  represented  partly 
in  section  and  partly  in  perspective 
in  the  wood  cut.  It  is  to  be  made 
of  sheet-copper  or  iron,  open  at  the 
top  and  bottom,  and  within  it,  three 
projecting  slips  of  iron-plate  are  to 
be  fixed  by  rivets,  intended  to  support  the  crucible  on  their 
edges.  This  jacket  is  to  be  sustained  on  the  ring  of  a  re- 
tort stand,  the  crucible  placed  within  it,  and  the  spirit-lamp 
beneath.  The  supporting  slips  should  be  of  such  dimensions 
as  to  leave  a  space  of  about  the  third  of  an  inch  between  the 
crucible  and  the  jacket,  in  which  the  flame  moving  tranquilly, 
wraps  itself  around  the  crucible,  and  as  no  flickering  motion 
takes  place,  every  portion  is  thus  effectually  applied.  The 
loss  of  heat  from  the  crucible  by  radiation  and  contact  of  cold 
air,  is  very  much  diminished,  and  this  is  still  further  lessened 


CRUCIBLES JACKETS FURNACE.  305 

when  the  cover  is  on  the  crucible.  A  very  important  differ- 
ence in  the  temperature  of  the  contents  of  a  metallic  cruci- 
ble, depends  upon  the  circumstances  of  the  cover  being  on 
or  off.  The  spirit-lamp  used  to  heat  the  crucible  must  bear 
some  proportion  to  the  size  of  the  vessel,  and  the  quantity 
of  its  contents.  The  two  mentioned  (199,205)  are  suffi- 
cient for  most  purposes  when  platinum  crucibles  are  used. 

668.  The  jacket  is  also  of  highly  advantageous  applica- 
tion in  the  use  of  an  oil  (212,  213)  or  gas-lamp  (215),  and  is 
often  economical  in  distillations,  evaporations,  &c.     A  se- 
cond, on  a  larger  scale,  must  then  be  used  for  the  larger 
sized  retorts,  and  it  should  not  have  supporting  slips  within, 
but  the  jacket  and  retort  should  be  sustained  independently 
of  each  other  ;  for  otherwise  the  edges,  from  the  rapid  man- 
ner in  which  they  become  heated,  would  often  occasion  the 
fracture  of  the  glass. 

669.  In  considering  the  relations  of  furnaces  to  the  cruci- 
bles that  may  be  heated  in  them,  it  is  hardly  necessary  to 
notice  the  table-furnace  (169).     Any  crucible  less  than  six 
inches  in  height,  and  four  inches  in  diameter  at  the  top,  may 
be  heated  to  full  redness  in  it.     It  may  be  set  on  the  fuel  and 
raised  now  and  then  when  needful  by  tongs,  or  be  put  upon 
a  square  piece  of  soft  brick  about  an  inch  thick,  placed  upon 
the  bars.     As  before  mentioned,  coke  should  be  the  fuel 
used  (192),  and  a  cover  (of  common  English  ware  or  black 
lead)  should  be  applied,  when  the  highest  heat  is  required ; 
the  furnace-door  should  be  shut,  the  ash-door  open,  plenty 
of  fuel  around  and  upon  the  crucible,  and  all  extra  flues  com- 
municating with  the  chimney  closed. 

670.  When  a  crucible  is  to  be  heated  in  a  crucible-fur- 
nace (158),  the  grate  should  be  placed  in  it  not  less  than 
half  way  from  the  top  (160).     The  furnace  should   be  of 
such  a  size  as  to  allow  at  least  two  inches  of  space  for  fuel 
all  round  the  crucible,  when  the  latter  is  two  inches  in  di- 
ameter or  less,  and  somewhat  more  if  it  be  so  much  as  three 
inches  in  diameter  :  this  will  permit  the  supply  of  fuel  in 
sufficient  quantity  to  produce  a  strong  heat.     When  a  fire 
is  to  be  lighted  in  the  furnace,  a  few  pieces  of  charcoal  may 

2O 


306  ARRANGEMENT FUEL. 

be  put  into  a  common  fire,  and  when  ignited  placed  in  the 
crucible  furnace,  and  being  afterwards  covered  by  charcoal 
the  combustion  will  soon  become  sufficiently  vivid.  If  the 
crucible  to  be  heated  be  of  platinum,  it  may  be  placed  on 
the  fuel,  the  cover  put  on,  and  charcoal  added  to  the  sides. 
Unless  a  strong  heat  be  required,  it  will  not  be  necessary  to 
place  fuel  over  the  crucible,  but  if  there  be  occasion  for  a 
high  temperature,  the  fuel  is  to  be  piled  up,  and  even  the 
flue  (165)  used.  As  the  fuel  sinks,  it  must  be  re-adjusted 
with  the  tongs,  the  crucible  raised,  and,  if  the  heat  has  not 
been  continued  long  enough,  fresh  fuel  is  to  be  added.  The 
crucible  should  never  be  allowed  to  sink  to  the  grate.  If  it 
contains  a  soft  or  pasty  substance,  it  should  be  carefully 
watched,  to  prevent  its  position  from  being  deranged,  or  the 
cover  displaced.  It  will  acquire  the  highest  temperature 
when  about  an  inch  and  a  quarter  from  the  grate,  equally 
distant  from  the  sides  of  the  furnace,  covered  with  about  an 
inch  of  the  fuel,  and  with  the  temporary  flue  over  it. 

671.-  If  the  heat  is  to  be  continued  longer  than  during  the 
combustion  of  one  charge  of  fuel,  a  stand  should  be  used  for 
the  crucible.  This  may  be  a  small  crucible  about  one  inch 
and  a  half  high,  turned  upside  down,  with  a  little  sand  or 
clay  between  it  and  the  experimental  crucible ;  or  an  Eng- 
lish cylindrical  crucible  with  the  mouth  upwards,  either 
empty  or  filled  with  sand ;  or  a  small  round  pillar  of  soft 
brick  (1354).  It  should  be  put  into  its  place,  the  furnace 
lighted,  the  crucible  arranged,  the  fuel  added,  and  the  heat 
raised.  The  fuel  should  not  be  suffered  to  burn  down  very 
low,  nor  should  much  be  added  at  once  ;  but  the  addition 
should  be  gradual  and  continual,  that  the  crucible  may  nev- 
er be  left  exposed  to  the  air  if  the  experiment  has  in  the 
first  instance  required  it  to  be  covered.  Cold  fuel  suddenly 
diminishes  the  temperature  of  that  part  of  the  fire  with  which 
it  comes  in  contact,  which  if  it  occur  where  the  crucible  it- 
self is  situatejd,  causes  injurious  variations  in  its  temperature. 

672.  The  temperature  of  a  furnace  should  never  be  al- 
lowed to  rise  and  fall  suddenly  and  irregularly,  whilst  an 
operation  is  going  on.  Such  changes  are  liable  to  affect 


ARRANGEMENT FUEL.  307 

the  temperature  of  the  crucible,  and  even  to  cause  its  frac- 
ture. 

673.  The  utmost  heat  that  can  be  given  to  a  crucible  is 
to  be  attained  in  the  laboratory  by  such  a  blast-furnace  as 
has  been  already  described  (184);  the  fuel  being  coke  or 
coke  and  charcoal,  (187,  191,  193.)     When  of  the  dimen- 
sions specified,  it  will  heat  a  crucible  three  inches  and  a  half 
high,  and  two  inches  and  three-quarters  in  its  upper  diame- 
ter, very  highly  ;  and  one  not  more  than  one  inch  and  three- 
quarters  diameter  at  the  top,  intensely.     To  acquire  the 
most  powerful  heat,  the  crucible  should  be  raised  about  one 
and  a  half  or  two  inches  from  the  grate,  and  covered  with  at 
least  the  same  depth  of  fuel.     Hence  arises  a  necessity  for 
supports  and  covers,  capable  of  resisting  intense  tempera- 
tures.   The  best  supports  would  be  crucibles  made  of  the 
Cornish  or  Hessian  clay,  of  a  cylindrical  form,  from  one  and 
a  half  to  two  inches  in  height,  and  from  half  an  inch  to  an 
inch  internal  diameter ;  the  closed  end  being  put  upon  the 
grate,  and  the  bottom  of  the  crucible  on  or  into  the  aperture 
above,  where  it  would  be  steadily  retained.     But  in  the  ab- 
sence of  such  supports,  recourse  must  be  had  to  Cornish  or 
Hessian  crucibles,  and  one  being  selected  with  a  flat  bottom 
it  must  be  placed  upside  down,  with  the  mouth  upon  the 
grate.     From  the  irregular  form  of  the  bottoms  of  these 
crucibles,  and  the  necessity  of  choosing  them  as  narrow  as 
possible,  that  the  fuel  may  be  close  to  all  parts  of  the  cru- 
cible to  be  heated,  the  latter  is  necessarily,  when  simply 
placed  upon  the  stand,  very  tottering ;  it  is,  therefore,  gen- 
erally advisable  to  lute  the  crucible  and  stand  together  with 
a  little  Stourbridge  clay,  a  small  portion  being  put  between 
the  two  surfaces,  and  more  at  the  sides,  so  as  in  fact  to  make 
the  two  vessels  into  one,  their  bases  being  attached  together. 
Such  luting  must  be  well  dried  for  a  day  or  two  before  it  is 
placed  in  the  furnace  (1084). 

674.  With  respect  to  covers,  the  arrangement  is  more  dif- 
ficult, in  consequence  of  the  absence  of  those  necessary  ac- 
companiments to  Hessian  crucibles,  and  the  uncertainty  at- 
tending the  supply  of  them  with  Cornish  crucibles.     Sup- 
pose that  iron  or  steel  is  to  be  heated  without  contact  of 


308  CRUCIBLES — COVERED LUTED. 

carbonaceous  or  extraneous  substances  of  any  kind.  A  com- 
mon English  cover  will  not  answer  the  purpose,  because  it 
will  melt  and  run  into  the  crucible.  A  larger  crucible  of 
the  same  kind  may  be  turned  over  it,  and  luted  at  the  edges; 
but  this  inconveniently  increases  the  size  of  the  mass  to  be 
heated,  which,  when  the  highest  temperature  is  required, 
should  be  as  small  as  possible.  A  smaller  crucible  of  the 
same  kind  may  'be  inverted  and  put  inside  the  other,  and  the 
interval  filled  by  a  luting  of  Stourbridge  clay ;  but  the  heat 
contracts  the  lute,  the  fissures  of  which  may  receive  particles 
of  fuel  and  slag.  This  is  the  more  probable,  because  in  all 
cases  of  a  blast  in  the  furnace  from  below  upwards,  there  is 
an  eddy  in  the  stream  of  air  above  the  crucible  which  stands 
as  a  fixed  obstacle  in  the  current,  and  which  causes  the  re- 
turn and  accumulation  of  numerous  small  particles  upon  the 
top. 

675.  The  method  that  has  been  found  to  answer  best  is  to 
beat  up  some  Stourbridge  clay  with  water  into  a  stiff  paste, 
to  make  it  into  a  cake  the  fourth  of  an  inch  thick,  to  put  it 
over  the  top  of  the  crucible,  to  press  it  down  with  a  common 
English  cover  of  proper  size,  so  as  to  force  a.  cake  of  the 
damp  clay  into  the  crucible,  and  cut  off  the  excess  by  its 
edge,  and  then  to  finish  by  luting  the  edge  of  the  cover  and 
the  side  of  the  crucible  together.     This  is  to  be  done  before 
the  crucible  is  luted  upon  its  stand,  and  the  whole  is  to  be 
well  dried  previous  to  being  used.     When  heat  is  applied, 
the  internal  cover  of  the  lute  becomes  baked,  and  though  it 
diminishes  in  size,  yet  from  the  form  of  the  crucible,  it  sel- 
dom sinks  down  to  the  charge;  and  if  the  English  external 
cover  soften  and  fuse,  it  is  still  supported  on  the  former,  and 
generally  serves  to  keep  out  impurities. 

676.  When  the  crucible  is  of  charcoal,  or  is  lined  with 
charcoal  and  consequently  has  a  charcoal  stopper  inside 
(651),  the  common  cover  may  be  put  directly  over  it  and  lu- 
ted; and  even  in  plain  crucibles,  when  charcoal  is  not  inju- 
rious, an  internal  cover  of  it,  formed  out  of  one  or  several 
pieces,  may  be  used  instead  of  the  plate  of  lute,  and  the 
ordinary  cover  then  put  over  it. 

677.  The(  furnace  being  clean  and  in  orBer,  and  the  cru- 


FIRE  LIGHTED SUSTAINED.  309 

cible  with  its  luted  cover  and  stand  dry,  the  latter  is  to  be 
placed  steadily  on  the  grate  of  the  furnace;  a  few  pieces  of 
lighted  charcoal  are  to  be  dropped  in  and  covered  by  cold 
charcoal  to  the  depth  of  two  or  three  inches,  and  the  whole 
left  until  the  combustion  has  spread  amongst  the  fuel;  the 
air  will  find  sufficient  access  through  the  aperture  beneath. 
When  the  crucible  becomes  warm,  coke  is  to  be  added  so  as 
to  cover  it,  and  the  temporary  flue  (165)  is  to  be  adjusted,  to 
assist  the  draught.  When  the  fuel  is  nearly  red-hot  an  inch 
or  two  below  the  surface,  more  coke  is  to  be  added  until  it 
rises  about  two  or  three  inches  above  the  crucible,  the  flue 
is  then  to  be  replaced,  and  the  combustion  to  proceed  until 
the  crucible  itself  is  red  hot.  This  will  occupy  perhaps  an 
hour,  and  require  attention  only  at  the  short  intervals  when 
coke  is  to  be  added.  The  course  described  is  adapted  to  the 
object  of  raising  the  heat  steadily  and  gradually  to  redness; 
it  may  be  well  to  explain,  that  the  coke  should  not  be  put  on 
until  the  crucible  has  been  somewhat  warmed  by  the  char- 
coal, to  prevent  the  deposition  upon  it  of  the  water  driven 
from  the  fuel.  Having  attained  a  red  heat,  the  flue  must  be 
removed,  the  bellows  applied  (185,188),  slowly  at  firsthand 
more  powerfully  as  the  heat  rises,  until  the  highest  point 
required,  or  that  is  possible,  be  attained. 

678.  It  is  very  desirable  that  the  heat  should  be  raised 
regularly,  and  sustained  steadily.  For  this  reason  the  blast 
should  not  be  variable,  but  uniform.  As  the  combustion 
goes  on  the  fuel  will  generally  fall  freely,  but  it  should  be 
touched  now  and  then  by  the  tongs  or  an  iron  rod,  in  order 
that,  if  hollow  places  should  occur,  they  may  be  filled  up 
without  delay.  The  fuel  should  never  be  allowed  to  burn 
away  very  low  and  then  a  large  quantity  of  cold  fuel  piled 
on;  but  it  should  be  supplied  at  small  intervals,  the  top  of 
the  crucible  never  being  left  uncovered,  except  pur- 
posely, to  observe  that  it  has  not  melted  down.  Cold  fuel 
should  not  be  allowed  to  come  in  contact  with  it;  even  bright 
red-hot  fuel  will  cool  a  white-hot  crucible.  All  these  pre- 
cautions in  heating  the  crucible  are  necessary  to  insure  the 
fullest  advantage,  that  may  be  attained  in  the  short  time 
which  an  operation  in  this  furnace  generally  requires. 


310  CRUCIBLE  IN  BLAST  FURNACE DEFENDED. 

When  the  crucible  is  large,  or  double,  or  is  lined  with 
charcoal,  or  contains  a  considerable  charge,  it  is  some  time 
before  it  acquires  a  temperature  approaching  to  that  of  the 
fuel  on  the  outside;  and  if  the  heat  has  been  raised  in  an 
intermitting  manner,  or  if  the  fuel,  after  being  allowed  to 
burn  low,  has  been  replenished  by  cold  portions,  the  furnace 
may  have  appeared  very  hot  occasionally,  and  yet  no  pro- 
portionate effect  be  obtained  within  the  crucible. 

679.  When  very  high  temperatures  are  required,  as  in  the 
fusion  of  platinum  or  rhodium,  the  crucibles  become  so  soft  as 
to  sink  and  fold  like  leather,  and  the  results  are  often  lost. 
This  is  sometimes  due  in  part  to  the  pressure  of  the  fuel 
upon  the  crucible,  and  may  be  prevented  by  hanging  a 
shelter  over  it.     A  long  narrow  English  pot,  having  a  mouth 
a  little  larger  than  the  crucible  to  be  heated,  is  to  be  select- 
ed, and  a  hole  made  through  its  bottom;  by  passing  an  iron 
rod  with  a  hooked  end  through  this  hole,  the  pot  may  be 
suspended  in   an  inverted  position  over  the  crucible  and 
within  half  an  inch  of  it,  thus  preventing  the  contact  of  the 
fuel  with  its  top.  Care  will  be  requisite  that  the  expansion  of 
the 'rod   and   vessel,   as  the  heat  rises,   should  not  cause 
the  latter  to  press  upon  the  crucible.     A  great  depth  of  fuel 
is,  on  these  occasions,  to  be  preserved  in  the  furnace  round 
the  shelter,  to  compensate  as  much  as  possible  for  its  effect 
in  diminishing  the  temperature;  and  this,  with  a  little  more 
than  common  application  of  the  bellows,  is  always  suffi- 
cient for  the    purpose.      In  this  way  many  crucibles    and 
their  contents  have  been  saved,  which,  from  the  average  of 
experiments  without  the  shelter,  there  is  reason  to  believe 
would  have  been  lost. 

680.  When  an  operation  in  this  furnace  is  considered  as 
concluded,  it  is  best  to  withdraw  the  bellows,  and  to  let  the 
temperature  sink  a  little  before  the  crucible  is  disturbed, 
otherwise  the  heat  will  be  unbearable,  and  the  vessel,  from 
its  softness,  will  be  liable  to  injury.     If  allowed  to  cool  en- 
tirely in  the  furnace  no  harm  results,  and  occasionally  much 
advantage. 

681.  Whether  this  or  any  other  furnace  is  used,  care  is 


CRUCIBLES GENERAL  REMARKS. 

necessary  in  moving  the  crucibles  with  the  tongs  when  in 
the  fire,  or  in  putting  them  in  and  taking  them  out.  If  heav- 
ily laden,  and  nipped  by  the  tongs  at  one  edge,  they  should 
not  be  held  too  upright,  lest  the  weight  break  them.  Atten- 
tion should  also  be  paid  that  no  impurity  be  communicated 
to  their  contents,  from  the  tongs  or  from  the  fuel,  by  awk- 
ward management.  If  the  charge  is  fluid,  as  in  analytical 
processes,  the  tongs  should  never  touch  any  part  of  the  inner 
surface  where  the  fused  matter  has  adhered,  lest  they  not 
only  convey  impurity,  but  remove  a  part  of  the  charge. 

682.  The  following  general  remarks  upon  the  objects  of 
these  operations  may  be  useful.     If  the  object  be  the  igni- 
tion of  a  mixture  for  analysis,  or  the  desiccation  of  analytical 
products,  then  a  platinum  crucible  with  its  cover,  raised  either 
by  the  lamp  or  the  charcoal  furnace  to  a  moderate  red  heat, 
is  sufficient.     When  the  substance  is  to  be  weighed,  or  the 
loss  of  weight  ascertained,  the  crucible  is  first  to  be  counter- 
poised, then  weighed  with  the  substance  in  it,  afterwards 
heated  and  weighed  again  to  ascertain  if  there  be  loss.     The 
remaining  substance  is  then  to  be  removed,  and  the  crucible 
weighed  for  the  last  time,  to  see  that  the  counterpoise  con- 
tinues correct.     Or  if  it  be  a  substance  to  be  dried,  as  silica, 
it  is  first  to  be  weighed,  then  heated  carefully  and  weighed 
with  the  crucible  after  it  has  been  heated ;  the  substance  is 
then  to  be  removed,  the  crucible  wiped,  and  the  diminution 
of  weight  ascertained.     In    that  way  the    quantity  of  dry 
matter  it  contained  may  be  estimated  better  than  by  trans- 
ferring the  substance  itself  to  the  pan  and  weighing  it,  or  if 
the  latter  be  done,  the  weight  may  be  verified  by  the  former 
method  :  for  it  is  easier  to  remove  and  clean  all  the  substance 
out  of  the  crucible,  than  to  putitatf  into  the  balance  pan. 
If  a  substance  to  be  fused  or  dried  decrepitate  by  heat,  it 
should  first  be  pulverized  (315),  or  in  less  precise  cases  the 
crucible  should  be  covered.     If  the  object  be  to  observe  the 
changes  that  may  take  place  in  bodies  by  heat,  attention 
must  be  paid  to  the  precaution  pointed  out  by  Klaproth 
(663)  and  others,  as  to  the  mutual  action  of  the  crucible  and 
the  substance. 

683.  When  the  end  to  be  obtained  is  the  mutual  action  of 


312  CRUCIBLES FLUXES  PREPARED. 

bodies,  then  the  crucible,  being  charged,  is  to  be  heated 
gradually,  fluxes  being  used  as  seldom  as  possible ;  for  al- 
though they  are  very  advantageous  in  cleansing  the  reduced 
metal,  and  assisting  its  separation  from  embarrassing  impu- 
rities, they  corrode  and  weaken  the  crucible,  as  before  men- 
tioned (642).  In  making  alloys,  the  metals  are  to  be  well 
agitated  together  ;  for  in  some  cases,  even  when  apparently 
miscible  and  well  mixed,  there  is  as  Mr  Hatchet  has  shown, 
a  remarkable  tendency  to  separation*.  In  the  preparation 
of  alloys,  and  the  fusion  of  some  metals,  it  is  advantageous 
to  cover  the  surface  of  the  metal  with  pieces  of  charcoal,  to 
prevent  oxidation.  In  these  cases  a  loose  cover  should  be 
put  on  after  the  charcoal,  to  hinder  the  access  of  air,  and 
prevent  combustion  as  much  as  possible. 

684.  When,  in  an  analytical  process,  potash  is  to  be  used 
which  alkali  may  be  added  as  carbonate,  then  the  bicarbo- 
nate is,  very  serviceable,    for  it  will  fuse  down    without 
ebullition,  an  effect  which  always  takes  place  if  the  carbo- 
nate is  used,  or  even  pure  potash,  and  is  often  injurious. 

685.  Fluxes  are  very    frequently    required    in  cases  of 
chemical  actions  amongst  metallic  compounds  at  high  tem- 
peratures, and  often  cannot  be  dispensed  with.     Their  use 
is  to  protect  the  substance  from  the  air;  to  dissolve  impuri- 
ties which  would  otherwise  be  infusible;  and  to  convey  ac- 
tive agents,  as  charcoal  and  reducing  matter,  into  contact 
with  the  substance-  operated  upon. 

686.  White  flux  is  made  by  deflagrating  a  mixture  of 
equal  parts  of  nitre  and  cream  of  tartar  in  a  large  earthen 
crucible,  heated  red-hot  at  the  bottom.     The  mixture  should 
be  introduced  in  successive  small  quantities,  the  combustion 
of  one  portion  being  allowed  to  arrive  nearly  to  a  termina- 
tion before  another  is  thrown  in,  or  the  substance  will  be 
blown  out  of  the  crucible.     That  part  of  the  flux  which  has 
been  in  contact  with  the  sides  of  the  crucible,  when  remov- 
ed from  it,  should  be  separated  from  the  rest,  and  preserved 
apart ;  a  little  earthy  matter  being  usually  derived  from  the 

*  Philosophical  Transactions,  1803. 


WHITE    AND    BLACK    FLUX CRUDE    TARTAR.  313 

vessel,  which,  though  ordinarily  of  no  importance,  may 
be  of  consequence  in  delicate  experiments.  The  flux 
should  be  retained  in  a  closed  jar  or  bottle.  It  consists  al- 
most entirely  of  carbonate  of  potash,  the  nitric  acid  of  the 
nitre  and  the  combustible  tartaric  acid  of  the  tartar  having 
both  been  destroyed  ;  indeed  the  process  has  for  its  object 
the  preparation  of  a  carbonate  of  potash  from  the  two  salts 
used.  This  flux  disintegrates  ordinary  earthy  or  stony 
matter,  dissolves  silica,  separates  acid  and  sulphur  from 
metals,  assists  in  the  oxygenation  of  many  metals,  and 
dissolves  many  metallic  oxides.  When  charcoal  is  present 
it  decomposes  portions  of  the  flux  and  yields  potassium, 
which  sometimes  combines  with  the  metals  beneath.  An- 
timony, bismuth,  and  some  other  metallic  bodies  thus  be- 
come highly  alloyed  with  potassium*. 

687.  Black.  Flux  is  made  from  a  mixture  of  one  part  nitre 
and  two  parts  crude  tartar,  deflagrated  as  before  in  a 
crucible,  hot  enough  to  cause  feeble  combustion;  the  re- 
sult should  not  be  raised  to  so  high  a  temperature  as  to 
cause  fusion.  From  the  quantity  of  tartar  used,  this  flux 
contains  an  excess  of  charcoal  resulting  from  the  tartaric 
aciti;  hence  it  differs  from  the  white  flux  with  which  it 
would  otherwise  agree,  in  containing  a  reducing  agent. 
The  charcoal  frequently  assists  in  converting  metallic  ox- 
ides into  metals  by  abstracting  the  oxygen.  The  flux  yields 
potassium  in  the  manner  before  mentioned. 

6S8.  Crude  tartar,  argol,  or  cream  of  tartar,  when  de- 
composed by  heat,  yields  a  carbonaceous  carbonate  of 
potash.  It  is  used  sometimes  with  advantage  as  a  flux, 
from  the  accuracy  with  which  it  may  be  mixed  with  the 
pulverized  substance  whilst  in  the  state  of  tartar.  The 
intimate  manner  in  which  the  charcoal  and  potash  of  this 
flux  are  mixed,  causes  the  evolution  of  much  potassium. 
The  action  of  these  carbonaceous  potash  fluxes  is  influ- 
enced by  the  potassium  evolved,  the  reductions  frequently 
depending  to  a  considerable  extent  upon  it. 

689.  Nitre  is  a  salt   frequently  added  to  the   contents 

*  Setullas:  Journal  de  Physique,  xci.  123,  170.    xciii.  115. 
2  P 


314          SAL  ENIXUM — BORAX GLASS  FLUX. 

of  a  crucible  for  the  purpose  of  communicating  oxygen 
to  some  of  the  metals,  and  converting  them  into  oxides. 
Potash  is  left,  which  operates  as  a  solvent  of  the  oxides 
produced,  and  acts,  generally,  as  the  fluxes  already  de- 
scribed. If  the  substances  present  be  such  as  easily 
combine  with  oxygen,  the  nitre  should  be  added  care- 
fully and  gradually,  lest  a  violent  and  sudden  action  be 
occasioned. 

690.  Sal  Enixum  is  an  acid  sulphate  of  potash  formed 
in  the  manufacture  of  nitric   acid.     It  is  powerfully  cor- 
rosive and  cleansing  in  the  crucible,  and  acts  at  first  as 
an  acid  from  the  excess  which  it  contains.     This   excess 
is  soon  either  neutralized  or  driven  off,  and,  when  char- 
coal is  present,  often  occasions  the   production  of  a  sul- 
phuret,  which,  being  injurious  in   certain  experiments,  is 
then  to   be  avoided. 

691.  Borax  being  a  more  expensive  salt  than  the  for- 
mer is  a  flux  more   rarely  used,  and  only  for  the  cleansing 
or   melting   of  the  most    valuable   metals,   such   as   gold, 
rhodium,   &c.     It   is   a   ready   solvent   of  metallic  oxides 
generally,  and  yet  does  not  act  so  rapidly  upon  earthen- 
ware   crucibles   as  potash,    or  alkaline,  fluxes    containing 
carbonate  of  potash.     It  has  little  or  no  action  on  silver? 
gold,  or  platinum   crucibles. 

692.  All  these  fluxes  act  upon  earthen  crucibles,  some 
more  than  others.    They  are  not  used  with  metallic  crucibles 
except  to  dissolve  adhering  impurity,  and  to  cleanse  them. 

693.  Common  flint  glass  is  a  very  good  flux  in  many 
cases,   and  exerts  but  little  action  on   earthen  crucibles. 
But  it  contains  much  oxide  of  lead,  which  is  reduced  if 
any   charcoal   or   combustible  substance   be   present,  and 
even   by   the    access   of  smoke.     Many   metals,   as   iron, 
zinc,  &c.,  and  several  ores,  also   reduce  portions  of  the 
lead,  and  thus  the  buttons  of  these  metals  beneath  such 
a  flux   become   contaminated. 

694.  Green  bottle  glass   is   a   very  serviceable   flux  at 
high  temperatures,   but  when  charcoal  is  present,  it  yields 
iron  ;   even  traces  of  silicium  and  alumium  have  been  ob- 
served in  iron,  previously  pure,  after  being  heated  with  it. 

695.  These  fluxes  are  sometimes  pulverized  and  mixed 


USES  OF  FLUXES OF  CHARCOAL.  315 

with  the  ores  or  other  substances  to  be  acted  upon,  before 
being  introduced  into  the  crucible,  and  sometimes  are  grad- 
ually thrown  into  the  crucible  afterwards.  The  method  to 
be  adopted  must  depend  upon  the  different  circumstances  of 
the  substance  to  be  operated  with,  the  flux,  and  their  mutual 
action.  It  is  necessary  that  care  be  taken  upon  first  intro- 
ducing the  crucible  into  the  fire  that  the  heat  and  action  be 
moderate,  lest  from  thfc  ebullition  which  always  takes  place 
in  consequence  of  the  liberation  of  either  gas  or  moisture,  a 
part  of  the  flux  should  flow  out,  and  thus  a  portion,  even  of 
the  valuable  part  of  the  contents  be  lost.  As  the  ebullition 
diminishes,  more  of  the  mixture  (if  any  remain)  may  be  add- 
ed, and  .when  all  is  in,  and  the  charge  is  less  agitated,  the 
heat  may  be  raised  until  the  metal  be  fused;  or  if  an  action 
is  going  on,  until  the  flux  itself  become  quiet  and  tranquil ; 
a  result  which  generally  indicates  the  cessation  of  chemical 
action. 

696.  In  consequence   of  the   very   common  occurrence 
of  metals   in   the  state  of  oxide,   their   deoxygenation   is 
most   frequently  the   object   of  a  crucible  operation,   and 
carbon    in   one  form   or   another  is    the   agent  generally 
resorted  to.      It  is  for  this  reason  that  tartar  and  black  flux 
are  so  valuable  as  fluxes.     Charcoal  is  frequently  added  to 
the  oxide  to  be  reduced,  in  quantity  greater  than  that  con- 
tained  in   the  flux ;    sometimes  indeed  no    flux  at  all  is 
used,  it  being  actually  injurious  from  its  affinity  for  oxides, 
and  from  being  in  opposition  to  those  affinities  which  assist 
in  reducing  the  metal.     A   charcoal  crucible,  or  a  cruci- 
ble lined  with  charcoal,  is  useful  for  the  reduction  of  some 
oxides,  as  that  of  iron  for  instance*,  and  also  for  the  deoxy- 
genaiion  of    sulphates  and   their  conversion  into  sulphu- 
retsf;    but  in  other  instances,  when   the  oxides   are  in- 
fusible, and  yet  cannot  be  thus  reduced  by  cementation  as 
it  were,  the  charcoal   may   be   pulverized  and  mixed  with 
the  oxide,  and  the  mixture  introduced  into  the  crucible- 
In  these  cases  it   is  generally  best   to  use  a  crucible  lined 
with  a  thin  coat  of  charcoal. 

697.  There   are   several   substances   which  occasionally 

*  Berthier.  Annales  de  Chimic,  xxvii.  24.  fr  Journal  des  Mines,  vii  421 


316  FURNACE  TUBE  OPERATIONS. 

surpass  charcpal  as  reducing  agents;  sometimes  because 
they  mix  more  intimately  with  the  oxide  in  powder, 
and  at  others  because  they  either  are  fluid,  or  melt  when 
heated ;  and  being  absorbed,  are  present  every  where  in 
the  mass,  and  when  decomposed  leave  charcoal  wherever 
they  have  had  access;  but  they  should  be  such  bodies  as 
bear  a  high  heat  without  being  dissipated,  or  when  decom- 
posed leave  much  carbon.  Of  this  kind  are  starch,  gum, 
sugar,  wax,  spermaceti,  oil,  fat,  tar,  and  pitch. 


SECTION  XIV. 
FURNACE  TUBE  OPERATIONS. 

698.  THE  operations  to  be  described  in  this  chapter  are 
such  as  require  a  high  temperature,  like  those  just  referred 
to,  but  being  performed  with   substances  in  either  the  gase- 
ous or  vaporous  state,  require  another  description  of  appa- 
ratus for  their  confinement  and  subjection  to  the  necessary 
heat.     The  vessel  now  to  be  adopted  is  a  tube,  and  by  its 
means  either  gases  or  vapours  may  be  subjected  alone  to 
great  heat,  or  they  may  be  passed  over  solid  or  fluid  bodies 
previously  raised  to  a  high  temperature.     On  both  these 
accounts  the  methods  about  to  be  described  are  very  com- 
mon and  useful. 

699.  Different  tubes  are  required  for  different  occasions. 
They  are  frequently  made  of  earthenware ;    these  resist  a 
high  heat,  except  that  they  are  liable  to  crack  in  the  fire ; 
but  this  fault  may  in  part  be  guarded  against  by  previously 
luting  them,  for  the  reasons  and  in  the  manner  directed 
with  respect   to  earthen  retorts  (491,  1084).     In  addition 
to  the  directions  there  given  for  luting,  it  may  be  observed, 
that,  with  respect  to  tubes,  the  lute,  after  being  put  on  as 
stiff  and  as  tightly  as  possible,  may  be  surrounded  by  a  long 
slip  of  sampler  or  open  canvass,  running  round  it  in  a  spiral 
manner,  so  that  each  fold  may  overlap  the  last  (1094):  this 


FURNACE  TUBES IRON PLATINUM.          317 

will  retain  the  lute  in  its  place  during  desiccation,  and 
prevent  the  occurrence  of  cracks*.  The  porosity  of  earth- 
enware has  been  before  mentioned  (489,  491),  and  if  ne- 
cessary must  be  guarded  against  as  much  as  possible  by 
washing  the  tube  with  borax,  &c.,  as  already  directed 
(491).  But  when  the  loss  of  a  part  of  the  gas  is  of  little 
importance,  as  when  it  is  passed  into  a  tube  to  operate 
upon  the  substance  within,  without  reference  to  quantity, 
then  the  porosity  of  the  tube  does  not  much  interfere. 
Wedgwood's  tubes  are  of  pure  ware,  but  very  liable  to 
crack.  Tubes  of  the  same  material  as  that  used  in  the 
manufacture  of  common  English  crucibles  are  not  so  subject 
to  this  failure,  but  are  more  porous.  Black  lead  tubes,  or 
such  as  are  made  of  a  mixture  of  clay  and  plumbago, 
are  least  liable  to  crack  of  any,  but  sometimes  communi- 
cate iron,  and  are  very  porous.  These  tubes  are  fre- 
quently bent  into  the  form  of  a  narrow  U,  when  they 
may  be  readily  introduced  into  the  mouth  of  a  common 
furnace,  the  two  ends  and  apertures  being  outwards,  and 
close  together.  When  straight  it  is  advantageous  to  guard 
them  in  the  furnace  by  a  semi-cylinder  of  tin-plate,  and  at 
times  they  are  conveniently  strengthened  by  being  passed 
through  a  cylinder  of  plate-iron,  roughly  turned  into  a  form 
which  may  serve  as  a  casing. 

700.  Iron  tubes  are  constantly  useful.    A  gun-barrel,  when 
convenient  as  to  size,  answers  the  purpose  very  well.     When 
larger  or  smaller  tubes  are  necessary  they  must  be  forged  for 
the  occasion.     If  required  for  a  long  operation,  or  at  a  tem- 
perature above  a  red  heat,  they  should   be  protected  from 
the  fire  either  by  luting  (699),  or  by  being  passed  through  a 
black  lead  tube.     Iron  tubes  are  generally  adapted  for  the 
decomposition  of  organic  substances,  as  oils,  &,c.,  or  water, 
or  potash  by  charcoal  or  iron,  or  of  gases  that  have  little  or 
no  action  upon  the  metal,  as  ammonia  and  carburetted  hy- 
drogen. 

701.  A  platinum  tube  can  scarcely  be  dispensed  with  in 
the  laboratory,  because  of  the  very  high  temperature  it  will 

*  Mr  Cooper's  Practice  and  Suggestions. 


318          FURNACE  TUBES — COPPER — GLASS. 

bear,  and  the  few  instances  in  which  it  interferes  with  the  sub- 
stance passed  through  it:  substances  may  be  heated  together 
in  it  which  cannot  be  so  treated  in  any  other  kind  of  vessel. 
Chlorine,  sulphur, and  the  metals,  are  almost  the  only  bodies 
which  affect  it;  oxygen  and  acid  gases  have  no  power  of  action 
on  it.  Those  are  best  which  are  drawn,  and  have  no  joint 
down  the  side,  but  they  are  the  most  expensive.  Those  which 
are  turned  or  bent,  and  soldered  with  gold,  will  not  bear  the 
high  temperature  of  the  former,  and  it  is  impossible  to  make 
a  joint  without  solder,  which  will  continue  tight.  The 
platinum  tube  may  often  be  used  with  advantage  as  a  retort, 
by  the  adaptation  of  a  plug  to  one  end,  which  may  be  removed 
or  replaced  at  pleasure. 

702.  A  bored  copper  tube  is  frequently  used  when  a  pla- 
tinum tube  is  not  at  hand,  but  it  is  limited  as  to  the  tem- 
perature it  will  sustain,  and  also  as  to  the  substances  which 
may  be  passed  through  it. 

703.  Glass  tubes  are  perhaps  the  most  generally  useful  of 
all.     They  allow  operations  performed  in  them  to  be  watched 
up  to  a  red  and  even  a  yellow  heat,  and  some  kinds  of  glass 
resist  the  action  of  most  chemical  agents  likely  to  be  brought 
into  contact  with  them  in   this  form.     The  best  tubes  are 
those  made  of  green  bottle  glass,  they  require  care  in  heating, 
but  resist  the  action  both  of  heat  and  chemical  agents  much 
better  than  those  of  flint  glass.     The  latter  include  in  their 
composition  both  alkali  and  oxide  of  lead,  substances  which 
are  liable  to  be  acted  upon   in    many  experiments.     They 
soften  also,  and  are  easily  expanded,  and  collapsed  at  a  red 
heat,  but  to  compensate  in  part  for  these  bad  qualities,  they 
may  be  obtained  any  where,  whereas  green  glass  tubes  are 
very  scarce.     When  of  small  size  they  are  readily  bent  into 
form,  and  arranged  by  a  spirit-lamp  and   mouth   blow-pipe. 
Class  tubes  may,  like  those  of  earthenware,  be  strengthened 
by  luting,  but  it  is  generally  so  desirable  to  witness  the  ac- 
tion going  on  within,  that  a  semi-cylinder  of  tin  plate,  or  of 
earthenware,  will  be  found  a  more  advantageous  support.* 

704.  The  method  of  connecting  these  tubes,  when  in  the 

*  The  wire-gauze  support  suggested  by  Professor  Hare  is  more  elegant,  and 
much  safer. — Ed. 


JUNCTIONS METALLIC GLASS  TUBES.  319 

furnace  with  parts  of  other  apparatus  by  which  the  gas  or 
vapour  is  either  to  be  introduced  or  conveyed  away,  must  vary 
with  the  substance  of  the  tubes.  They  should  be  of  such 
length  as  to  leave  the  ends  projecting  sufficiently  far  from 
the  furnace,  to  be  either  of  moderate  temperature,  or  to  allow 
of  the  application  of  cooling  processes;  which,  however, 
should  only  be  applied  to  metallic  tubes,  and  then  with  cau- 
tion. When  the  tubes  are  metallic,  terminating  pieces 
with  ground  joints  or  screws  may  be  brazed  or  welded  on, 
and  thus  junctions  are  easily  effected;  and  in  these  cases 
if  the  ends  be  hot,  washers  of  card  should  be  applied  at  the 
screw  (830),  and  not  such  as  are  made  of  oiled  leather;  for 
the  latter  are  gradually  decomposed  and  become  unsound. 
It  is  often  of  use  in  operations  with  the  gun-barrel,  to  termi- 
nate it  at  each  end  by  a  stop-cock,  of  which  the  outer  ex- 
tremity has  been  formed  into  a  ground  socket;  perforated 
wooden  or  cork  plugs,  formed  at  one  end  so  as  to  fit  tightly 
into  these  sockets,  and  at  the  other  into  a  screw,  may  then 
be  used  as  adapters;  while  they  complete  the  junction,  they 
prevent  the  transmission  of  heat. 

705.  If  the  tube  be  of  earthenware  or  glass,  and  the  ex- 
tremity be  cool,  the  junction  may  be  effected  by  fitting  on 
a  cap  (833),  or  by  a  perforated  cork,  or  by  caoutchouc  con- 
necters* (449),  or  by  any  of  the  processes  already  described, 
or  to  be  described  in  the  sections  on  gaseous  manipulation, 
and  on  lutes  and  cements.     If  the  terminations  be  hot,  the 
object  must  be  attained  by  applying  some  of  the  methods 
described  in  the  latter  section. 

706.  When  vapours  are  to  be  passed  through  a  heated 
tube,  it  will  be  necessary  to  generate  them  in  a  little  boiler 
or  a  retort,  connected  with  one  end  of  the  tube.     In  such  a 
case  the  joint  must  be  capable  of  bearing  the  heat  requisite 
for  the  existence  of  the  vapour,  and  the  neck  of  the  retort 
and  the  associated  part  of  the  tube  should  be  wrapped  up  in 
flannel  or  paper  (473),  that  loss  of  heat,  and  consequent 
condensation  of  the  vapour  there,  may  be  prevented  as  much 
as  possible. 

*  It  is  not  necessary  to  use  caoutchouc  tubes  as  connecters.  A  piece  of  sheet 
gum  elastic  wrapped  tightly  round  the  juncture,  and  tied,  affords  more  security 
and  the  process  is  more  easily  completed.— ED. 


320  HEATING  TUBES  IN  FURNACE — LAftlP. 

707.  The  adaptation  of  furnaces  to  the  heating  of  these 
tubes  will  be  readily  understood.  When  crucible  furnaces 
are  used,  the  tube  should  be  placed  in  two  notches  (158) 
cut  in  opposite  sides,  so  as  to  bring  the  upper  part  of  the 
tube  below  the  level  of  the  edges,  and  the  grate  should  be 
raised  to  within  one  inch  and  a  half  of  the  tube  itself.  If 
one  furnace  be  scarcely  wide  enough  to  heat  a  sufficient 
length  of  tube,  a  second  may  be  arranged  by  its  side,  the 
tube  passing  through  the  notches  and  lying  over  both.  It 
is  easy,  by  piling  the  charcoal  over  the  edges  of  the  furnaces 
where  they  touch,  to  heat  the  tube  there ;  and  a  brick  or 
tile,  or  other  body,  should  be  put  on  each  side,  bearing 
against  the  two  furnaces,  for  the  purpose  of  interfering  with, 
and  as  far  as  may  be,  preventing  the  current  of  air,  which 
will  otherwise  pass  towards  the  junction,  and  in  ascending 
tend  to  cool  the  tube  at  that  part. 

708.  By  placing  two  bricks  edgewise  across  a  loose  square 
grate,  four,   five,  or  six  inches  distant  from  each  other,  a 
space  is  left  between  them,  which  makes  an  excellent  tube- 
furnace  ;  it  may,  by  the  use  of  several  bricks,  be  arranged 
to  heat  any  desired  length  of  tube.     Charcoal  is  to  be  the 
fuel  used.     But,  when  a  much  higher  heat  is  necessary,  and 
even  the  application  of  a  blast  required,  as  in  the  prepara- 
tion of  potassium,  it  is  better  to  build  up  a  temporary  fur- 
nace with  bricks  and  mortar,  setting  the  tube  in  its  proper 
position  in  the  course  of  the  work ;  and  as  the  brickwork  is 
not  required,  nor  is  likely  to  be,  of  much  durability,  it  will 
fre  safe,  before  putting  a  fire  in,  to  tie  it  round  with   iron 
wire.     When  the   heat  is  to  be  raised  to  a  high  degree,  it 
will  be  proper  to  introduce  a  stay  or  two,  pieces  of  black 
lead  tube  for  instance,  as  supporters  to  the  lute. 

709.  A  small  piece  of  glass  tube  may  be  heated  in  a  spir- 
it-lamp, and  a  greater  portion  in  the  oil-lamp  (212).     The 
tube  may  either  go  through  holes  in  the  sides  of  the  chim- 
ney, just  above  the  top  of  the  flame,   or  it  may   be  bent 

thus    M  so  as  to  pass  down  the  chimney,  until  the  lowest 
part  of  the  tube  is  just  above  the  flame.     The  concentric 


COOPER'S  LAMP  FURNACE. 


double-wick  oil-lamp  (213),  or  the  large  spirit-lamp  (205, 
206),  answers  for  these  purposes  very  well. 

710.  The  lamp  which  surpasses  all  others  for  the  ignition 
of  a  length  of  tube,  is  that  invented  by  Mr  Cooper*,  and 
figured  in  the  accompanying  wood-cut.  It  consists  of  a 
frame  ten  or  eleven  inches  long,  which,  being  raised  upon 
four  feet,  has  an  aperture  from  end  to  end  of  0.8  or  0.9,  of 
an  inch  in  width.  It  is  furnished  at  each  end  with  a  wire 
support,  adjustible  in  its  height,  and  bent  at  the  top  into  a 
convenient  form  for  retaining  a  tube  in  a  horizontal  position. 
The  lamps  are  two  in  number,  and  stand  on  the  frame,  one 
on  each  side  the  aperture.  They  have  each  ten  burners  pass- 


o 


ing  obliquely  upwards  from  one  edge  and  inclining  towards 
those  of  the  other  lamp,  over  the  aperture  before  mentioned. 
Each  burner  is  0.8  of  an  inch  in  length,  half  an  inch  wide, 
and  about  that  distance  apart  from  its  neighbours,  and  the 
lamps  may  be  put  so  near  to  each  other  as  to  leave  the  two 
sets  but  little  asunder,  or  they  may  be  removed  to  a  greater 
distance.  Small  uprights  are  fixed  on  the  top  of  the  lamps 
between  the  burners  :  there  is  also  a  feed-pipe  to  each  lamp 
closed  by  a  cork,  and  each  burner  is  furnished  with  a  cap,  to 
cover  it  and  prevent  the  evaporation  of  alcohol  when  the 

*  Transactions  of  the  Society  of  Arts,  xll,  p,  56.     Quarterly  Journal,  xvii., 
p.  232. 

2  Q 


322  COOPER'S  LAMP  FURNACE. 

lamp  is  not  in  use.     The  whole  of  this  apparatusis  made  of 
tin-plate  and  iron-wire.* 

711.  The  trimming  of  the  lamps  is  performed  by  selecting 
some  straight  Argand  lamp-cottons,  and  cutting  off  so  much 
from  both  edges  of  the  folded  cotton  as  will  divide  it  into 
two  pieces,  each  of  proper  width  to  pass  down  the  burners. 
The  waxed  end  is  introduced  first,  and  the  cotton  thrust  in 
until  it  touches  the  opposite  side  at  the  bottom  ;  this  is  easily 
done,  and  then  the  excess  of  cotton  above  is  to  be  cut  off  with 
scissors.     The  caps  are  then  put  on,  and  alcohol  introduced 
at  the  feeding  aperture,  until  the  lamps  are  two-thirds  or 
three-fourths  full,  when  they  are  ready  for  use. 

712.  A  platinum  tube  of  half  an  inch  in  diameter  may  be 
heated  to  full  redness  by  this  lamp-furnace  in  a  few  minutes.f 
For  this  purpose  it  is  to  be  sustained  at  the  two  ends  by  the 
wire  supports  already  mentioned,  these  being  adjusted  so  as 
to  leave  an  interval  of  about  an  inch  between  the  tube  and 
the  double  line  of  wicks  beneath.     The  lamps  are  then  to 
be  lighted  and  the  cottons  adjusted,  until  the  flames  reach 
and  wrap  about  half  way  round  the  tube.     The  lamps  should 
be  placed  so  as  to  leave  about  half  an  inch  between  the  two 
rows  of  wicks;  so  that  air  passing  upwards  from  beneath  the 
frame,  and  through  the  aperture  before  mentioned,  may  as- 
cend between  the  flames  and  assist  in  supporting  the  com- 
bustion.    The  flames  will  coalesce  over  this  aperture,  and 
also  from  side  to  side,  so  as  to  furnish  a  powerful  and  contin- 
uous line  of  intense  heat,  by  the  time  they  have  ascended  to 

*  It  is  scarcely  credible  that  such  a  lamp  could  he  used  for  a  lengthened  pro- 
cess or  indeed  for  many  minutes,  without  giving  a  wasteful  and  inconvenient 
temperature  to  the  alcohol.  To  prevent  such  effects,  the  Editor  uses  oblong, 
square  lamps,  with  corresponding  central  excavations  passing  vertically  through 
and  through,  in  which  are  set  one  or  more  burners  nearly  as  long  as  the  cavity, 
and  which  have  communication  with  the  alcohol  solely  by  tubes  placed  at  the 
bottom  of  the  cistern.  The  distance  and  diminutiveness  of  the  connecting  pipes 
entirely  prevent  the  elevation  of  the  temperature  of  the  alcohol.  With  such 
lamps,  and  with  tubes  of  glass  protected  by  Dr  Hare's  wire  supports,  a  great  va- 
riety of  chemical  researches  may  be  conducted. — ED. 

f  In  consequence  of  the  peculiar  powers  of  that  metal,  platinum  tubes  or  cru- 
cibles are  more  easily  heated  by  alcohol  than  those  of  either  iron  or  glass.  At  a 
moderate  temperature  the  platinum  causes  the  more  rapid  combination  of  the  al- 
coholic vapours  with  atmospheric  oxygen. — ED. 


COOPER'S  LAMP  FURNACE.  323 

the  tube.  By  uncovering  and  using  only  so  many  wicks  as 
are  beneath,  and  proportionate  to,  the  part  of  the  tube  to 
be  heated,  a  certain  part  of  its  length  may  be  subjected  to 
a  high  temperature  at  once. 

713.  It  is  desirable  in  numerous  cases  to  apply  the  flame 
successively  from  one  end  of  the  tube  to  the  other.    On 
these  occasions  the  operation  must  commence  with  all  the 
wicks  uncovered.     As  many  are  then  to  be  lighted  as  may 
at  first  be  requisite,  and  to  prevent  the  combustion  from 
spreading  to  the  contiguous  uninflamed  wicks,  a  slip  of  tin- 
plate,  about  three-fourths  of  an  inch  high,  is  to  be  placed 
across  under  the  tube,  and  supported  by  the  burners  and  the 
upright  pieces  (710)  already  mentioned.    The  heat  having 
been  continued  sufficiently  long  on  the  one  part,  the  tem- 
porary tin  division  is  to  be  removed  farther  on,  more  wicks 
are  to  be  lighted,  and  if  any  of  those  at  the  opposite  end 
are  now  unnecessary,  a  similar  plate  of  tin  should  be  put 
between  them  and  those  which  are  still  to  continue  in  com- 
bustion, and  the  former  extinguished  by  a  sudden  slight  puff 
of  the  breath. 

714.  Mr  Cooper  has  occasionally  constructed  the  lamps  in 
such  a  manner,  that  each  burner  has  its  separate  receptacle 
of  alcohol,  so  that  in  place  of  one  long  lamp  like  that  de- 
scribed, it  appears  to  consist  of  many  small  lamps,  standing 
side  by  side,  but  independent  of  each  other.     When  only  a 
part  of  the  tube  is  to  be  heated  at  once,  a  few  only  of  the 
lamps  are  lighted,  and  these,  without  using  the  rest,  are 
easily  moved  one  way  or  the  other,  and  their  flames  applied 
successively  under  all  parts  of  the  tube. 

715.  The  lamps  cannot  heat  a  greater  length  of  tube  at 
once  than  is  equal  to  the  length  of  the  frame;  but  there 
is  no  difficulty  in  putting  two  or  more  frames  together  end 
to  end,  and  in  that  manner  igniting  any  extent  of  tube.     If 
it  be  required  to  heat  a  tube  longer  than  the  frame,  but  in 
successive  portions,  it  is  easily  done  by  shifting  the  tube 
itself  through  the  apertures  in  the  wire  supporters  by  which 
it  is  held  (710). 

716.  When  small  metal  tubes,  or  moderately-sized  tubes 
of  glass  are  to  be  heated,  a  single  row  of  wicks  is  required, 
which  must  be  advanced  a  little  to  the  edge  of  the  aper- 


324 

ture,  that  the  flames  may  rise  up  just  beneath  the  tube. 
Green  glass  tubes  are  constantly  in  use  witli  this  apparatus, 
and  in  some  cases,  when  the  advantage  of  seeing  the  inte- 
rior is  of  no  consequence,  it  is  advisable,  for  many  reasons, 
to  inclose  them  in  a  tube  of  copper  foil  (1351);  this  supports 
the  glass  when  so  hot  as  to  become  soft,  confines  and  pre- 
vents it  from  being  expanded  into  bulbs  by  the  pressure  of 
gas  within,  and  assists  in  conducting  the  heat  uniformly 
over  the  tube.  It  also  conveys  heat  to  those  parts  of  the 
tube  not  yet  subjected  to  the  flame,  and  by  gradually 
warming,  prepares  them  for  its  application;  so  that  no  sud- 
den change  of  temperature  is  ever  occasioned,  and  the  tube 
is  consequently  more  safely  heated.  This  external  case  is 
made  of  a  slip  of  copper  foil,  about  an  inch  or  an  inch 
and  a  half  wide,  and  so  thick  that  twenty-five  or  thirty  folds 
squeezed  by  pincers  may  be  equal  to  about  the  tenth  of  an 
inch.  The  foil,  after  being  flattened,  should  be  rolled  up 
tightly  into  a  small  cylinder,  bound  with  a  piece  of  wire, 
and  heated  to  dull  redness  for  a  moment,  to  destroy  the  de- 
gree of  rigidity  given  to  it  by  pressure  between  the  rollers. 
Being  then  cooled  and  opened  out,  it  is  to  be  wrapped  close 
round  the  part  of  the  tube  to  be  heated  in  a  spiral,  one  fold 
overlapping  another  at  the  edge.  When  so  much  of  the 
tube  is  enveloped  as  is  required,  the  extra  length  of  foil  is 
to  be  torn  off,  and  the  end  kept  tight  upon  the  tube  by 
a  turn  or  two  of  thin  wire.  The  case  thus  formed  is 
more  or  less  thick,  and  consequently  strong,  in  proportion 
to  the  degree  in  which  the  turns  are  folded  over  each  other. 
If  a  fold  overlap  the  previous  one  by  one  half,  then  the  case 
will  be  of  double  thickness;  if  it  overlap  two-thirds,  of 
triple  thickness;  if  it  overlap  but  a  little  at  the  edges, 
the  case  will  consist  of  little  more  than  a  single  thick- 
ness of  foil. 

717.  Glass  tubes,  whether  guarded  in  this  way  or  not, 
generally  require  support  in  the  middle  to  prevent  them 
from  bending.  This  support  is  given  by  a  moveable  stand, 
made  of  a  piece  of  iron  wire  fixed  perpendicularly  into  a 
leaden  bottom,  and  terminating  above  in  a  loop  or  ring, 
or  sometimes  in  a  crutch.  This  wire  passes  up  the  aper- 
ture between  the  lamps,  and  may  be  moved  along  the 


TUBE DECOMPOSITION.  325 

tube  between  the  flames  into  the  most  effectual  or  con- 
venient position.  Even  short  pieces  of  tube  closed  at 
one  end  may  be  supported  by  means  of  it  and  heated; 
it  is  also  useful  in  the  arrangement  of  other  tubes  as 
well  as  those  which  are  straight. 

718.  When  gases  or  vapours  are  to  be  passed  through 
tubes  at  high  temperatures,   for  the  purpose  of  effecting 
their   decomposition,  it   will  be  advantageous  to  increase 
the  surface  of  contact,    and  also   to  break  the  uniformity 
of  current  within.     Broken  rock  crystal,  or  flint,  answers 
this  purpose  very  well  with  glass  or  earthenware   tubes. 
The  crystal  or  flint  should  be  divided   in  a  mortar   into 
coarse    particles,   if    the  tube  be   large,    or   if    much  de- 
posited  matter   be   expected   from   the   decomposition;    or 
into  smaller,  if  the  tube  be  small,  or  if   but  a  slight  ac- 
tion, accompanied  with  little  deposit,  be  anticipated.      A 
crumpled  piece  of  wire  should  be  thrust  into  the  tube  near 
to  one  end,  a  few  large   pieces  of  the  broken   substance 
dropped  in  at  the  other  to  rest  upon  the  wire,  and  after- 
wards, that  which  is  considered  of  a  proper  size  is  to  be 
poured  in.     If  two  or  three  larger  pieces,  and  then  more 
wire  be  added,  they  will  retain  the  charge*  in  its  place ; 
but  the  wire  should  be  such  as  will  not  injure  the  expe- 
riment, for  which  reason  also  it  is  better  to  place  it  gene- 
rally out  of  the  heated  part.     Platinum  wire  answers  the 
purpose   for  small  glass   tubes,  and   will    rarely   occasion 
harm.  ' 

719.  Some  substances  have  singular  powers  in  influenc- 
ing  the  decomposition  and  even   combination  of  gaseous 
bodies  and  vapours,  although  they  have   no  apparent  ten- 
dency to  combine  with  either  the  compounds  or  their  ele- 
ments;   and  it   is  for   this    reason  that   tubes  of  different 
substances    operate    differently    upon     the    gases    passed 
through  them.     If  ammoniacal  gas  be  passed  into   a  red 
hot  iron  tube,  it  will   be   easily   decomposed  into   nitro- 
gen and  hydrogen  gases ;  but  if  it  be  passed  through  a 
glass  tube,  as  Gay  Lussac  has  shown,  it  resists  an  equal  and 
even  a  much  higher  temperature,  with  scarcely  any  change. 
This  effect  may  perhaps  be  dependant,  as  MM.  Despretz 
and  Savart  have  endeavoured  to  show,  upon  an  actual  com- 


326       POWER  OF  SPONGY  PLATINUM — HYDROGEN  BY  STEAM. 

bination  occurring  between  the  metal  and  some  of  the  sub- 
stances present ;  but  whatever  the  cause,  it  may  be  taken 
advantage  of  without  the  necessity  of  having  tubes  formed  of 
the  materials,  it  being  sufficient  to  introduce  them  into 
glass  tubes  in  the  manner  before  described  for  rock 
crystal  (718) ;  it  will  be  found  that  a  glass  tube  charged 
with  broken  iron  turnings,  will  as  effectually  cause  the  de- 
composition of  ammonia  as  one  of  iron. 

720.  The  power  ofspongy  platinum  is  such  that  it  occasions 
the  combination  of  oxygen   and   hydrogen,  even  at  com- 
mon temperatures,  producing  ignition  and  explosion.     When 
its  action  is  diminished  by  mixture  with  earthy  bodies,  it  is 
again  increased  by  elevation  of  temperature.     Spongy  pla- 
tinum also  causes  the  union  of  oxygen  and  oxide  of  carbon 
at  common  temperatures;  the  decomposition  of  nitric  oxide 
by  hydrogen;  and  the  combination  of  both  the  elements  of 
olefiant  gas  with  oxygen,  at  temperatures  above  572°.     For 
further  illustrations  of  this  power  of  the  metals,  see  Dulong 
and  Thenard's  paper  in  the  Annales  de  Chimie,  xxiii.  440. 

721.  The  vapour  of  water  passed  over  iron  heated  in  tubes 
is  decomposed,  the  metal  becomes  oxidized,  and  hydrogen 
gas  is  evolved.     In  this  case  the  higher  the  temperature,  the 
more  rapid  is  the  action.     The  steam  should  be  raised  from 
a  small  boiler,  and  not  in  too  large  a  quantity,  as  great  ex- 
cess tends  to  cool  the  tube  considerably.     If  one-third  or 
one-half  of  what  is  passed  into  it  be  decomposed,  it  is  in 
sufficient  proportion.     The  iron  for  small  experiments  may 
very  conveniently  be  clean  turnings,  beaten  into  small  pieces 
in  a  mortar.     They  lie  close,  expose  much  surface,  and  keep 
open  a  free  passage  for  air.* 

*  When  vapour  ofwater  is  to  be  decomposed  by  iron  heated  in  a  glass  tube, 
the  cul  de  sac  of  the  sealed  end  of  the  tube  may,  by  being  bent  downwards, 
supply  the  place  of  a  boiler.  The  boiler,  as  commonly  used,  is  not  the  most  con- 
venient, because  the  least  safe,  and  most  difficultly  regulated  method  of  supplying 
the  vapour.  Any  apparatus  which  will  cause  water  to  enter  the  gun-barrel,  or 
other  iron  tube  drop  by  drop,  is  preferable.  By  inflecting  one  end  of  tube  up- 
wards, and  dropping  water  into  it  either  by  means  of  Hare's  chyometer,  a  good 
syringe,  or  a  stop-cock  [and  funnel,  a  surprizingly  beautiful  effect  is  obtained. 
For  class  demonstration,  the  best  mode  is  that  which  most  clearly  exhibits  the 
minuteness  of  the  quantity  of  water  necessary  for  the  production  of  a  great  vol- 
ume of  hydrogen.  For  that  purpose  seal  at  one  end  a  small  glass  tube,  about 
two  or  three  inches  long ;  bend  it  near  the  middle  slightly,  and  after  tilling  the 


TUBE  DECOMPOSITION — COMBINATIONS.  327 

722.  The  vapours  of  alcohol  and  ether  may  be  decomposed 
in  a  similar  manner:  iron  assists,  but  is  not  necessary;  but 
rock  crystal,  orsome  substance  affording  surface  (718)  should 
be   introduced.    The   results  vary   with   the   temperature. 
Nearly  all  the  vapour  that  is  sent  in  should  be  decomposed. 
It  may  be  generated  in  a  little  boiler,  or  in  a  flask  or  retort, 
and  caoutchouc  junctions  may  be  used,  even  with  ether. 

723.  Olefiant  gas,  nitrous  oxide,  and  some  other  gases, 
are  decomposed  by  being  passed  through  heated  tubes.    If 
the  general  facts  are  only  to  be  observed,  the  gases  may  be 
introduced  from  the  retort  evolving  them,  or  forced  in  from  a 
bladder  or  an  air-tight  caoutchouc  bag  (820,  821),  and  the 
contents  may  even  be  received  in  similar  vessels  at  the  other 
end  of  the  tube:  but  if  accurate   experiments  upon  precise 
quantities  are  required,  then  two  mercurial  gazometers  (809) 
should  be  connected  with  the  tube,  that  nothing  may  be 
lost. 

724.  Many  oxides  may  be  reduced   in  part  or  entirely 
when  heated  in  tubes,  by  passing  certain  gases  or  vapours 
over  them.     Protoxide  of  manganese  is  best  obtained  in  this 
way  from  a  pure  peroxide,  or  from  the  oxide  precipitated 
from  a  pure  salt;  hydrogen  passed  over  it  at  a  red  heat  redu- 
ces every  particle  to  the  state  of  dry  protoxide,  and  the  pro- 
gress of  the  change  from  one  end  of  the  tube  to  the  other 
is   beautifully    exhibited.     Oxides  of   titanium,    tungsten, 
chromium,  iron,  &c.,  are  often  usefully  treated  in  this  man- 
ner; and  besides  hydrogen,  other  reducing  agents  may   be 
used.     Ammonia  has  equal  power  with  hydrogen,  and  some- 
times, from  the  nascent  state  of  the  hydrogen  in  it,  is  supe- 
rior to  the  simple   gas.     The   vapours  of  alcohol,    ether, 
naphthaline,  and  camphor,  may  be  used,  where  it  is  probable 
that   carbonaceous   matter  will   favour  the    desired    effect 

725.  Many  combinations  are  effected  with  great  advan- 
tage in  a  heated  tube.     Thus  oxygen  is  easily  combined 
with  baryta,  and  the  peroxide  of  barium  formed.     The  heat 

sealed  leg  with  water,  insert  the  open  end  through  the  aperture  of  a  cork  fixed  in 
one  extremity  of  an  iron  tube.  Heat  will  immediately  drive  over  a  portion  of 
steam,  and  the  water  remaining  will  indicate  the  quantity  employed  in  produc- 
ing the  hydrogen,  which  may  also  be  measured.— ED. 


328         SULPHURET  OF  PLATINUM PHOSPHURET  OF  LIME. 

should  be  a  dull  red;  no  oxygen  will  pass  till  the  whole  of 
the  earth  is  peroxidized.  In  such  cases,  the  end  of  the  tube 
at  which  the  oxygen  passes  out  does  not  require  to  be  con- 
nected with  any  apparatus;  a  glowing  match  should  now  and 
then  be  applied  to  it,  and  when  the  presence  of  pure  oxy- 
gen is  evident,  the  operation  is  finished. 

726.  Sulphur  may  be  combined  with  platinum,  and  phos- 
phorus with  lime,  in  a  tube  apparatus,  with  great  convenience. 
The  platinum  in  the  spongy  state,  or  the  quick  lime,  are  to 
be  placed  in  the  tube,  and  heated  to  dull  redness;  the  tube 
should  be  slightly  inclined,  and  the  higher  end  lengthened 
so  far  from  the  furnace  or  lamp,  as  to  be  only  warm.  If 
turned  up,  it  is  an  advantage,  and  the  aperture  there  should 
be  fitted  by  a  good  cork.  When  the  tube  is  sufficiently 
heated,  a  piece  of  sulphur  in  the  one  case,  or  a  piece  of  phos- 
phorus in  the  other,  is  to  be  dropped  or  thrust  in  at  this  end, 
and  the  aperture  immediately  closed  by  the  cork.  A  small 
spirit-lamp  flame  will  melt  the  substance,  and  cause  it  to  run 
down  to  the  warm  part,  where  it  will  gradually  become  va- 
pour; and  though  a  part  may  distil  back  (which  is  of  no 
consequence),  the  greater  portion  will  be  sent  over  the  pla- 
tinum or  lime  within:  the  progress  of  the  change  will  easily 
be  observed.  When  the  first  portion  of  substance  has  com- 
bined, a  second  is  to  be  introduced;  the  aperture  being  rapid- 
ly opened  and  closed,  so  that  no  current  may  be  allowed  to 
occur  in  the  tube,  and  this  process  is  to  be  continued  until 
the  substance  within  is  entirely  converted  into  sulphuret  or 
phosphuret.  Great  care  is,  of  course,  required  in  handling 
the  phosphorus;  pieces  not  more  than  one-third  or  the  half 
of  an  inch  in  length,  should  be  introduced  at  once  into 
tubes  half  an  inch  in  diameter.  They  should  first  be  dried, 
then  dropped  in  rapidly  by  a  pair  of  forceps,  lest  the  temper- 
ature of  the  tube  should  be  sufficient  to  inflame  them.  In 
wiping  phosphorus  dry,  it  should  be  rolled  between  two  or 
three  folds  of  cloth  or  filtering  paper,  every  part  of  its  surface 
being  pressed  but  not  rubbed;  and  when  thus  dried,  it  must 
not  be  held  in  the  uncovered  hand,  but  be  inclosed  in  cloth 
or  paper,  and  be  taken  out  from  them  by  the  forceps.  This 
is  to  be  done  at  some  little  distance  from  the  furnace  or 


WATER  PNEUMATIC  TROUGH.  329 

lamp,  and  when  the  phosphorus  is  carried  towards  the  heat, 
the  operation  should  be  conducted  quickly,  though  steadily, 
that  no  time  be  allowed  for  the  temperature  of  the  substance 
to  rise  so  high  as  to  cause  its  inflammation  before  it  be  in 
the  required  situation. 

727.  Titanium  may  be  combined  with  chlorine  by  passing 
the  gas  over  the  metal  in  a  heated  tube.*  The  alkaline 
earths  may  be  decomposed  by  passing  chlorine  over  them  in 
the  same  manner,  oxygen  being  then  evolved,  and  their  bases 
remaining  combined  with  the  chlorinef :  numerous  other  che- 
mical actions  of  the  most  important  kind  may  be  effected  by 
this  mode,  in  a  manner  the  most  convenient  possible  for  ob- 
servation. When  the  substance  used  and  the  results  produ- 
ced are  equally  fixed,  small  platinum  trays,  formed  by  doub- 
ling a  piece  of  foil,  may  be  used  for  containing  them;  they 
are  easily  introduced  into  the  tube  and  withdrawn  again  by 
a  wire  bent  into  a  hook  at  the  extremity.  Every  facility  is 
afforded  for  conducting  away  the  results,  whether  solid, 
fluid,  or  gaseous;  and  in  by  far  the  greater  number  of  cases, 
those  excellent  flexible  connecters  formed  of  caoutchouc 
(449)  are  of  perfect  and  easy  application. 


SECTION  XV. 

PNEUMATIC  MANIPULATION   OR   MANAGEMENT 
OF   GASES. 

§  1.  Pneumatic  Troughs,  Jars,  fyc. 

•  728.  THE  first  apparatus  necessary  for  the  experimental 
practices  to  which  this  chapter  relates  is  the  pneumatic 
trough,  with  its  accompanying  jars.  We  are  indebted  to 
Priestley  for  the  invention  of  this  useful  vessel,  and  for  much 
of  the  apparatus  which  is  used  in  conjunction  with  it. 

*  Mr  George,  Annals  of  Philosophy,  New  Series,  ix.  18. 

t  Sir  H  Davy,  Phil.  Trans.  1811,  p.  12. 
2  R 


330 


COMMON  PNEUMATIC  TROUGH. 


729.  The  common  pneumatic  trough  is  a  vessel  construct- 
ed so  as  to  retain  water,  and  of  such  dimensions  that  large 
jars  may  be  filled  in  it;  and  it  is  finished  with  shelves  or  sup- 
ports beneath  the  surface  of  the  water,  on  which  vessels  may 
firmly  stand.     The  trough   is  frequently  so  contrived,  that 
the  shelf  is  of  considerable  extent,  and  the  deeper  part,  which 
may  be  called  the  well,  made  of  such  dimensions  as  just  to 
allow  the  filling  of  the  largest  jar  required  for  use.     This  is 
of  no  consequence  as  regards  the  level  of  the  water,  and  its 
alteration  by  filling  jars,  and  raising  them  upon  the  shelf; 
but  it  is  of  importance  that  the  well  should  be  sufficiently 
large.      There  should   be  width  and  breadth  enough    for 
two   or  three  jars  to  be  immersed  at  once,  and  sufficient 
depth  to  permit  the  inversion  of  any  jar  or  tube  beneath 
the  surface,  likely  to  be  in  use  at  the  trough.     The  shelf 
also  of  the  large  trough   should  be  of  sufficient   size   to 
hold  several  jars  of  gas  at  once.     If  the  surface  of  water 
be   19    inches  by  28,  and  a  well    be  formed   at  one  end 
of  14  inches  by  10,  and  12  inches  in  depth,  so  as  to  leave  a 
continuation  of  the  shelf  surface  on  three  sides  of  the  well, 
of  two  inches    and  a  half  in  width,    it  will  be    found  suffi- 
ciently large  for  almost  every  purpose. 

730.  Such  a  trough  is  best  made  of  japanned  copper, 
and  supported  in  a  wooden  frame,  so  as  to  stand  about  39 
inches  from  the  ground.  Two  depressions  like  small  wells, 

should  be  made  in  the  shelf, 
each  about  seven  inches  long, 
two  wide,  and  one  and  a  half 
deep;  they  should  be  placed 
with  one  of  their  narrowest 
ends  about  one  inch  and   a 
half  from  the  end  of  the  shelf 
which   is   furthest   from   the 
well,  and  about  eight  inches 
apart.   These  depressions  are 
to  receive  the  beaks  of  retorts 
delivering  gas  into  jars  placed  over  them ;   and  it  is  advan- 
tageous to  have  a  flap  fixed  to  this  end  of  the  trough  frame, 
which,  turned  up  or  down  at  pleasure,  may  be  used  when 
there  is  occasion  to  support  a  retort  stand  or  other  appara- 


CIRCULAR  TABLE-TROUGH SMALLER  ONES.  331 

tus  required  in  the  evolution  of  gas.  This  trough  should  be 
filled  with  water  until  it  is  one  inch  and  a  quarter,  or  one 
inch  and  a  half  above  the  shelf.  A  stop-cock  should  be  fit- 
ted into  the  bottom  of  the  well,  by  which  the  water  may 
be  drawn  off  when  it  has  become  acidified  or  dirty. 

731.  These  principal  troughs  are  sometimes  made  of  wood, 

but  never  with  advantage,  be- 
cause of  their  complexity  of  form, 
and  the  consequent  difficulty  of 
keeping  the  numerous  joints  tight. 
They  are  often  on  a  smaller  scale, 
and  when  the  chemical  establish- 
ment altogether  is  small,  are  then 
more  in  proportion  to  the  rest  of 
the  apparatus.  A  very  useful  and 
usual  table  trough  is  of  a  circular 
form,  and  about  two  feet  in  di- 
ameter, internally  divided  into  three  parts ;  the  middle  part 
is  seven  inches  deep,  and  forms  the  well,  the  other  parts  on 
each  side  four  inches  deep,  and  are  the  shelves ;  a  moveable 
shelf,  with  holes  in  it,  extends  from  side  to  side  across  the 
well,  and  serves  to  support  such  jars  as  are  receiving  gas 
from  the  beaks  of  retorts  placed  under  the  holes. 

732.  Besides  a  principal  trough,   several   smaller   ones 
are  required   for  the  preparation  of  particular  gases,  as  for 
example,  chlorine,  when  warm  water  is  required ;  or  sul- 
phuretted hydrogen,  which  contaminates  water,  and  would 
discolour  metallic  troughs.     These  may  be  either  of  metal 
or  earthenware,  and  need  not  have  fixed  shelves.     An  earth- 
enware foot-bath  makes  an  excellent  trough;  and  even  a 
washhand  basin,  or  moderately  sized  evaporating  pan,  is  at 
times  sufficiently   large,  very  portable,  and  offers    advan- 
tages. 

733.  Trivets  are  used  with  these  smaller  troughs  to  sup- 
port the  jars.     They  are  best  made  of  cast-iron,  in  the  form 
of  very  open  grates,  either  square  or  round,  and  raised  by 
means  of  three  or  four  feet ;  they  should   be  of  different 
heights,  from  half  an  inch  to  two  inches,  and  when  very  dry 
should  be  covered  with  a  good  coat  of  black  varnish,  or  made 


332  TRIVETS — CHOICE  OF  WATER  FOR  TROUGH. 

hot  almost  to  visible  redness,  and  then  brushed  over  with 
oil;  the  oil  is  in  this  way  decomposed,  and  leaves  the  metal 
covered  with  a  very  permanent  varnish.  These  trivets  an- 
swer the  purpose  of  shelves  when  required,  and  also  sup- 
port the  jars  when  filled  with  water,  so  that  the  beak  of  a 
retort,  or  the  end  of  a  tube,  may  be  introduced  beneath  them. 

734.  When  the  small  troughs  are  used,  so  much  water 
must  be  present  as  at  all  times  to  cover  the  trivets  an  inch 
or  more  in  depth.     Small  and  narrow  jars  may  be  filled  in 
them  with  water,  but  larger  jars  are  generally  filled  more 
conveniently  at  the  large    trough,  or  in  a  pail,  and  then 
transferred  in  the  manner  to  be  shortly  described   (753). 
If  during  their  use  the  water  rise   so  high  in  them  as  to  en- 
danger the  steadiness  of  the  jars  containing  gas  standing  in 
them,  a  part  must  be  removed.     The  facility  with  which  ex- 
temporaneous troughs  may  at  any  time  be  contrived,  will 
be  evident  from  what  has  been  said  relative  to  these  smaller 
arrangements. 

735.  Water  which  has  been  taken  from  a  deep  well,  from 
a  cistern  into  which  it  has  been  thrown  through  the  exertion 
of  much  power,  and  from  other  situations,  frequently  con- 
tains so  much  air  in  solution  as  to  interfere  with  the  purity 
of  gases  standing  over  it  in  the  pneumatic  trough;  for  when 
in  the  smaller  quantities  it  is  relieved  from  the  pressure  and 
other  circumstances  which  favoured  the  absorption  of  air, 
it  now    evolves  it    again    in    numerous  bubbles.      Hence 
water  which  presents  this  appearance  to  any  extent  when 
put  into  the  trough  should  be  avoided,  or  else  its  probable 
influence  should  be  remembered,  that  upon  particular  oc- 
casions it  may  not,  through  inadvertence  of  the  operator, 
introduce  inaccuracy  into  pneumatic  experiments^. 

*  In  this  country  wooden  pneumatic  cisterns  are  generally  used.  Those  of 
an  oval  shape  made  of  staves,  well  hooped,  do  not  leak  so  long  as  the  water  re- 
mains in  them. — At  the  Medical  Institute  such  a  trough  has  been  in  use  six  or 
seven  years  without  a  leak.  It  is  remarkable  that  the  author  does  not  notice  the 
great  convenience  of  having  boxes  beneath  the  pneumatic  trough  shelves  for  the 
reception  of  gases.  Gases  of  sparing  solubility  such  as  oxygen  and  hydrogen  are 
kept  conveniently  in  such  cisterns,  and  may,  by  properly  constructed  pipes  and 
stop-cocks,  be  transferred  under  the  water,  or  brought  out  above  it. — By  connec- 
ting together  two  such  gas-holders  the  pneumatic  cistern  forms  a  very  conveni- 
ent oxy-hydrogen  blow-pipe,  a  modification  of  Professor  Hare's  discovery  first 
used  by  Professor  Silliman.— ED. 


MERCURIAL    TROUGH NEWMAN'S.  333 

736.  Water  troughs  are  calculated  for  the  reception  and 
retention  of  gases  not  soluble,  or*aUerable  '4by  water,  but  not 
for  the  many  which  are  affected  by  that  fluid.     Dr  Priestly 
was  the  first  who  recommended  the  use  of  mercury;  and 
though  its  weightand  opacity  are  disadvantageous,  that  metal 
is  still  so  superior  to  any  thing  else,  as  to  be  constantly  used 
in  these  cases.  Being  expensive  as  well  as  heavy,  it  is  neces- 
sary that  the  troughs  in  which  it  is  used  should  be  as  small 
as  possible,  consistently  with  the  performance  of  experiments, 
and  at  the  same  time  of  a  material  that  will  resist  the  action 
of  the  metal.    They  have  been  made  of  wood  and  of  marble, 
but  varnished  cast-iron,  which  isnow  generally  adopted,  is  by 
far  the  best  substance.     In  principle  and  in  the  arrangement 
of  the  parts,  they  resemble  water  troughs.     Newman's  large 
mercurial  trough  will  allow  the  use  of  a  jar  two  inches  and 
two-tenths   in  diameter,  and  nine  inches  in  length ;  it  has 
seventy-six  square  inches  of  shelf  room  very  well  arranged, 
and  also  a  mercurial  gasometer  attached  to  it  at  one  extremity. 
It  requires  from  60  to  70  Ibs.  of  mercury  for  the  free  per- 
formance of  experiments. 

737.  Newman  has  also  a  much  smaller  trough  for  the  use, 

though  in  a  confined  manner,  of  jars  1.5 
inches  in  diameter,  and  six  inches  in 
length  ;  it  has  only  thirty  square  inches 
of  shelf  room.  It  requires  20  Ibs.  of 
mercury  to  fill  it,  with  a  jar  standing  on 
the  shelf.  When  working  with  jars  of 
gas  over  this  trough,  the  metal  requires  transferring  back- 
wards and  forwards,  because  of  the  difference  in  level  made 
by  the  descent  or  the  elevation  of  a  jar-full,-— but  it  is  very 
useful  in  facilitating  operations  on  small  quantities,  either 
in  tubes  or  small  jars. 

738.  A  mercurial  trough  should  always  stand  in  a  tray,  and 
likewise  have  a  cover  to  keep  out  dust  and  dirt,  when  not  in 
use.    Its  place,  as  before  described,  should  be  upon  the  table 
grooved  round  the  edge  (12),  that  waste  of  mercury  may  be 
avoided  as  much  as  possible.     When  the  metal  is  spilled  it 
is  best  collected  by  being  swept  together  and  then  gathered 


334  JARS  FOR  PNEUMATIC  TROUGHS. 

up  by  a  card.  A  card  will  even  gather  it  well  up  from  the 
surface  of  baize.  If  only  occasionally  in  use,  it  is  belter  to 
keep  the  mercury  in  stone  bottles,  than  by  constant  exposure 
in  the  trough  to  render  it  liable  to  accidents  and  loss.* 

739.  The   jars  which  accompany,  or  are  required  with, 
pneumatic  troughs,  are  of  various  kinds.     Plain  jars  should 
be  from  twelve  to  sixteen  inches  in  length,  two  and  a  half 
or  Jhree  inches  in  diameter,  of  such  thickness  (about  one- 
eighth  or  one-tenth  of  an  inch)  as  to  withstand  the  general 
liabilities  of  use,  and  ground  at  the  edges,  so  as, 
when  moistened  or  greased,  to  be  closed  accu- 
xa      rately  by  a  flat  glass  plate.     Those  for  the  mer- 
curial trough  should  be  from  four  to  eight  inches 
in  length,  one  and  a  half  or  two  inches  in  diame- 
ter, and  as  thick  as  the  former,  that  they  may 
safely  bear  their  weight  of  metal  when  filled  and 
in  use.     These  also  should  be  ground  at  the  edges. 

740.  Stoppered  jars  have  an  aperture  above,  fitted  with  a 
ground-glass  stopper,  and  resemble  stoppered  bottles  without 
bottoms.  They  are  required  of  different  sizes,  and  should  be 
larger  in  diameter  than  the  'plain  jars;  the  proportions  may 
be  gathered  from  the  figure  in  the  preceding  wood-cut. 
Such  as  are  less  than  three  inches  and  a  half  in  diameter 
should  be  ground  at  the  lower  edge,  and  all  ought  to  be 
ground  flat  at  the  top,  for  the  convenience  .of  closing  them 
occasionally  by  a  glass  plate  (1348),  instead  of  the  stopper. 
It  is  useful  in  public  laboratories,  and  often  in  private  ones, 
to  have  a  second  set  of  stoppers  for  several  of  these  jars,  the 
stoppers  having  a  projecting  knob  beneath,  to  which  a  de- 
flagrating spoon,  or  a  taper,  or  other  article,  may  be  attached 
by  a  wire.  When  it  is  required  that  any  one  of  these  should 
be  introduced  into  the  gas  already  confined  in  a  jar  by  the 

*  The  cheapest  secure  mercurial  trough  is  one  made  of  common  sheet  iron 
imbedded  in  a  wooden  box  lined  with  resinous  cement. — The  piece  of  sheet  iron 
must  be  pinched  up  at  the  corners  and  folded  so  as  to  place  all  its  edges  on  a 
level  with  the  top  of  the  box;  thus  avoiding  seams  and  the  necessity  of  any  lute 
or  solder. — The  interior  of  the  iron  trough  must  be  partly  filled  up  with  blocks 
of  close  grained  wood,  driven  in  firmly  so  as  to  form  shelves,  and  a  well,  and  occu- 
py space  which  must  otherwise  be  filled  with  mercury. — ED. 


PNEUMATIC  JARS CAPPED  FOR  TRANSFER.      335 

first  stopper,  it  is  to  be  attached  to  the  second,  and  intro- 
duced rapidly  after  the  removal  of  the  first  stopper,  and  the 
jar  closed  by  the  stopper  to  which  it  is  suspended.  When 
these  second  stoppers  are  not  at  hand,  corks  will  often  an- 
swer the  purpose  very  well,  the  wire  which  supports  the  ar- 
ticle introduced  being  thrust  through  them:  but  being  com- 
bustible, they  will  not  answer  for  deflagrations  in  oxygen  gas, 
unless  their  lower  surface  be  previously  guarded  by  a  plate 
of  sheet  lead  or  iron.  In  all  deflagrations  the  spoon  or  com- 
bustible should  for  many  reasons  be  put  as  low  down  in  the 
jar  as  possible.  A  good  cork  will  occasionally  form  a  very 
tight  and  excellent  stopper  to  an  open  jar  which  has  not 
been  ground. 

741.  The  stoppers  of  jars,  and  indeed  all  ground-glass 
stoppers,  should  be  of  considerable  thickness  where  the 
lower  and  upper  parts  are  connected  ;  for  sometimes  con- 
siderable strength  is  required  to  loosen  them  from   their 
places,  in  consequence  of  difference  of  temperature,  the 
hardening  of  some  substance  around  them,  or  other  circum- 
stances.    For  the  method  of  loosening  stoppers  thus  fixed, 
see  Sect.  xx.  (1263.)     Stoppers  should  never  be  put  into 
pneumatic  jars  without  having  been  previously  touched  by 
a  little  pomatum  or  tallow  (433),  so  as  to  make  them  fit 
easily  but  closely,  and  this  should  be  renewed  whenever 
from   use   or   cleaning   there   is  occasion  for  it.     Neither 
should  they  be  put  into  jars  or  bottles  in  a  heated  state;  the 
latter  frequently  then  contract  on  the  stoppers,  and  it  be- 
comes almost  impossible  afterwards  to  move  them. 

742.  Capped  or  transfer  jars  are  such  as,  being  open 

above,  have  a  cap  cemented  upon  them,  the 
latter  being  surmounted  by  a  stop-cock.  They 
allow  of  easy  communication  with  other  appara- 
tus, by  adopters  and  screws.  They  should  be  of 
four  or  five  different  sizes,  and  a  large  and  a 
small  one  should  be  graduated.  A  small  capped 
jar  or  two  should  be  provided  for  the  mercurial  trough,  of 
the  dimensions  before  given  (736).  These  jars  should  often 
be  examined,  to  ascertain  the  tightness  of  the  cap  and  stop- 
cock, by  which  they  are  closed.  This  is  best  done  by  nearly 


336          PNEUMATIC  JARS TUBES FUNNELS. 

filling  them  with  water  or  mercury,  according  to  the  trough 
to  which  they  belong,  without  moistening  the  stop-cocks, 
placing  them  on  a  steady  part  of  the  trough,  observing  where 
the  level  of  the  water  or  mercury  stands  within,  and  leaving 
them  for  half  an  hour  or  an  hour.  If  at  the  end  of  that  time 
the  level  be  unchanged,  the  jar  is  tight,  and  in  that  respect 
in  order. 

743.  The  lipped  glasses  before  described  (368,  505),  both 
large  and  small,  are  very  useful  as  jars  when  operations  are 
carried  on  at  the  small  troughs,  or  with  small  quantities  of 
gas ;  and  tubes  closed  at  one  end  will  frequently  be  required 
for  the  same  purposes.     These  tubes  may  be  of  any  length 
less  than  10  or  12  inches,  and  of  any  diameter ;  some  may 
be  plain,  but  several  should  be  graduated  (127)  for  the  esti- 
mation of  small  quantities  of  gas.     Those  which  are  too  wide 
to  be  closed  perfectly  by  the  finger,  should  be  ground  at  the 
edge  so  as  to  be  closed  when  required,  by  a  glass  plate 
(1348).      The    others   should    be   level,    or   nearly    so    at 
the   mouth,   and   not  irregular  from  bad  cutting   or  from 
fractures. 

744.  None  of  these  vessels  when  cracked  should  ever  be 
used  at  the  mercurial  trough;  for  they  are  not  only  rendered 
very  weak  and  are  easily  destroyed  by  a  slight  blow  near  the 
cracked  part,  but  often  suffer  the  gas  to  pass  slowly  through 
the   fissure.      They  should   rarely   be  used  at  the  water- 
trough,  except  in  very  common  experiments  ;  for,  notwith- 
standing cracks  when  moistened  are  frequently  air-tight, 
though   not  so    when  dry,  yet  they  as    often    leak,  espe- 
cially when  the  water  does  not  adhere  to  their  surface,  or 
when   the  gas  within  is  subjected  to  those  sudden  move- 
ments  which   frequently   occur    in    experiments;    besides 
these  risks,  the  jars  are  easily  broken,  and  the  gas  conse- 
quently lost. 

745.  In  addition  to  the  vessels  already  described,  small 
and  moderately-sized  funnels,  with  narrow  necks,  will  be 
required  to  assist  in  the  transference  of  gas  into  vessels  hav- 
ing narrow  apertures;  and  dishes  will  be  necessary  for  the 
removal  of  jars  containing  gas,  from  one  place  to  another. 
These  dishes  may  be  of  glass  or  earthenware,  as  evaporating 


PRODUCTION  OF  GASES GAS  BOTTLE.          337 

dishes  (369),  or  of  metal,  being  then  best  made  of  sheet 
copper,  with  a  flat  bottom  and  upright  edge.  Even  common 
soup  plates  and  tea  saucers  will  answer  the  purpose  ex- 
tremely well.  The  glass  plates  before  referred  to  (740, 
1341)  are  in  constant  use  in  closing  the  mouths  of  such  jars 
as,  not  being  too  large,  have  ground  edges. 

§  2.  Production,  retention,  and  transference  of  Gases. 

746.  The  manner  in  which  gas  is  evolved  is  very  variable. 
It  is  frequently  liberated  during  distillations  in  iron,  earthen- 
ware, or  glass  retorts  :  these  processes  have  been  described, 
and  all  that  is  now  necessary  to  be  referred  to  is  the  fact, 
that  such   apparatus  must  terminate  in  a  beak,  which  may 
either  be  directly  plunged  into  the  fluid  of  the  pneumatic 
trough,  or  lengthened   by  a  tube  which  may  have  its  extre- 
mity placed  in  a  similarsituation.  Gas  is  sometimes  produced 
by  tube  operations  (704,  718,  &c.),  and  the  manner  of  lead- 
ing it  away  by  tubes  to  the  trough  will  be  evident. 

747.  When  the  liberation  of  gas  takes  place  at  common 
temperatures  and  immediately  the  materials  are  in   contact, 
as  of  hydrogen  from   diluted  sulphuric  acid  and  zinc,  or  of 
carbonic  acid  from  muriatic  acid  and  pieces  of  marble,  then 
glass  retorts  are  sometimes  used,  and  on  other  occasions  gas 
bottles  and  flasks.     The  adaptation  of  retorts  to  these  pur- 
poses is  simple  and  evident.     Gas  bottles  are  vessels  inter- 
mediate in  their  character  between  flasks  and  bottles,  being 

thickened  at  the  neck  and  having  pieces  of 
bent  tubes  fitted  to  them  by  ground  joints ; 
the  bottle  therefore  represents  the  body  of  a 
retort,  and  the  bent  tube  the  neck.  When 
the  materials  are  introduced,  the  tube  is  put 
into  its  place,  and  its  open  extremity  im- 
mersed in  the  water  of  the  pneumatic  trough.  When  a  com- 
mon Florence  or  white  flask  has  to  perform  the  office  of  a 
generator,  it  must  have  a  piece  of  bent  tube  fitted  to  it  by  a 
good  cork  (484),  and  this  will  answer  every  purpose  required. 

748.  The  open  neck  or  tube  by  which  the  gas  is  ultimate- 
ly delivered,  whether  it  belong  to  a  retort,  a  tube  apparatus, 

2  S 


338  COLLECTION  OF  GAS — WITHOUT  LOSS. 

or  a  complicated  arrangement  of  vessels,  is  to  be  immersed 
in  the  water  of  the  pneumatic  trough.  When  the  vessel  is 
a  mere  retort  or  gas  bottle,  it  is  easily  arranged  in  a  con- 
venient situation,  being  supported  in  its  place  by  a  stand 
(380) ;  and  moveable  apparatus  of  any  kind  may  generally 
be  arranged  on  a  table  near  the  trough,  so  as  to  have  the 
necessary  juxta-position.  If  from  circumstances  the  appa- 
ratus disengaging  gas  is  fixed,  and  cannot  be  brought  to  the 
trough,  as  may  happen  for  instance  in  the  distillation  of  oxy- 
gen gas  in  an  iron  retort,  or  in  complicated  experiments  of 
research,  then  either  the  neck  must  be  prolonged  by  con- 
necting tubes  of  glass,  or  small  pneumatic  troughs  must  be 
used ;  these,  being  portable,  may  easily  be  placed  in  the 
vicinity  of  the  apparatus.  It  is  often  necessary  in  these  cases 
to  collect  large  quantities  of  gas  over  a  small  trough  ;  and 
this  is  easily  effected  by  transferring  the  jars  (753,  758)  as 
they  are  filled,  to  the  larger  trough,  and  replacing  them  by 
such  as  are  filled  with  water. 

749.  A  prime  object  in  preparing  gases  is  generally  to  col- 
lect the  pure  portions  only  ;  and  it  becomes  necessary  to  ex- 
pel the  common  air  of  the  retort  or  gas  bottle,  before  the 
particular  gas  is  collected.  For  this  reason  the  first  portions 
may  be  thrown  away  ;  but  as  a  general  rule,  it  is  better  that 
these  should  be  collected  in  a  jar,  and  then  rejected,  rather 
than,  by  leaving  the  beak  of  the  retort  exposed  to  the  air,  to 
allow  them  to  escape  at  once  into  the  atmosphere.  By  col- 
lecting them,  it  is  known  when  twice  or  thrice  the  contents 
of  the  retort  has  passed  out ;  after  that,  the  gas  may  be  col- 
lected for  use  :  by  suffering  them  to  escape  from  the  beak, 
the  estimation  of  the  quantity  rejected,  and  the  probability 
of  the  air  being  all  displaced,  is  vague  and  uncertain.  When 
a  quantity  of  gas  has  been  allowed  to  escape,  sufficient  to 
justify  the  opinion  that  what  is  afterwards  evolved  is  nearly 
or  quite  free  from  air,  the  future  portions  may  be  collected 
in  jars  for  use,  as  is  immediately  to  be  described ;  but  the 
order  of  these  jars  should  still  be  attended  to,  for  which  rea- 
son it  is  well  to  mark  them  one,  two,  three,  four,  &c.  as  they 
are  filled,  and  then,  in  case  a  portion  of  gas  perfectly  free 
from  atmospheric  air  be  required,  the  third  or  fourth  jar  may 
be  resorted  to  instead  of  the  first  or  second. 


COLLECTION    OF    GAS JARS    FILLED.  339 

750.  On  other  occasions  it  is  important  to  collect  all  the 
gas  that  may  be  evolved,  that  its  quantity  may  be  measured. 
It  is  then  frequently  necessary  to  collect  every  bubble  of  gas 
that  comes  from  the  retort,  including  the  common  air  itself. 
Then  after  having  estimated  the  whole  of  the  gaseous  pro- 
ducts, the  capacity  of  the  retort,  and  the  volume  of  solid  or 
liquid  matter  it  may  have  received  as  a  charge,  it  becomes 
easy  to  ascertain  the  volume  of  air,  and  consequently  the  vol- 
ume of  pure  gas  evolved.  In  this  case  the  jars  are  to  be 
numbered  as  they  are  filled  ;  for  though  the  first  contains 
much  atmospheric  air,  and  perhaps  also  the  second  a  little, 
the  others  are  filled  with  a  pure  gas,  which  may  be  preserved 
for  use.  The  operation  of  collecting  and  estimating  the 
whole  of  a  gas  is  delicate,  and  requires  considerable  varia- 
tion, according  to  the  nature  of  the  gas,  and  the  bodies  from 
which  it  is  to  be  evolved.  These  points  would  be  improper- 
ly introduced  into  the  description  of  elementary  operations, 
but  will  be  referred  to  again  in  a  more  advanced  part  of  the 
volume. 

751.  The  trough  being  filled  with  water  as  before  describ- 
ed (729,734),  and  the  apparatus  arranged  ready  for  the  evo- 
lution of  gas,  a  jar  is  to  be  selected,  which  we  will  consider 
for  the  present  as  a  plain  one  (739),  and  being  immersed  in 
the  water  of  the  trough  with  its  mouth  inclined  a  little  up- 
wards, so  as  to  allow  the  air  to  escape,  is  to  be  filled 
with  water.  It  is  then  to  be  raised  upright  with  its  mouth 
downwards,  and  will  be  found  to  remain  full  of  the  fluid  so 
long  as  the  mouth  is  retained  beneath  the  surface  of  the 
water;  it  may  in  that  situation  be  placed  upon  the  shelf  of 
the  trough,  or  upon  a  trivet.  If  placed  over  an  aperture  in 
the  shelf,  or  with  its  edge  projecting  a  little  way  over  the 
well,  there  will  be  no  difficulty  in  so  arranging  the  beak 
of  the  retort,  that  the  bubbles  of  gas  escaping  from  it 
shall  ascend  into  the  jar,  and,  accumulating  at  the  top, 
gradually  displace  the  water,  which  will  descend  and  mingle 
with  that  in  the  trough.  When  the  jar  is  nearly  full  of  gas, 
a  second  is  to  be  depressed  in  the  well  of  the  trough,  filled 
with  water,  and  placed  on  the  shelf  by  the  side  of  the  first: 
when  the  gas  in  the  first  is  within  half  an  inch  of  the  mouth, 


340       COLLECTION  OF  GASES — TRANSFERENCE  OF  A  JAR. 

it  is  to  be  moved  on  one  side,  the  second  put  into  its  place,  and 
filled  in  like  manner  with  gas.  Or  if  the  retort  or  ves- 
sel be  rnoveable  and  the  jars  large,  it  will  be  better  to  place 
the  second  jar  over  another  aperture,  or  projecting  conve- 
niently over  the  edge  of  the  shelf  by  the  side  of  the  first,  and 
to  transfer  the  beak  of  the  retort  from  the  first  to  the  second, 
rather  than  to  endeavour  suddenly  to  move  them:  then  after 
displacing  the  full  jar,  the  final  adjustment  of  the  retort  and 
second  jar  may  be  leisurely  made.  In  this  way  jar  is  to 
succeed  jar,  until  the  action  in  the  retort  has  ceased,  or  un- 
til sufficient  gas  has  been  collected. 

752.  The  filling  of  the  jars  with  water  in  the  well  of  the 
trough  must  be  so  conducted,  that  none  of  the  air  passing 
from  them  shall  enter  into  the  jars  already  filled  with  gas. 
For  this  reason,  when  a  jar  is  full  of  gas,  it  should  be  put 
so  far  upon  the  shelf,  that  its  mouth  may  be  entirely  closed; 
and  in  filling  the  fresh  jar  with  water,  its  mouth  is  to  be  turn- 
ed away  from  the  gas  jars  already  in  use.     The  mouth  of 
a  jar  is  not  to  be  immersed  first,  so  as  to  cause  the  air  to 
burst  forth  in  large  bubbles;  but  the  closed  end  should  be 
first  depressed,  and  the  water  suffered  to  flow  in,  and  the  air 
to  pass  out,  smoothly. 

753.  If  the  trough  in  use  be  a  small  one,  there  may  not  be 
shelf  room  in  it  for  the  jars  as  they  are  filled,  in  which  case 
it  will  be  proper  to  transfer  them  to  another  place.     For  this 
purpose  an  evaporating  or  glass  dish,  or  a  common   plate 
(744)  is  to  be  selected,  of  sufficient  size  freely  to  receive  the 
mouth  of  the  jar,  and  allow  water  to  remain  around  it;  this 
dish  is  to  be  put  into  the  water  about  an  inch  beneath  the 
surface,  and  the  jar  moved  until  its  mouth  is  received  into  it; 
this  being  done,  the  jar  and  dish  are  to  be  raised  together 
out  of  the  trough,  and  set  safely  aside.     The  water  in  the 
dish  will  confine  the  gas,  just  as  well  as  the  water  in  the 
trough,  the  dish  in  fact  becoming  a  small  trough  for  the  time; 
all  that  is  necessary  is,  to  preserve  the  portion  of  water  which 
accompanies  the  jar,  at  such  a  height  that  the  mouth  of  the 
latter  may  never  be  uncovered.     Very  little  depth  of  water  is 
required;  so  that  this  point  be  attended  to,  a  common  kitchen 
plate  will  answer  the  purpose  exceedingly  well.     The  jar  of 


COLLECTION  OF  GASES TRANSFER  JARS.  341 

gas  thus  removed  may  either  be  left  in  that  state,  or  may 
be  transferred  to  another  trough  by  immersing  the  dish  and 
mouth  of  the  jar  into  the  water  of  the  second  trough,  and 
then  removing  the  dish.* 

754.  Sometimes  also  it  will  happen,  from  the  smallness  of 
the  trough,  that  there  is  not  room  to  fill  the  jar  with  water. 
It  may  then  be  filled  in  a  pail,  or  in  the  large  trough,  and 
transferred  in  the  manner  just  described,  by   means  of  a 
plate  or  dish,  to  the  trough  at  which  the  gas  is  to  be  libera- 
ted.    The    long  jars  already  described    (739),   which  are 
ground  at  the  ends,  are  very  advantageously  transferred  by 
the  help  of  a  glass  plate   (1348):  which,   dipped  into  the 
water  and  held  tightly  against  the  mouth,  is  in  its  moistened 
state  quite  secure,  and  will  safely  retain  the  contents  of  the 
jar  during  transference,  whether  they  be  water  or  gas  or  both. 

755.  Such  is   the  manipulation  with  plain  jars  :  it  is  the 
same  with  stoppered  and  other  vessels,  except  in  occasional 
variations  in  the  mode  of  filling  them  with  water.     A  stop- 
pered jar  may  be  filled  with  water  by  removing  the  stopper, 
depressing  the  jar  in  water  in   an  upright  position  until  en- 
tirely immersed,  and  then  replacing  the  stopper  :  it  may  be 
afterwards  raised  and  used  as  a  plain  jar.     Transferring  jars, 
or  such  as,  having  a  cap  cemented  to  their  upper  aperture, 
are  finally  closed  by  a  stop-cock  (742,  827),  frequently  re- 
quire to  be  filled  with  such  care  as  to  avoid  the  introduction 
of  any  water  into   the  stop-cock.      This  may  be  done  by 
sinking  the  jar  steadily  in  water,  allowing  the  air  to  issue 
out  at  the  cock,  until   the  fluid  has  risen  into  the  cap,  and 
very  nearly  as  high  as  the  aperture  of  the  cock  itself;  then 
by  closing  the  latter  the  water  is  retained  in  the  jar. 

756.  When  there  is  not  sufficient  depth  of  water  in  the 
trough  to  admit  of  this  process,  another  method  may  be 
adopted.     It  is  to  apply  the  lips  to  the  upper  end  of  the  stop- 
cock, and  to  withdraw  the  air  by  the  force  of  the  lungs  and 
mouth.  This  may  be  done  at  one,  or  at  several  times,  a  clean 

*  Jars  thus  set  aside  are  liable  to  certain  accidents.  The  changes  of  tempera- 
ture may  eject  some  gas  or  draw  in  some  air,  evaporation  may  remove  the 
small  quantity  of  guard- water,  or  even  a  very  slight  absorption  besufficient  to  car- 
ry it  to  the  interior  oi  Ihe  jar.— Ed. 


342  TRANSFER  JARS LEVEL    OF  WATER. 

cloth  being  placed  over  the  stop-cock  to  prevent  its  contact 
with  the  lips.  As  the  water  approaches  the  cap,  its  ascent 
should  be  moderated,  and  when  within  a  very  small  distance 
of  the  cock,  it  should  be  arrested  altogether  by  closing  the 
latter. 

757.  It  is  evident  that  these  transfer  jars  cannot  be  filled 
with  water  by  inclining  them  in   the  trough,  without  intro- 
ducing the  fluid  into  the  stop-cock,  although  its  entrance 
may  be  excluded  from  the  upper  half  by  closing  it  with  the 
finger.      When  filled  with  water  they  ought  to  be  moved 
with  care,  lest  any  portion  should  be  thrown  up  into  the  stop- 
cock ;    and  when  placed  to  receive  gas,  the   first  bubbles 
should  be  admitted  with  equal  caution,  one   by  one,  or  as 
they  break  within  they  will  splash  the  liquid  into  the  aper- 
ture above.     When  the  fluid  has  descended  below  the  cap, 
so  as  to  be  in  sight,  there  is  but  little  danger  of  this  happen- 
ing, and  the  operation  may  proceed  more  rapidly.     If  pure 
gas  is  to  be  collected  in  these  jars,  it  is  necessary  that  the 
first  few  bubbles  should  be  expelled  through  the  stop-cock, 
that  they  may  carry  away  the  common  air  from  it;  this  ex- 
pulsion is  effected  by  sinking  the  jar  up  to  the  neck  in  water, 
opening  the  cock,  and  refilling  the  vessel  with  fluid.     It  can 
only  be  done  in  a  trough  or  vessel  deep  enough  to  allow  of 
sufficient  depression. 

758.  During  the  collection  of  gas  in  a  small  trough  (748), 
the  jars  being  filled  at  another  place  with  water  (754),  there 
is  of  course  a  rapid  alteration  at  the  surface  of  the  water  in 
the  trough,  from  the  continual  addition  of  that  fluid  from 
each  jar.      In  such  cases  it  is  necessary  to  lade  the  water 
out,  and  to  return  it  to  the  vessel  from  whence  it  was  taken, 
and  from  which  the  jars  were  filled.     Considerable  care  is 
sometimes  required  on  this  point,  in  order  that  the  level  of 
the  water  may  not  rise  too  far  above  the  surface  of  the  trivet 
or  shelf.     If  the  depth  of  water  be  inadvertently  allowed  to 
increase,  and  at  the  same  time  the  gas  be  permitted  to  collect 
in  the  jar  until  the  latter  is  almost  full,  it  will  frequently 
happen  that  the  jar,  becoming  buoyant,  will  fall  over  and  its 
contents  escape.     Jars,  generally,  should  not  have  the  water 


METHOD DECANTATION    OF    GAS.       343 

depressed  to  within  less  than  half  an  inch  of  their  edges,  the 
level  within  being  then  nearly  the  same  as  that  without.* 

759.  After  having  succeeded  in  collecting  gases  over  the 
trough,  the  next  facility  to  be  acquired  is  that  of  decantation 
of  them  from  one  vessel  to  another,  either  in  large  or  small 
portions,  or  with  vessels  of  different  sizes.  In  decanting  gas 
from  jar  to  jar,  which  is  the  simplest  case  of  this  kind,  the  op- 
eration is  easy,  and  in  reality  is  only  an  inverted  pouring, 
the  gas  or  air  being  poured  upwards  through  water  from  one 
vessel  to  the  other.  The  jar  into  which  the  gas  is  to  be 
introduced  is  to  be  filled  with  water,  and  placed  in  the  usual 
way  with  its  mouth  upon  the  shelf  of  the  trough,  as  if  it  were 
to  receive  the  gas  from  a  retort;  it  is  then  to  be  brought  for- 
ward over  the  well,  removing  two-thirds  or  three-fourths  of 
the  mouth  from  off  the  shelf,  so  that  though  the  jar  is  sup- 
ported by  one  edge,  another  jar  may  with  ease  be  brought 
towards  it,  and  turned  up  beneath  its  mouth.  This  done, 
and  the  jar  retained  steadily  in  the  left  hand  (that  being  usu- 
ally most  convenient  for  the  purpose),  the  second  jar  (con- 
taining the  gas  to  be  decanted),  and  which  must  previously 
have  been  placed  on  the  shelf  of  the  trough,  is  to  be  brought 
forward  by  the  right  hand,  and,  being  depressed  in  the  well, 
is  to  be  approximated  to  the  first  jar,  and  inclined  so,  that 
while  its  mouth  is  elevated  in  relation  to  the  closed  extre- 
mity, it  may  be  made  to  pass  under  the  mouth  of  the  first  jar, 
in  order  that  when  the  gas,  because  of  the  further  inclination, 
issues  out  in  bubbles  it  may  ascend  into  the  latter.  The  top 
of  the  jar  to%be  emptied  is  then  to  be  depressed  until  the 
whole  is  under  and  full  of  water,  but  this  must  be  done 
gradually  and  steadily  ;  the  gas  not  being  suffered  to  pass  out 
suddenly,  or  in  large  quantities,  for  then  the  magnitude  of 
the  bubbles  causes  them  to  interfere  in  their  ascent  with  the 
descent  of  the  water,  and  portions  are  frequently  thrown 
outside.  In  all  practice  of  this  kind,  the  experimenter  should 
endeavour  to  obtain  a  habit  of  steady  and  successful  mani- 

*  The  easy  adjustment  of  the  surface  is  often  of  importance  even  in  large  cis- 
tcins.  Dr  Hare  effects  it  by  means  of  air-vessels  near  the  bottom  of  his  trough, 
the  quantity  of  air  being  increased  or  lessened  at  pleasure,  by  peculiar  bellows. 
— Hare's  Compendium. — ED. 


344     DECANTATION  OF  GAS BY  FUNNEL — FLOATED. 

pulation  ;  and  even  when  care  may  not  be  required  for  the 
particular  experiment,  he  should  be  anxious  to  acquire  dex- 
terity, that  when  it  is  of  importance,  no  chance  of  failure 
may  be  incurred.  When  the  form  of  the  trough  is  that  de- 
scribed (729),  it  is  advantageous  to  bring  the  jar  full  of  water 
over  the  corner  of  the  well,  for  its  weight  is  then  more  safely 
supported  by  the  two  sides  of  the  shelf  above,  and  the  mouth 
of  the  jar  whose  gaseous  contents  are  to  be  transferred,  may 
more  readily  and  certainly  be  conducted  beneath  the  first 
jar,  by  means  of  the  angle  existing  in  the  well. 

760.  When  the  gas  is  to  be  transferred  from  large   into 
smaller  jars,  or  into  bottles,  more  care  is  required  than  in 
the  case  just  described.     A  jar  with  a  large  mouth  delivers 
bubbles  of  considerable  lateral  extent ;  and  when  these  rise 
towards  an  aperture,  it  is  to  be  remembered  they  cannot 
enter  it,  unless  there  be  space  for  the  passage  outwards  of 
an  equal   bulk  of  water  at  the  same  time ;  if  there  be  not, 
they  will  frequently  be  broken  and  part  of  the  gas  be  carried 
outside  and  lost.     In  these  cases  funnels  are  highly  useful, 
and  especially  in  filling  bottles  :  the  funnel,  being  inverted 
and  immersed    in   the    water,   is  to    have    its   beak  intro- 
duced into   the    mouth    of  the    bottle    filled  with    water, 
and  the  gas,  being  decanted  into  the  funnel,  is  readily  and 
safely    conducted  into    its    proper    place.     The    difficulty 
of  the  operation  is  at  first    increased,    because    attention 
is  to  be  given   to  the  funnel  and  the  bottle  at   the  same 
moment ;  for  the  former  and  the  mouth  of  the  latter  must 
both  be  retained  under  water,  and   the  edge  under  which 
the  jar  is  to  be  brought  is  necessarily  much  deeper  in  the 
trough  than  if  no  funnel  had  been  used.* 

761.  Instead  of  a  funnel,  a  lipped  jar  or  glass  (368)  may 
be  employed    in    the    transfer    as    an  intermediate  vessel. 
These,    although  they  have  wide  mouths,    deliver  narrow 
bubbles  of  air  by  the  lip,  and  to  that  owe  their  advantages. 
All  that  is  requisite  is  to  bring  the  lip  into  such  a  position 

*  Those  who  frequently  manage  gases  will  find  it  convenient  to  pass  the  neck 
of  a  light  funnel  through  a  hole  in  a  flat  cork  large  enough  to  float  the  funnel. 
The  transfer  of  gases  into  narrow-mouthed  vessels  is  thus  made  easy,  because 
the  neck  of  the  funnel  may  then  be  passed  through  a  hole  in  the  shelf  or  triv- 
et.—ED. 


TRANSFERENCE  OF  GAS BY  TUBES.  345 

that,  as  the  jar  or  glass  is  inclined,  the  lip  may  be  the  high- 
est part  of  the  mouth,  and  the  gas  consequently  tend  to  flow 
out  there. 

762.  The  manipulation  with  jars  and  glasses  is  compara- 
tively easy  to  that  which  occurs  in  transference  of  gas  from 
them  to  tubes,  or  from  tubes  to  each  other ;  and  yet  this 
latter  practice  is  continually  required  in  the  laboratory,  es- 
pecially in  eudiometrical  and  analytical  operations.     One 
circumstance  with  tubes  which  occasions  difficulty,  in  ad- 
dition to  the  narrowness  of  their  mouths,  is,  their  contracted 
capacity  within,  by  which  the  easy  passage  of  a  bubble  of 
gas  upwards,  and  water  downwards,   at  the  same  time,  is 
interfered  with ;  this  effect  is  greatest  in  tubes  of  the  smal- 
lest diameters. 

763.  No  great  difficulty  will  occur  in  the  transference 
of  gas  from  a  tube  to  another  that  is  wider.     The  second 
tube  is  to  be  filled  in  the  usual  manner  with  water,  and 

held    in   the  well   of  the  trough,    in  a 
considerably  inclined  position  ;  the  tube 
containing  the  gas  is  to  be  brought  near 
it,  the  upper  edge  of  its  mouth  inserted 
as  it  were  into  the  mouth  of  the  first,  and  then  its  posi- 
tion slowly  altered,  until  the  gas  passing  towards  the  mouth 
is  gradually  delivered  in  distinct  bubbles  into  the  first  tube. 
During  this  transfer,  the  mouth  of  the  second  tube  should 
be  retained  as  much  as  possible  within  the  first ;  the  latter 
should  not  be  raised  to  a  perpendicular  position,  but    be 
considerably  inclined,  for  then  the  edge  of  its  mouth  meets 
better  with,  and  is  adapted  to  those  of  the  second  tube,  so  as 
to  confine  the  gas,  and  the  motion  of  the  bubbles  is  less  sub- 
ject to  derangement.      Occasionally,  it  is  advantageously 
placed  in  almost  a  horizontal  position,  its  closed  extremity 
being  but  little  raised.  One  bubble  of  gas  should  be  allowed 
to  rise  to  some  height  in  the  tube  before  another  is  permitted 
to  follow. 

764.  When  the  delivering  tube  is  larger  than  the  receiv- 
ing tube,  more  care  is  required  in  the  transfer.     The  first 
tube  should  be  inclined  as  before,  and  the  upper  edge  of 
the  mouth  of  the  second  placed  within  it,  and  to  assist  in 
2  T 


346     TRANSFERENCE  OF  GAS  FROM  A  JAR  TO  A  TUBE. 

uniting  as  it  were  the  two  tubes  for  the  moment,  the  finger 
and  thumb  of  the  left  hand  (which  holds  the  receiving  tube) 
should  be  applied  at  the  sides  of  the  junction,  so  as  to  con- 
fine the  gas  and  prevent  its  escape  laterally.  For  this  pur- 
pose, and  generally  indeed  in  tube  transference,  the  tube  is 
best  held  in  the  hand,  with  its  open  extremity  passing  out 
between  the  thumb  and  fore  finger,  so  that  when  sustained 
in  the  water  in  an  inclined  position,  the  back  of  the  hand 
may  be  upwards,  the  hand  being  as  it  were  over  the  vessel; 
the  tube  is  then  easily  supported  by  the  two  or  three  last 
fingers  of  the  hand,  and  the  fore  finger  and  thumb  are  left 
at  liberty  to  guide  the  mouths  of  the  vessels,  or  to  close  the 
lateral  opening,  as  has  been  just  described.  At  other  times 
it  may  be  held  as  a  pen  is  retained  in  the  hand,  the  mouth 
being  confined  and  guided  between  the  thumb  and  two  fore 
fingers,  but  there  is  then  less  facility  in  elevating  or  de- 
pressing it  to  different  angles.  The  tubes  should  at  all 
times  be  retained  by  a  light  and  easy,  though  secure  hold, 
and  not  in  a  stiff  rigid  manner,  and  the  arms  may  often  be 
allowed  to  rest  with  advantage  on  the  edge  of  the  trough, 
whilst  the  hands  are  immersed  in  the  water. 

765.  An  intermediate  lipped  glass  should  be  used  for  the 
transference  of  gas  from  a  large  jar  to  a  tube.     No  difficulty 
will  be  found  in  transferring  from  a  lipped  glass  to  a  tube. 
The  tube  being  filled  With  water  is  to  be  held  under  the 
surface,  as  before  described  (763) ;  the  lip  is  to  be  intro- 
duced into  it,  the  junction  made  by  the  fingers  if  necessary, 
as  in  the  former  case,  and  the  gas  allowed  to  pass  in  distinct 
bubbles.     It  will  be  found  easier  to  transfer  from  a  glass 
that  is  from  a  third  to  five-sixths  full  of  gas,  than  from  one 
containing  more  or  less.     When  a  glass  is  nearly  empty, 
it  is  often  exceedingly  difficult  to  transfer  from  it  into  [a 
narrow  tube.     Advantage  may,  therefore,  occasionally  be 
taken  of  the  circumstance  above  mentioned,  by  replenishing 
the  glass  with  gas. 

766.  Finally,  small  funnels  may,  when  requisite,  be  used 
for  the  transference  of  gas  into  tubes,  the  procedure  being  ex- 
actly the  same  as  that  before  described  (760).  Tubes  contain- 
ing gases  are  easily  transferred  from  one  trough  to  another, 
or  to  other  situations,  merely  by  closing  their  mouths  with 


MEASUREMENT   OF   GASES.  347 

the  finger  or  thumb,  and  carrying  them  to  the  required  situ- 
ation. The  student  should  very  early  attain  the  habit  of 
closing  the  mouth  of  a  tube  by  the  finger  with  facility  and 
security.  The  accurate  manipulation  of  gas  in  tubes,  so 
that  none  shall  escape  and  be  lost,  is  often  essential  in 
experiments  of  research,  where  only  small  portions  of  gas 
are  evolved,  yet  require  to  be  examined  as  to  many  pro- 
perties. 

§  3.  Measurement  of  Gases. 

767.  There  are  two  cases  of  the  measurement  of  gases. 
Either  a  bulk  of  gas  is  to  be  accurately  measured,  or  the 
separation  of  a  certain  volume  from  a  larger  quantity  is  re- 
quired. The  mode  of  determining  the  bulk  of  gas  received  in 
a  plain  jar  may  be  first  considered.  The  jar  must  stand 
steadily  on  the  shelf  of  the  trough;  three  pieces  or  slips  of 
waxed  or  oiled  paper  are  then  to  be  attached  by  a  little  wax 
(1125)  and  slight  pressure,  at  equal  distances  on  the  outside 
of  the  jar,  so  that  they  may  just  adhere,  and  serve  to  mark 
the  height  of  the  water  within,  by  their  upper  edges.  The 
jar  is  then  to  be  removed  from  the  shelf  and  depressed  in 
the  well  until  the  surfaces  of  the  fluid  within  and  without 
coincide,  and  the  operator  should  observe  how  far  this 
change  of  position  has  altered  the  coincidence  of  the  three 
pieces  of  paper  with  the  surface  of  the  water  within,  taking 
care  that  the  jar  be  held  upright  during  the  observation,  so 
that  any  difference  may  be  the  same  at  each  mark.  The 
jar  should  then  be  replaced  upon  the  shelf,  and  the  situation 
of  the  paper  marks  raised  by  a  quantity  equal  to  that  which 
it  was  observed  they  were  too  low,  when  the  gas  was  levell- 
ed. This  may  easily  be  done  by  the  eye,  the  elevation  of 
the  marks  being  made  now  just  as  much  above  the  gas  with- 
in as  they  were  too  low  when  the  jar  was  depressed  in  the  well. 
The  jar  should  again  be  sunk  in  the  well  until  the  inner  and 
outer  surfaces  of  the  fluid  are  level;  the  correspondence  of  the 
marks  with  the  level  should  be  observed,  and  the  process 
carried  on  in  this  manner  until  the  adjustment  is  perfect  : 
the  papers  are  then  to  be  pressed  moreforcibly  against 
the  glass,  that  their  adhesion  may  be  secured.  The  gas 


348  MEASUREMENT  OF  GAS IN  JARS. 

is  now  to  be  transferred  (759)  into  a  graduated  jar  (742),  to 
be  depressed  also  in  the  well  until  the  inner  and  outer 
surfaces  of  the  water  being  level,  the  gas  within  may  be 
subject  only  to  the  pressure  of  the  atmosphere :  the 
graduation  is  then  to  be  observed,  and  a  direct  determina- 
tion immediately  made  of  the  quantity  of  gas  contained  in 
the  jar. 

768.  In  this  operation  the  jar  should  be  held  perfectly 
upright,  and  the  use  of  the  double  or  triple  graduation  before 
recommended  (118,  150)  will  be  evident,  from  the  facility 
with  which  it  is  now  ascertained  by  inspection,  whether  the 
jar  is  in  its  right  position,  and,  consequently,  whether  the 
determination  by  the  different  graduations  accords,  as  ought 
to  be  the  case ;  if  not,  they  may  easily  be  made  to  do  so  by 
inclining  the  jar  a  little  one  way  or  the  other,  and  the  volume 
should  not  be  considered  as  ascertained  until  both  or  all  the 
scales  agree. 

769.  In  reading  off  the  height  of  gas  in  jars,  and  also  in 
adjusting  the  paper  marks  already  referred  to,  the  observa- 
tion should  be  taken  not  from  any  part  of  the  curved  surface 
of  the  water  close  to  the  glass  (121),  but  from  the  general 
and  undisturbed  level  within;  and  when,  in  equalizing  the 
pressure  within  and  without  the  jar,  that  surface  is  necessari- 
ly brought  low  and  beneath  the  level  of  the  eye,  the  student 
should  not  be  satisfied  with  a  casual  and  oblique  glance,  but 
should  also  lower  his  eye  and  bring  it  as  nearly  as  possible 
to  a  level  with  the  surface  itself.     When  the  jar  is  thus 
lowered  in  the  well,  without  resting  any  where  upon  its  edge, 
and  sustained  only  by  the  hand,  great  assistance  and  steadi- 
ness may  be    gained  by  holding  and  pressing  it  as  it  were 
into  one  corner  of  the  well,  sustaining  it  in   part  by  friction 
against  the  sides  :  further  assistance  may  be  gained  also  by 
supporting  the  wrist  or  arm  on  the  edge  of  the  trough. 

770.  If  an  accident  happen  in  transferring  the  gas,  or  af- 
terwards in  the  graduated  jar,  before  the  volume  is  ascer- 
tained, a  record  of  the  quantity  is  preserved   by  the  three 
waxed  paper  marks  (767),  and  hence  their  great  use  :  if  no 
accident  happen,  they  still  serve  to  verify  the  measurement. 
For  the  latter  purpose  the  jar  is  to  be  removed  from  the 
trough,  set  with  its  mouth  upwards,  and  then  water  measured 


MEASUREMENT  OF  GAS READING  OFF.         349 

in  (120)  until  it  is  filled  by  that  fluid  to  the  extent  that  it  be- 
fore was  by  gas.  If  the  quantity  of  fluid  thus  introduced 
accord  with  the  measurement  of  the  gas,  an  assurance  is 
gained  of  the  accuracy  of  the  determination. 

771.  When  the  gas  is  collected  in  the  first  instance  in  a 
graduated  jar,  it  may  of  course  be  measured  in  it,  as  has  just 
been  described,  transference  being  then  avoided  ;  hence  an 
advantage,  in  many  cases,  in  receiving  gas,  requiring  to  be 
measured,  directly  in  such  jars. 

772.  If  the  gas  to  be  measured  is  contained  in  ungra- 
duated  tubes,  the  process,  though  a  little  varied,  is  the  same 
in  principle.     The  level  within  and   without  is  to  be  equal- 
ized, and  the  height  of  the  gas  marked  with:  a  file  (132),  or 
by  a  slip  of  waxed  paper  put  round  the  tube  like  a  ring.  The 
gas  is   then  to  be  transferred  into   a  graduated  tube  (734), 
levelled  (769),  and  its  volume  determined  by  the  graduation. 
Both  in  the  marking  and  observing,  particular  attention  is  to 
be  paid  to  the  curve  of  the  water,  for  the  considerations 
which  were  formerly  insisted  upon  (135),  as  important  in 
graduating,  are  now  equally  important  in  observing.     The 
practice  there  mentioned,  of  always  reading  in  the  same 
manner,  should  be  particularly  attended  to  (121),  and  by  a 
little  experience  the  point  on  the  graduation,  which  may  be 
considered  as  that  which  would  coincide  with  the  surface, 
supposing  the  gas  and  water  to  meet  by  a  plane,  may  be  as- 
certained very  accurately  from  mere  inspection.     The  tube 
in  which  the  gas  was  first  contained,  and  which  was  marked 
by  the  file  or  paper,  may  afterwards  be  measured  up  to  the 
mark  by  water  or  mercury  from  a  graduated  tube  (125,  127); 
or  if  very  small,  the  mercury  may  be  weighed,  the  precautions 
with  regard  to  convexity  of  the  surface  not  being  forgot- 
ten (135). 

773.  In  all  estimations  of  the  bulk  of  gas,  the  temper- 
ature by  the  thermometer,  and  the  pressure  as  indicated  by 
the  barometer,  should  be  observed  and  registered  in  the  la- 
boratory note  book  (1290).      No  considerable    difference 
should  be  allowed  to  exist  between  the  temperature  of  the 
air  and  water  at  the  time  of  the  experiments;  if  it  be  more 
than  a  degree  or  two,  it  should  be  corrected  by  altering  the 


350        MEASUREMENT  OF  GAS — TEMPERATURE. 

temperature  of  the  water.  The  registered  temperature 
should  be  that  of  the  water ;  and  great  care  should  be  taken 
in  handling  the  jars,  that  their  temperature  be  not  made  to 
differ  from  the  observed  one.  For  this  reason  they  should 
be  held  lightly  by  the  thick  part  of  the  neck;  and  not 
grasped  at  the  sides,  lest  a  temporary  change  of  tempera- 
ture and  consequently  of  volume  should  be  induced,  which 
in  certain  cases  might  occur  just  as  the  volume  of  the  gas 
was  under  determination.  The  barometer  should  be  an  ac- 
curate one,  or,  if  inaccurate,  the  difference  in  altitude  between 
it  and  a  perfect  instrument  should  be  known,  and  always 
allowed  for,  as  a  necessary  correction.  In  observing  this 
instrument  it  should  be  supported  perpendicularly,  the  eye 
^  being  level  with  the  surface  of  the  mercury;  it  should  be 
observed  whether  the  mercury  be  concave  or  convex,  and 
after  having  observed  its  height,  the  instrument  should  be 
slightly  tapped  to  allow  free  motion  to  the  metal,  until 
tapping  produces  no  change.  If  the  experiments  are  long, 
the  barometer  is  to  be  observed  two  or  three  times  during 
their  continuance,  that  no  unperceived  alteration  may  occur 
to  vitiate  the  results. 

774.  In  measuring  out  a  required  quantity  of  gas,  no  dif- 
ficulty will  occur  with  large  quantities.  A  graduated  jar 
is  to  be  filled  with  water,  and  the  gas  passed  into  it  (759), 
until  there  be  nearly  enough.  The  additional  portions  are 
then  to  be  added  more  carefully,  at  first  from  a  lipped  glass 
(765),  and  when  the  quantity  is  almost  sufficient,  from  a  tube. 
The  water  within  and  without  the  jar  is  to  be  brought  to  the 
same  level  at  every  examination  of  the  bulk  on  the  scale. 
Many  depressions  of  the  jar  in  the  water,  for  the  equaliza- 
tion of  pressure,  will  not  be  required,  a  facility  of  adjust- 
ment being  obtained,  by  attending  to  the  quantity  apparent- 
ly necessary  when  the  level  is  so  equalized.  Thus,  if  it  is 
found  when  the  jar  is  depressed  that  the  level  of  the  water 
within  is. one  division  higher  on  the  scale  or  graduation  than 
it  ought  to  be,  then  on  raising  it  to  the  shelf,  gas  is  to  be 
added  until  the  level  is  depressed  by  one  division,  without 
respect  to  the  particular  part  of  the  division  with  which  it 
may  happen  in  that  state  to  coincide  ;  upon  restoring  the 


MEASUREMENT  OF  GAS ADJUSTMENT.         351 

• 

equality  of  level,  the  quantity  will  be  found  very  nearly  ac- 
curate, and  the  portion  that  is  necessary  to  make  it  quite  so, 
may  now  very  well  be  estimated,  and  accurately  added  at 
the  next  trial. 

775.  The  advantage  of  using  the  tube  for  the  addition  of 
the  last  portions  is,  that  much  smaller  bubbles  may  be  de- 
livered into  the  jar,  and  the  final  adjustment  be  more  accu- 
rately made.    If  the  aperture  of  a  tube  at  the  trough  contain- 
ing gas  be  closed  by  the  fore  finger  (of  the  right  hand), 
whilst  it  is  held  by  the  thumb  and  other  fingers,  and  inclined 
under  the  water,  with  the  mouth  upwards,  so  that  the  gas 
within  would  escape  but  for  the  finger,  then  if  the  finger  be 
relaxed  a  very  little  at  the  lower  edge,  so  that  a  small  quan- 
tity of  water  may  flow  in,  and  the  mouth  be  immediately 
closed  as  before,  it  will  be  found,  that  at  each  operation  a 
bubble  of  air  will  be  expelled  from  the  tube,  the  dimension 
of  which  will  depend  on  the  degree  in  which  the  finger  was 
withdrawn,  and  on  the  quantity  of  water  consequently  ad- 
mitted.    In  this  manner  bubbles  smaller  than  a  pin's  head 
may  be  obtained,  and  consequently  a  very  minute  quantity  of 
gas  may  be  added,  whereas  risk  of  adding  too  much  in  one 
large  bubble  is  incurred,  if  the  gas  be  let  out  from  a  tube 
not  thus  guarded  by  the  finger,  or  from  a  glass  or  jar.* 

776.  In  measuring  quantities  in  tubes,  for  eudiometrical 
and  other  experiments,  more  care  is  required  than  is  usually 
necessary  with  large  quantities,  because  general  proportions 
and  results  are  frequently  deduced  from  very  small  volumes. 
In  these  cases  standard  or  unit  measures  are  often  useful,  and 
being   equally  filled  again   and  again,    afford   a  series   of 
equal  volumes.     In  filling  them,  however,  it  is  not  sufficient 
that  gas  be  passed  into  them  until  they  overflow,  for  from 
the  cohesion  of  the  water,  and  other  circumstances,  this 
will  take  place  when  the  measure  contains  very  different 
quantities,  and  it  will  in  almost  all  cases  be  rather  more  than 
full,   the   gas   projecting    beyond   the  edge   of   the  tube. 
When  therefore  such  measures  are  made  out  of  tubes  ( 142), 

*  For  the  transfer  of  minute  portions  of  gas  the  most  elegant  instrument  is 
Dr  Hare's  sliding- rod  gas-measure,  which  also  accurately  determines  the  quan- 
tity.—ED. 


352         MEASUREMENT  OF  GAS CAVENDISH'S  MEASURE. 

it  is  usual  to  close  them  when  full  of  gas  by  the  finger,  the 
excess  being  thus  thrown  off;  but,  inasmuch  as  the  skin 
when  dry  or  soaked,  or  when  slightly  or  forcibly  pressed, 
enters  more  or  less  into  the  opening  of  the  tube,  an  inac- 
curacy is  occasioned  unless  the  operator  be  careful  always 
to  make  the  applied  part  of  the  finger  assume  the  same  con- 
vexity, and  the  measure  used  be  of  small  diameter.  With 
these  precautions  this  is  a  very  good  mode  of  measuring. 
These  tubes  are  sometimes  closed  by  stoppers  so  adjusted, 
as  to  leave  a  capacity  of  the  proper  measurement,  and  oc- 
casionally larger  measures,  amounting  to  the  half  or  the 
whole  of  a  cubic  inch,  are  made  of  bottles  carefully  stopped 
and  adjusted  for  the  purpose  (125). 

777.  In  using  measures  of  this  sort  a  surplus  of  gas  is  to 
be  introduced,  the  stopper  put  into  its  place,  and  the  excess 
thrown  out  ;  but  in  introducing  the  stopper  it  must  be  done 
in  such  a  manner  as  to  exclude  water  as  much  as  possible 
from  the  measure.  It  should  be  introduced  at  first  obliquely, 
one  edge  being  a  little  higher  than  the  other,  whilst  the  mea- 
sure itself  is  quite  perpendicular.  It  should  be  observed 
that  the  gas  descends  on  all  sides  of  the  stopper,  or  at  least 
that  no  large  quantity  of  water  is  carried  up  on  one  side ; 
and  this  being  the  case  it  may  be  thrust  into  its  place,  the 
extra  bubble  of  gas  thrown  off,  and  that  within  the  measure 
used  as  required.  If  the  measure  be  inclined,  and  the  stop- 
per put  in  carelessly,  it  will  be  found  in  most  instances  that 
a  quantity  of  water  has  been  carried  up  into  the  bottle  or 
measure,  on  the  bottom  of  the  stopper,  notwithstanding  the 
considerable  excess  of  gas  that  was  first  introduced. 

778.  Mr  Cavendish  used  a  measure  for  these  purposes, 
consisting  of  apiece  of  glass  tube  closed  at 
one  end  and  fitted  into  a  brass  collar,  with  a 
flat  slider  passing  through  it  -,  this,  when 
thrust  forwards  in  a  direction  at  right  angles 
to  that  of  the  tube,  closed  its  mouth,  and  included  a  space 
accurately  adjusted  to  half  a  cubic  inch.  When  used,  the 
slider  was  opened,  and  a  surplus  of  gas  passed  into  the  tube, 
the  slider  was  then  closed,  the  excess  of  gas  beneath  it  thrown 


MEASUREMENT  OF  GAS — MEASURES.  353 

away,  and  the  included  and  accurately  measured  volume  re- 
tained for  use. 

779.  When  in  consequence  of  the  nature  of  the  experiment 
and  of  the  measure  used,  the  operation  does  not  consist  in 
accurately  filling  a  measure  or  tube,  but  in  filling  it  to  a  cer- 
tain mark  only,  as  for  instance,  to  the  fifth  or  tenth  division 
on  the  graduation     and  in  general  this  will  be  the  kind  of 
measurement  required  in  tubes),  a  little  excess  of  gas  above 
what  is  wanted  should  be  put  into  the  tube,  and  the  adjust- 
ment effected  by  closing  the  mouth  with  the  finger,  and  let- 
ting out  minute  bubbles  in  the  manner  just  described  (775). 
The  tube  is  to.be  returned  to  an  upright  position  occasion- 
ally, and  the  quantity  left  examined  as  to  its  accordance  with 
the  graduation  in  the  required  place.     If  by  accident  too 
much  gas  has  been  thrown  out,  a  little  more  must  be  added, 
and  the  adjustment  proceeded  with  as  before.     If  the  gas  be 
valuable  or  in  minute  quantity,  then  the  small  bubbles  ejected 
should  not  be  thrown  away,  but  caught  in  a  little  tube  held 
over  them,  and  reserved  for  other  experiments.  A  very  quick 
and  accurate  adjustment  of  a  required  quantity  of  gas  may 
in  this  way  be  obtained. 

780.  In  observing  the  volume  of  gas  in  a  tube,  after  hav- 
ing brought  the  internal  and  external  surfaces  of  water  to  a 
level,  the  necessity  of  lowering  the  eye  to  the  level  of  the 
water  may  be  avoided  by  closing  the  mouth  of  the  tube  with 
the  finger,  and  then  raising  it  out  of  the  water  to  the  height 
of  the  eye  ;  but  the  act  of  closing  the  tube  must  be  so  per- 
formed, that  the  pressure  of  the  finger  does  not  compress  the 
gas  within,  and  raise  the  level  above  its  proper  place.     If 
the  finger  be   applied  to  all  parts  of  the  edge  at  once,  and 
then  pressed  hard,  this  effect  will  almost  certainly  take  place. 
To  avoid  it,  the  finger  should  not  be  applied  directly  against 
the  mouth  of  the  tube,  but  a  little  obliquely,  pressing  it  hard 
against  the  part  of  the  edge  it  first  meets,  and  then  folding 
it  over,  so  as  to  cover  the  mouth  gradually  from  one  side  to 
the  other  :  the  pressure  at  last  upon  the  whole  edge  being 
less  than  that  with  which  the  operation  began.     In  this  man- 
ner the  tube  may  be  closed  without  any  change  of  level,  and 
it  should  be  observed  during  the  operation,  that  this  is  the 

2U 


354         GAS  COLLECTED MERCURIAL  TROUGH. 

case.  When  the  habit  is  once  attained  the  practice  is  quick, 
and  in  long  sets  of  pneumatic  experiments  the  operator  is 
enabled  by  it  to  avoid  some  degree  of  fatigue. 

781.  The  barometer  and  thermometer  should  be  attended 
to  in  all  these  experiments,  unless  the  latter  are  brief,  or  are 
such  as  to  require  merely  relative  portions  of  two  gases,  their 
absolute  quantities  being  unimportant. 

782.  The  operations  which  have  been  described  have  all 
been  illustrated  by  reference  to  the  water  trough,  and  to 
gases  permanent  over  it.     They  are  the  same  in  principle  as 
those  which  will  be  necessary  in  experiments  at  the  mercurial 
trough  (736),  with  those  gases  which,  being  soluble  in  water, 
cannot  be  preserved  over  that  fluid.     The  first  point  the 
student  has  to  remember  at  the  mercurial  trough  is,  the  ex- 
cessive weight  of  the  fluid  with  which  he  is  working,  and  its 
influence  in  his  operations,  either  as  coinciding  with  or  op- 
posing the  pressure  of  the  atmosphere.     If  the  extremity  of 
a  retort,  or  the  mouth  of  an  apparatus,  delivering  gas,  be  im- 
mersed,  for  example,  an  inch,  in   the   water  trough,  and 
another  to  the  same  depth  in  a  mercurial  trough,  the  pressure 
upon  the  interior  of  the  apparatus,  which  is  so  little  as  to  be 
unimportant  in  the  first  case,  becomes  of  consequence  in  the 
second,  being  nearly  fourteen  times  greater.    The  latter,  if 
unattended  to,  might  derange  and  burst  open  joints  made  by. 
soft  cement  or  lute;  might  force  the  evolved  gases  through 
bladder  or  junctions  quite  tight  to  the  pressure  of  water;  and 
might  blow  out  a  tube  or  retort  heated  to  redness,  as  in  the 
preparation  of  oxygen  gas  from  the  chlorate  of  potash,  which 
would  have  suffered  little  or  no  change  at  the  water  trough. 
Hence  the  beak  of  such  apparatus  should  be  immersed  to 
no  greater  depth  in  the  mercury  than  is  necessary  to  insure 
the  safe  delivery  of  the  gas  into  the  jar  placed  to  receive  it. 
Hence  also  the  shelf  of  the  trough  should  not  be  covered 
with  mercury  to  a  greater  depth  than  is  necessary  to^ecure 
the  mouths  of  vessels  placed  upon  it;  and  jars,  if  supported  by 
other  means,  as  by  trivets  or  stands,  in  small  or  temporary 
troughs,  should  be  so  arranged  that  their  mouths  may  not  be 
too  far  below  the  surface  whilst  receiving  gas. 

783.  The  mercurial  jars  are,  as  before  described  (739),  to 


MERCURIAL  TROUGH — JARS  FILLED.  355 

be  strong,  and  ground  at  the  edges.  If  they  are  lipped, 
which  is  very  desirable  in  many  cases  for  the  advantage  of 
transferring,  the  lip  should  be  level  with  the  rest  of  the  edge, 
so  as  to  bear  upon  a  flat  surface  at  the  same  time  with  the 
other  parts;*  and  not,  as  is  usually  the  case,  retiring  out- 
wards towards  the  bottom  of  the  jar,  so  as  to  leave  a  space 
between  the  lip  and  a  glass  plate  applied  to  the  mouth.  The 
jars  maybe  filled,  either  by  inverting  them  in  the  mercury  of 
the  trough  itself  (751),  or  with  mercury  from  another  vessel; 
in  the  latter  case  the  mouth  is  to  be  closed  by  a  glass  plate 
(1348),  the  jar  afterwards  inverted,  and  its  mouth  immersed 
in  the  metal  of  the  trough,  and  the  plate  withdrawn.  But 
when  jars  containing  mercury  are  thus  closed  either  for  the 
purpose  described  or  the  transference  of  gas,  a  strong  hold 
on  the  plate  must  be  retained,  to  prevent  its  displacement 
by  the  weight  of  metal  upon  it. 

784.  In  moving  ajar  partly  or  entirely  filled  with  mercury, 
from  one  part  of  the  trough  to  another,  great  care  should  be 
taken  to  prevent  its  receiving  any  sudden  blow  or  jerk,  for 
though  slight  in  appearance,  it  might,  from  the  weight  of  the 
mass  moved,  suffice  to  break  the  jar;  upon  such  occasions  the 
whole  weight  of  mercury  suddenly  descends,  .sometimes  de- 
ranging every  thing  in  the  trough,  besides  occasioning  the 
loss  of  the  metal  and  the  escape  of  the  gas.     The  jars  are 
under  these  circumstances,  most  liable  to  injury   by  slight 
blows  against  each  other,  or  against  the  iron  of  the  trough, 
when  they  take  place  upon  the  edges  or  sides. 

785.  When  a  mercurial  jar  contains   gas  it  may  be   re- 
moved from  the.  trough,  as  already  mentioned  (739,783), 
by  a  glass  plate;  but  if  it  contain  a  considerable  quantity  of 
mercury,  it  is  safer  to  effect  the  transfer  by  a  little  evapora- 
ting basin  (745,  753.) 

786.  When  a  capped  jar  is  to  be  filled  with  mercury,  by 
the  assistance  of  the  mouth  (756),  the  jar  should  be  inclined 
as  much  as  possible,  to  diminish  the   height  of  the  column 
of  air  within  it,  as  well  as  the  labour  attending  the  opera- 
tion; then  by  applying  the  mouth  to  the  stop-cock,  and  using 
it  to  exhaust,  in  a  manner  almost  the  reverse  of  that  describ- 
ed for  blow-pipe  practice  (222,  &c.),  the  air  may  be  with- 


356        MERCURIAL  TROUGH — GAS  TRANSFERRED. 

drawn,  and  the  mercury  gradually  raised  until  it  fills  the 
jar.  Relief  should  be  afforded  to  the  mouth  by  closing 
the  stop-cock  occasionally  during  the  operation;  the  cloth 
should  generally  be  applied  over  the  aperture  (756),  and  no 
moisture  should  be  allowed  to  enter  the  stop-cock.* 

787.  The  transference  of  gas  from  vessel  to  vessel  under 
mercury,  is  the  same  in  principle  with  transference   under 
water,  but  differs  from  it  in  consequence  of  the  opacity  and 
weight  of  the  fluid;  the  first  of  which  prevents  the  experi- 
menter from  watching  the  motion  of  the  gas,  and  obliges  him 
to  work  in  the  dark,  whilst  the  second  causes  the  bubbles 
which  leave  the  decanting  jar  to  be  thrown  up  through  the 
fluid  with  considerable  force.     Great  care  is  therefore  required 
in  these  operations,  and  especially  with  tubes.     The  relative 
and  desired  position  of  the  mouths  of  the  vessels  must  be 
judged  of  principally  by  feeling  with  the  fingers.     The  de- 
pression of  the  decanting  tube  should  be  very  slow  and  gra- 
dual.    The  escape  of  the  first  bubble  should  be  watched;  if  it 
ascends  into  the  receiving  tube,  all  is  well,  and  the  position  of 
the  mouths  should  be  steadily  retained;  but  if  it  escape  into 
the  air,  the  position  should  be  changed .     Generally  speaking, 
the  mouth  of  the  decanting  vessel  ought  to  be  farther  under 
the  mouth  of  the  receiving  vessel  than  is  required  in  water. 
When  tubes  are  the  vessels  employed,  the  use  of  the  fingers  in 
closing  the  sides  (764)  is  often  highly  advantageous. 

788.  There  is  one  circumstance  in  which  water  and  mer- 
curial troughs  essentially  differ,  and  of  which  the  student 
should  be  fully  aware,  as  it  will  account  to  him  for  many  acci- 
dents that  otherwise  might  occur  at  the  commencement  of  his 
experience,  in  the  transferring  and  collecting  of  gases,  and  en- 
able him  in  most  cases  to  avoid  them.     This  consists  in  the 
property  which  water  has  of  wetting  and  adhering  to  the  sur- 
faces of  the  jars  and  apparatus  concerned  in  operations  at  the 
pneumatic  trough,  which  is  not  possessed  by  mercury.     Hence 
it  is  that  portions  of  gas,  expelled  from  apertures  under  water, 
rise  in  distinct  bubbles  through  the  fluid  about  them;  for  the 

*  The  best  mode  of  arresting  the  influx  of  saliva  or  moisture  is  the  placing  a 
piece  of  well  dried  sponge  in  the  mouth  of  the  stop-cock.— ED. 


ESCAPE  OF  GAS  IN  MERCURIAL  TROUGH.        357 

adhesion  of  the  water  to  the  solid  substances  generally  in  use 
is  greater  than  that  existing  between  its  own  particles.  It  is 
not  so,  however,  with  mercury;  that  metal  does  not  <;ome  into 
such  close  contact  with  glass  or  other  substances  as  to  adhere, 
and  hence  it  often  happens  t'hat  the  gas  ejected  from  the 
aperture,  instead  of  being  thrown  as  a  bubble  into  the  fluid 
metal,  suddenly  returns  round  the  edge,  and  passes  up  in  a 
stream  between  the  vessel  and  the  mercury.  It  is  in  this 
way  diffused  for  a  moment  in  thin  filnrft  over  a  large  surface, 
and  ultimately  escapes  at  the  ring,  where  the  surface  of  the 
mercury  ought  to  be  in  contact  with  the  vessel  from  which 
the  gas  is  thrown  out.  The  collection  or  retention  of  the  gas 
in  such  cases  is  utterly  impossible,  its  passage  in  the  form  of 
bubbles  being  necessary  for  that  purpose. 

789.  This  insidious  emission  of  gas  takes  place  with  little 
or  no  disturbance  of  the  mercury,  and  is  sometimes  quite 
imperceptible.     It  can  only  occur  when  the  vessel  delivering 
the  gas  proceeds  from  above  downwards,  in  the  manner  of  a 
jar,  or  the  beak  of  a  retort,  or  a  descending  straight  tube,  so 
that  when  the  extremity  of  a  tube  is  curved,  and  made  to  turn 
up  under  the  surface  of  the  mercury,  it  is  avoided.     It  is 
very  usual  with  dirty  vessels,  and   may  often  be  prevented 
by  wiping  them  clean:  this  is  especially  the  case  with  the 
beaks  of  retorts  delivering  gas.     It  is  more  likely  to  occur  in 
dirty  than  in  clean  mercury  (1278).     In  such  cases,  though 
it  may  not  take  place  immediately,  it  frequently  will  after 
the  lapse  of  a  short  time,  the  agitation  of  the  mercury  appa- 
rently collecting  a  film,  or  diminishing  the  adhesion  between 
the  metal  and  the  glass.     Wiping  the  glass  with  a  clean 
cloth,  even  whilst  under  the  metal,  is  then  a  remedy. 

790.  Some  gases  have  a  tendency  to  occasion  this  effect 
more  than  others,  and  amongst  them  may  be  quoted  fluoboric 
and  silicated  fluoric  acid  gases,  and  euchlorine.    The  necks  of 
retorts  delivering  these  gases  should  be  wiped  occasionally. 
The  effect  happens  more  readily  when  the  sides  of  the*  vessel 
or  delivering  tube  approach  to  perpendicularity,  than  when 
they  are  much  inclined,  so  as  to  approximate  to  a  horizontal 
position;  and  finally,  it  often  occurs  between  the  fingers  and 
the  mercury,  the  transpired  matter  on  the  surface  of  the  skin 
apparently  facilitating  the  effect.     Hence  when  the  fingers 


358    TRANSFERRING  A  GAS  FROM  WATER  TO  MERCURY. 

are  brought  into  contact  with  the  gas  in  transferring  ope- 
rations, they  should,  when  the  effect  is  likely  to  occur,  be 
bent  upwards  under  the  mercury  as  much  as  possible. 

791.  It  frequently  happens  that  small  quantities  of  gas 
are  to  be  taken  from  larger  portions  and  transferred  to  other 
situations.     This  is  constantly  the  case  in  analytical  and 
eudiometrical  experiments,  where  small  volumes  are  requir- 
ed in  tubes  or  narrow  vessels.     Another  common  case  is  the 
transference  of  a  smart  portion  of  gas  from  a  jar  over  water 
into  a  vessel  over  mercury,  the  transmission  of  water  at  the 
same  time  being  avoided.     As  these  operations  are  frequent, 
several  useful  contrivances  have  been  invented  to  facilitate 
them. 

792.  A  common  method  of  transferring  a  little  gas  from 
the  water  to  the  mercurial  trough  in  the  dry  state  is,  to  fill 
a  tube  with  the  gas  over  water,  to  close  it  by  the  finger, 
then  removing  it  from  the  trough,  to  wipe  the  outside  of  the 
tube  and  hand  dry,  taking  care  that  the  gas  be  securely  re- 
tained during  the  operation.     The  tube  is  afterwards  to  be 
carried  to  the  mercurial  trough,  the  finger  to  be  removed, 
and  a  little  piece  of  bibulous  paper,  tightly  rolled  up,  intro- 
duced through  the  mercury  into  the  gas.     By  re-applying 
the  finger  so  as  to  close  the  tube,  and  shaking  the  piece  of 
paper  about  within,  it  imbibes  a  large  portion  of  the  water, 
and  the  gas  may  afterwards  be  decanted  into  another  tube 
filled  with  mercury,  without  any  risk  of  water  passing  with 
it,  for  the  fluid  will  be  retained  by  the  paper  or  by  adhesion 
to  the  glass.    The  gas  is  thus  obtained  in  a  dry  state,  or  at 
least  without  the  presence  of  any  fluid  water.     With  regard 
to  its  hygrometric  state,  it,  of  course,  still  remains  saturated 
with  aqueous  vapour. 

f  793.  A  very  useful  contrivance  for  the  same  purpose,  due 
to  Mr  Cavendish,  is  thus  described  by  Dr  Henry*.  "  A 
tube  eight  or  ten  inches  long,  and  of  a  very  small  diameter, 
is  drawn  out  to  a  fine  bore,  and  bent  at  the  end  so  as  to  re- 
semble the  italic  letter  I.  The  point  is  then  immersed  in 
quicksilver,  which  is  drawn  into  the  tube  till  it  is  filled,  by 
the  action  of  the  mouth.  Placing  the  finger  over  the  aper- 

*  Elements  of  Experimental  Chemistry,  i:  22. 


INSTRUMENTS  OF  TRANSFERENCE. 


359 


ture  at  the  straight  end,  the  tube  filled  with  quicksilver  is 
next  conveyed  through  the  water  with  the  bent  end  upper- 
most, into  an  inverted  jar  of  gas.  When  the  finger  is  re- 
moved, the  quicksilver  falls  from  the  tube  into  the  trough,  or 
into  a  cup  placed  to  receive  it,  and  the  tube  is  filled  with 
the  gas.  The  whole  of  the  quicksilver,  however,  must  not  be 
allowed  to  escape,  but  a  column  must  be  left  a  few  inches 
long,  and  kept  in  its  place  by  the  finger.  The  tube  is  to  be 
removed  from  the  water,  and  dried  by  an  assistant  with  a 
towel  or  with  blotting  paper;  the  point  of  the  bent  tube  is 
then  to  be  introduced  into  the  aperture  of  the  tube 
standing  over  quicksilver,  and  on  withdrawing  the  finger 
from  the  aperture,  which  is  now  uppermost,  the  pressure 
of  the  column  of  quicksilver,  added  to  the  weight  of  the 
atmosphere,  will  force  the  gas  from  the  bent  tube  into  tke 
one  standing  in  the  mercurial  trough."  * 

794.  Mr  Pepys  has  invented  a  very  useful  instrument  for 
the  transference  of  small  quantities  of  gas  from  one  vessel  to 
(Q  another  over  the  trough,  which  he  permits 
me  to  describe.  It  is  made  of  a  piece  of 
glass  tube,  about  half  an  inch  in  diameter, 
and  five  inches  long,  attached  to  a  piece  of 
smaller  diameter,  which,  after  bending  as  in 
the  figure,  terminates  in  a  chamber  at  a, 
which,  being  cylindrical  for  the  greater 
part  of  its  length,  terminates  in  a  capillary 
tube  and  aperture.  A  small  piston, 
rendered  air-tight  by  tow  and  tallow,  is  fitted  into  the  cy- 
lindrical tube  ;  it  is  moved  by  a  rod  and  ring,  the  rod  pass- 
ing through  a  box  which  closes  the  upper  aperture  of  the 
instrument,  but  which  should  not  be  air-tight.  A  portion  of 
mercury  is  placed  above  the  piston,  and  the  space  between? 
it  and  the  capillary  opening  of  the  chamber  is  filled  with 
the  same  metal  when  the  piston  is  in  the  position  depicted. 
Upon  raising  the  piston,  the  mercury  follows  it,  and  de- 
scends into  the  chamber  a,  the  space  left  by  it  being  imme- 
diately filled  with  the  air  or  gas  which  has  access  to  the  ca- 


360  TRANSFERRER  USED. 

pillary  opening.  The  rod  has  a  graduation  upon  it,  by 
which  it  is  known  when  a  tenth  of  a  cubical  inch  of  air  has 
entered  the  chamber.* 

795.  The  following  is  the  mode  of  using  this  instrument. 
Suppose  the  object  be  to  transfer  a  little  gas  from  a  jar  to  a 
eudiometer  tube,  both    standing   over    the    same    trough : 
the  piston  is  to  be  depressed  until  the  mercury  entirely  fills 
the  chamber  a,  even  up  to  the  aperture;  that  end  is  to  be 
dipped  into  the  mercury  in  the  trough,  and  passed  under  the 
edge  of  the  jar  containing  the  gas;  it  is  then  to  be  raised 
above  the  surface  of  the  mercury  within,  and  the  piston  lift- 
ed :  this  will  cause  the  descent  of  the  mercury  in  the  cham- 
ber a  within  the  jar,  which  consequently  will  be  replaced  by 
the  gas  surrounding  it.     As  soon  as  enough  has  entered,  the 
iHotion  of  the  piston  is  to  be  suspended,  the  aperture  of  the 
instrument  depressed  into  the  mercury,  the  piston  raised  a 
very  little  for  the  purpose  of  drawing  a  globule  of  mercury 
into  the  capillary  part,  the  chamber  a  again  elevated  into 
the  jar  to  ascertain  that  this  has  been  done.,  and  then  the  in- 
strument removed  through  the  mercury  away  from  the  jar. 
The  portion  of  gas  within  it  will  be  confined  both  above  and 
below  by  the  metal,  and  when  it  is  to  be  transferred  to  the 
eudiometer  tube,  all  that  is  necessary  kis,  to  introduce  the  ca- 
pillary%)ening  into  the  mouth  of  the  tube,  and  to  depress 
the  piston.     The  gas  is  immediately  ejected  from  the  cham- 
ber, and  in  £  manner  so  much  tinder  command,  that  it  is 
easy  to  throw  up  just  that  quantity  which,  by  the  graduation 
on  the  eudiometer  tube,  or  on  the  stem  of  the  instrument,  is 
known  to  be  required  for  the  experiment.     When  measuring 
by  the  graduation  on  the  instrument  itself,  it  is  necessary 
to  bring  the  fevel  within  and  without  the  jar  from  which  the 
gas  is  taken,  to  the  same  height,  or  else  the  gas  measured 
will  not  possess  the  same  volume  at  common  pressure. 

796.  The  same  instrument  is  equally  useful  in  removing 
portions  of  gas  from  a  jar  over  water,  and  conveying  them, 

*  From  the  construction  of  the  piston,  it  is  apparent  that  this  instrument  is  a 
* etrogradation  from  that  of  Dr  Hare's  invention,  which  long  preceded  it,— EB. 


361 

in  a  dry  state,  to  a  jar  or  tube  over  mercury.  Being  full  of 
mercury,  it  is  to  be  introduced  into  the  jar  as  before;  water 
rarely  adheres  in  any  quantity  to  the  summit  of  the  capillary 
termination,  or  if  a  drop  should,  a  slight  lateral  shake  throws 
it  off.  By  raising  the  piston,  the  mercury  in  the  chamber 
falls  and  the  gas  enters;  to  confine  it  there,  the  instrument 
should  receive  a  cautious  jerk,  so  as  to  throw  the  mercury 
up  towards  the  capillary  opening;  it  will  be  found  easy  to 
make  a  globule  adhere  there,  and  when  that  is  the  case,  by 
depressing  the  piston,  to  cause  it  to  enter  into  the  capillary 
part  so  as  to  close  it  perfectly.  The  instrument  is  then  to 
be  removed  from  the  jar  and  water,  wiped  dry,  and  the  gas 
conveyed  into  the  required  vessel,  as  before. 

797.  The  instrument,  described  and  figured  (151),  is  used 
by  Dr  Hare  in  transferring  accurately  measured  portions  of 
gas  from  one  vessel  to  another  over  mercury.     Its  use  is  easy, 
and  will  be  understood  from  the  description  given  of  the  in- 
strument.    When  full  of  mercury,  the  beak  is  introduced 
under  the  edge  of  the  jar  into  the  gas  above,  and  by  with- 
drawing the  rod  a  certain  number  of  degrees,  an  equal  vol- 
ume of  the  gas  enters,  and  is  easily  transferred  to  any  other 
vessel  at  pleasure. 

798.  The  general  processes  for  measuring  gas  over  mercury, 
are  the  same  with  those  already  directed  for  similar  opera- 
tions over  water  (767);  the  propriety  of  marking  the  jar  or 
tube,  before  any  attempt  to  estimate  the  volume,  is  even 
greater  here  than  on  the  former  occasion,  because  of  the 
greater  risk  of  the  gas  escaping  in  transference,  or  of  the 
occurrence  of  other  accidents.     When  regulating  the  quan- 
tity in  a  tube  (775),  the  finger  is  not  of  the  service  in  this 
as  in  the  former  case,  for  the  reasons  already  stated  (788, 
789);  but  to  make  the  utmost  use  possible  of  it,  with  the 
least  risk  of  accidental  escape  of  the  gas,  it  should  be  held 
in  a  bent  position  under  the  mercury,  rising  upwards  to  the 
extremity  and  not  from  it,  that  the  chances  of  escape  of  the 
gas  may  be  diminished  (789).     It  is  in  cases  where  these 
difficulties  with  gas  over  mercury  occur,  that  the  instruments 
just  described  are  particularly  useful. 

2  V 


362  MEASUREMENT  OF  GAS  OVER  MERCURY. 

799.  When  the  gas  to  be  measured  is  in  a  tube,  the  ad- 
vantage of  the  process  (767,772),  in  which  the  height  is 
marked,  the  gas  transferred  and  thrown  away,  and  its  volume 
ascertained  by  the  weight  of  mercury  replacing  it  (126,131), 
is  much  greater  over  the  mercurial  than  over  the  water  trough, 
simply  because  it  dispenses  with   the  somewhat  uncertain 
operation  of  transferring  the  gas  under  mercury.     But  the 
experimenter  must  then  remember  the  cautions  already  given, 
with  regard  to  the  opposite  convexities  of  the  mercury,  when 
it  is  at  first  confining  the  gas  and  afterwards  replacing  it 
(135);  and  besides  marking  the  true  bulk  with  care,  he 
should  be  equally  careful  in  estimating  the  quantity  of  mer- 
cury which  is  to  replace  it. 

800.  In  all  measurements  and  estimations  of  gas  over 
mercury,  particular  attention  should.be  given  to  bring  the  me- 
tal inside  and  outside  the  vessel  to  the  same  level;  or  if  there 
be  not  sufficient  depth  of  mercury  for  the  purpose,  the  height 
of  the  surface  in  the  jar  or  tube  above  that  in  the  trough 
should  be  accurately  measured  and  noted  down.     This  be- 
comes a  deduction  necessary  to  be  made  from  the  observed 
height  of  the  barometer,  when  the  volume  of  the  gas  is  to  be 
corrected,  and  its  true  bulk  at   mean  temperature  and   pres- 
sure ascertained  (883). 

801.  In  experiments  requiring  the  use  of  a  large  jar  at  the 
mercurial  trough,  it  is  frequently  desirable  to  possess  the 
means  of  raising  or  lowering  the  surface  of  the  mercury  in  it 
without  moving  the  jar.     Thus,  if  such  a  jar  were  placed 
over  the  trough,  and  it  were  required  to  raise  the  mercury 
within  an  inch  or  two,  as  in  Lavoisier's  experiment  on  the 
analysis  of  air,  it  is  easily  done  by  passing  one  leg  of  a  glass 
syphon  under  the  mercury  into  the  jar,  applying  the  mouth 
to  the  other  and  ^withdrawing  air  (786).     When  the  mercury 
is  sufficiently  raised,  the  end  of  the  syphon  in  the  mouth  is 
to  be  closed  by  the  tongue,  which  must  not  be  removed  be- 
fore the  other  end  has  been  withdrawn  from  the  jar,  through 
the  mercury,  by  the  same  way  in  which  it  was  introduced. 
Or  if,  during  an  experiment,  the  gas  has  been  absorbed,  and 
the  mercury  stands  very  high  in  a  large  jar,  so  as  to  require 


GASOMETER CONSTRUCTION.  363 

care  in  letting  so  heavy  a  mass  down,  a  syphon  may  be  in- 
troduced as  before,  and  air  allowed  to  pass  into  the  jar 
through  it,  the  mercury  falling  gradually  as  the  air  is  allow- 
ed to  enter.  To  prevent  the  mercury  entering  into  the  sy- 
phon during  the  transit  of  its  extremity  through  the  metal, 
that  end  should  be  closed  by  introducing  a  plug  of  twisted 
paper  into  it,  or  paper  should  be  wrapped  about  it;  either  will 
be  sufficient  to  keep  the  metal  out,  without  stopping  the 
passage  for  the  air. 

§  4.  Of  larger  and  independent  Vessels,  for  the  retaining 
and  storing  of  Gas. 

802.  Numerous  vessels  have  been  contrived  for  the  reten- 
tion of  gas,  independently  of  the  use  of  jars,  or  of  the  water 
or  mercurial  trough,  and  it  is  necessary  that  the  student  be 
acquainted  with  the  principles  and  uses  of  many  of  them. 
All  have  their  respective  conveniences;  some  consisting  in 
great  capacity,  others  in  facility  of  operation,  and  others, 
again,   in  their  security  as  to  the   retention  of  particular 
gaseous  bodies. 

803.  Gasometer.    The  vessel  usually  thus  designated  may 
be  compared  to  a  large  jar  suspended  in  a  trough,  of  size  just 
sufficient  to  allow  its  entire  immersion  in  an  upright  position. 
The  gas-vessel,  or  bell,  instead  of  resting  on  a  fixed  sup- 
port, is  suspended  by  cords  or  chains  passing  over  pullies, 
and  having  weights  at  the  opposite  extremities  to  counter- 
balance the  vessel.     The  trough,  cistern,  or  tank,  as  it  is 
called   in  large  instruments,    is  nearly  filled    with  water, 
which    remains    constant   in    quantity,    the   aerial   capa- 
city within  the  gas-vessel  being  increased  or  diminished  by 
raising  or  lowering  it  in  the  water;  it  is  thus  adapted  to  the 
quantity  of  gas  it  may  contain.     The  passage  of  the  gas  to 
and  from  the  gasometer  is  effected  along  pipes  permanently 
fixed.     A  single  pipe  is  sufficient  in  the  simplest  form  of  in- 
strument, and  this  commencing  at  any  convenient  place  on 
the  exterior  of  the  tank  is  conducted  through  its  bottom, 
and  made  to  rise  so  high  within,  that  its  extremity  shall  be 
above  the  surface  of  the  water.     By  connecting  the  external 


364 


GASOMETER MODE  OF  USING. 


aperture  with  proper  apparatus,  gas  may 
be  made  to  pass  from  it  into  the  gaso- 
meter, or  from  the  gasometer  into  the 
apparatus.  The  accompanying  wood- 
cut, presenting  a  section  of  this  instru- 
ment, will  illustrate  its  principle,  and  as- 
sist the  comprehension  of  the  annexed 
directions  for  its  use.  The  actual  con- 
struction of  the  instrument,  and  its  nu- 
merous variations  inform  and  adjustments, 
make  no  part  of  our  subject.  Gasome- 
ters were  formerly  much  more  used  in  the  laboratory  than 
at  present,  and  great  care  was  paid  to  their  construction,  for 
the  purpose  of  obtaining  an  uniform  pressure.  They  may 
be  made  of  a  great  variety  of  materials.  They  have  of  late 
years  been  constructed  of  enormous  size  in  coal  gas  works, 
and  beautifully  arranged  with  regard  to  their  system  of 
pipes. 

804.  There  is  nothing  difficult  or  particular  in  the  use  of 
a  gasometer.     The  water  in  the  tank  should  never  rise  so 
high  as  to  endanger  its  running  into  the  passage  pipe,  it 
being  necessary  that  this  should  be  preserved  perfectly  free. 
If  water  should,  perchance,  get  into  the  pipe,  it  may  be 
drawn  out  at  the  lower  stop-cock.     The  gas-vessel  should 
be  of  such  depth  as  to  sink  entirely  into  the  water  when 
required,  and  is  advantageously  contracted  above  into   a 
small  chamber,  intended    to  receive  the  end  of  the  pipe, 
and  thus  to  allow  of  the  expulsion  of  nearly  all  the  air  ex- 
cept the  small  portion  the  pipes  may  contain.    When  it  is 
to  be  filled  with  gas,  the  cocks  should  be  opened,  the  bell 
depressed,  until  it  be  as  empty  of  air  as  possible ;  one  of  the 
cocks   is  to  be  shut,  and  the  other  connected  by  a  tight 
joint,  with  the  apparatus  delivering  gas.     This  may  be  a  re- 
tort, or  a  bladder,  or  a  funnel  placed  in  the  water  trough, 
or  in  any  other  vessel.     When  the  operation  is  over,  or  the 
gasometer  sufficiently  full,  the  stop-cock  is  to  be  closed, 
and  the  junction  to  be  disunited. 

805.  When  the  gas  within  the  gasometer  is  required  for 


GASOMETER ADJUSTMENT  OF  PRESSURE,  365 

use,  it  may  be  taken  out  at  that  stop-cock  which  is  most  con- 
venient. If  it  be  desired  to  fill  a  bladder,  it  should  be  at- 
tached to  the  end  of  the  stop-cock;  or  if  a  jar  over  the  pneu- 
matic trough  is  to  be  filled,  a  piece  of  tube  should  replace 
the  bladder,  and  its  open  extremity  pass  into  the  water  of 
the  trough  under  the  jar  (748) ;  or  if  it  be  required  to  pass  a 
stream  of  the  gas  through  a  blow-pipe  (251),  the  blow-pipe 
should  be  attached  to  the  end  of  the  tube  just  mentioned. 

806.  The  entrance  or  exit  of  gas  to  and  from  the  gasome- 
ter is  governed  principally  by  the  pressure  exerted  upon 
the  contents  of  the  vessel ;  this  being  again  dependant,  upon 
the  pressure  exerted  by  or  through  the  bell  itself.     If  the 
hand  press  upon  the  bell  it  presses  also  upon  its  contents; 
in  consequence  of  which  the  water  on  the  outside  rises  to  a 
higher  level  than  that  inside,  and  the  gas  tends  to  issue  by 
any  open  channel,  and  with  a  force  proportionate  to  the 
pressure.     On  the  contrary,  if  the  bell  be  forcibly  raised  by 
the  hand,  the  previous  pressure  is  diminished,  and  to  such 
an  extent  as  to  make  it  less  than  that  of  the  atmosphere  on 
the  exterior;  the  level  of  the  water  without  falls,  and  be- 
comes lower  than  that  within,  and  if  any  passage  be  open, 
the  air  will  enter  into  the  gasometer,  being  forced  inwards 
by  the  superior  external  pressure. 

807.  These  variations  and  arrangements  of  the  pressure 
on  the  contents  of  a  gasometer  are  very  important,  but  in 
practice  they  are  effected  by  the  addition  of  weights  either 
to  the  bell  or  to  its  counterpoise,  or  the  inverse  subtraction 
of  them,  which  has  the  same  effect.     Any  arrangement  of 
weights  which  makes  the  bell  preponderate,  increases  the 
pressure  in  proportion  to  that  preponderance;  the  reverse 
arrangement  diminishes  the  pressure.     Now,  on  receiving 
gas  into  the  instrument,  care  should  be  taken  that  the  pre- 
ponderance of  the  bell  should  be  no  more  than  what  is  easily 
overcome  by  the  effort  of  the  gas  to  pass  in,  and  it  may 
sometimes  be  almost  entirely  removed  with  advantage.     On 
the  contrary,  when  the  gas  in  the  vessel  is  to  be  used,  a 
pressure  outwards  is  required,  more  or  less,  according  to 
the  force  which  opposes  the  transfer;  thus,  but  little  pres- 
sure will  enable  it  to  pass  from  the  gasometer  into  the  air, 
or  into  a  bladder  in  the  air,  though  more  will  be  necessary, 


366 


GASOMETER  EXAMINED PEPYs's. 


when  it  has  to  be  thrown  out  through  an  aperture  at  the 
depth  of  two  or  three  inches  or  a  foot  under  water. 

808.  When  a  gasometer  is  received  from  the  instrument- 
maker,  it  should  in  the  first  place  be  examined  as  to  tight- 
ness.    This  is  done  by  putting  water  into  the  cistern,  then 
half  filling  the  bell  with  air,  closing  the  apertures,  loading 
the  bell  considerably  so  as  to  occasion  much  pressure  out- 
wards, and  leaving  it  so  for  some  hours.     If  at  the  end  of 
that  time  the  bell  has  not  sunk  below  its  first  position,  it 
indicates  the  tightness  of  the  instrument. 

809.  A  mercurial  gasometer  is  the  same  in  principle  as 
those  already  described,  but  in  order  to  avoid  the  weight 
and  expense    which  would  arise  from  filling   the    cistern 
with  mercury,  its  interior  is  principally  occupied  by  a  core, 
allowing  space  enough  between  it  and  the  sides  of  the  cis- 
tern for  the  jar,  and  for  mercury  to  make   it  tight.     The 
first  instrument  of  this  kind  has    been  described  by  Mr 
Clayfield*,  and  was  constructed  of  glass.     To  Mr  Pepysf 
we    are   indebted    for   an    excellent    instrument    of    this 
sort  made  of  iron,  and  having  a  very  convenient  arrange- 
ment  for    the  introduc- 
tion of  gases  from  retorts. 
This  has  been  connected 
by  Mr  Newman  with  his 
large  mercurial  troughf. 
The  accompanying  sec- 
tional diagram  will  illus- 
trate the  arrangement  by 
which  tfye  gasometer  is 
charged :   the  iron  core 
and  the  sides  of  the  cis- 
tern may  be  distinguish- 
ed, and  the  jar  is  seen 
half  full  of  gas,  and  clos- 
ed by  a  stop-cock  above. 
The  core  is  traversed  by 

*  Davy,  Researches,  Chemical  and  Philosophical,  p.  573. 

f  Phil.  Mag,  v.  154. 

|  Quar.  Jour,  of  Science,  i.  185. 


PEPYS'S  MERCURIAL  GAS-HOLDER.  367 

a  perpendicular  passage  consisting  of  a  glass  tube  cemented 
into  its  place,  which  being  open  above  into  the  bell  of  the  gas- 
ometer, terminates  beneath  in  a  stop-cock.  To  this  a  small 
funnel  is  attached  by  a  screw  cap  cemented  upon  it;  and 
beneath  the  funnel  is  placed  a  glass  cup  or  dish  contain- 
ing mercury,  and  raised  so  high  as  to  cover  the  edge  of 
the  funnel,  about  the  third  or  fourth  of  an  inch  in  depth. 
It,  in  fact,  is  a  small  mercurial  trough,  by  means  of  which 
the  gas  from  the  retort  is  made  to  pass  into  the  funnel, 
and  from  thence  through  the  core  into  the  jar  above.  On 
commencing  operations  after  the  gasometer  has  been  filled 
with  mercury,  the  jar  found  to  be  in  order,  the  stop-cocks 
clean  and  moveable,  and  the  trough  beneath  arranged,  the 
first  step  is  to  open  both  stop-cocks,  and  to  depress  the 
jar  in  the  mercury  until  all  the  air  is  excluded,  then  clo- 
sing the  upper  cocks  to  leave  the  jar  to  itself.  The  buoy- 
ancy of  the  glass  in  the  mercury  will  cause  a  tendency 
to  rise,  and  to  cause  also  the  ascent  of  the  mercury  a  little 
way  in  the  funnel  beneath,  above  the  surface  of  that  in  the 
dish.  If,  after  leaving  it  an  hour  or  two  in  this  state,  it  be 
found  that  the  jar  has  not  risen  higher  than  at  first,  the  tight- 
ness of  the  instrument  is  ascertained.  The  beak  of  the  retort, 
or  the  end  of  the  tube  delivering  gas,  is  then  to  be  passed 
beneath  the  edge  of  the  funnel,  the  gas  allowed  to  enter  the 
latter,  and  the  jar  will  be  seen  to  rise  at  every  bubble. 
When  as  much  as  is  equal  to  the  contents  of  the  funnel,  and 
the  tube  of  the  gasometer  has  entered,  the  upper  cock  is  to 
be  opened,  and  the  jar  depressed,  its  contents  thrown  out, 
the  cock  shut,  and  the  gas  collected  as  before.  This  is  to 
be  done  once  or  twice  more,  to  insure  the  rejection  of  all 
common  air,  and  then  the  future  portions  of  gas  are  to  be 
collected  and  preserved  for  use.  When  the  gasometer  is 
full,  the  retort  is  to  be  removed,  the  lower  stop-cock  shut, 
the  temporary  trough  taken  away,  and  the  included  gas  re- 
served until  required.  When  wanted,  it  is  to  be  drawn  off 
from  the  upper  stop-cock,  the  apparatus  being  connected 
with  it  in  the  usual  manner. 

810.  The  gasometer  has  been  to  a  great  extent  super- 
seded  by   another    instrument,  also  the   invention  of   Mr 


368 


PEPYS'S  GAS-HOLDER USES  OF. 


Pepys*,  which  can  hardly  be  dispensed  with  in  the  labora 
toryf .     It  has  been  called  a  gas-holder,  and  is  a  valuable 

vessel  for  the  retention  of  a  stock 
of  oxygen  or  any  other  gas,  which 
is  in  constant  requisition.  It  is 
usually  made  of  japanned  copper, 
and  consists  of  a  close  cylindrical 
vessel,  surmounted  by  a  circular 
trough  of  the  same  diameter,  but 
comparatively  of  small  depth  5  a 
pipe,  a,  proceeds  from  the  bottom 
of  the  trough,  and  passing  through 
the  top  of  the  air-chamber,  de- 
scends until  near  the  bottom,  where 
it  terminates  in  an  open  extremity.  A  second  pipe,  b,  also 
passes  downwards  from  the  trough,  but  merely  enters  into 
the  top  of  the  air-chamber.  Both  these  are  closed  by  stop- 
cocks, /,  h,  placed  between  the  trough  and  chamber.  A 
stop-cock,  g,  is  also  inserted  into  the  top  of  the  air-chamber 
on  one  side,  and  finally  a  short  piece  of  wide  pipe,  c,  enters 
through  the  side  of  the  air-chamber  near  the  bottom,  and 
is  placed  obliquely,  so  that  the  highest  part  of  the  edge 
of  the  inner  aperture  shall  be  lower  than  the  lowest  part 
of  the  edge  of  the  outer  aperture,  by  at  least  half  or  three- 
quarters  of  an  inch.  It  is  closed  and  made  air-tight  occa- 
sionally by  a  plug  which  screws  into  the  aperture.  A  glass 
tube  is  cemented  into  two  sockets  at  d  and  e,  which  opening 
into  the  air-chamber,  render  the  tube  in  fact  a  part  of  that 
cavity ;  its  use  is  to  indicate  the  quantity  of  water,  and  con- 
sequently the  quantity  of  gas,  within.  All  the  joints  and 
seams  should  be  perfectly  air-tight;  this  point  may  be  ascer- 
tained in  the  following  manner.  The  aperture  c  being  closed 
by  its  proper  plug,  the  three  cocks  above  are  to  be  opened, 
and  water  poured  into  the  trough  and  allowed  to  descend 
into  the  air-chamber  until  it  is  full;  the  vessel  is  then  to  be 
inclined  a  little,  the  lateral  stop-cock  being  raised  upwards 

*  Phil.  Mag.  xiii.  153. 

t  A  copper  gas-holder,  placed  beneath  the  shelf  of  the  pneumatic  trough,  will 
be  found  more  convenient  than  any  other  instrument  of  the  kind,  both  for  collec- 
tion and  transfer.— ED. 


PEPYS'S  GAS-HOLDER — HOW  FILLED.  369 

so  that  the  air  may  escape  by  it  until  water  only  issue.  This 
and  the  other  stop-cocks  are  then  to  be  closed,  and  the  guage 
observed  to  ascertain  whether  the  vessel  be  full  of  water, 
or  if  a  bubble  of  air  be  at  the  top,  to  mark  the  place  where 
it  stands.  The  plug  at  c  is  then  to  be  unscrewed  and  re- 
moved. The  water  cannot  escape  there  in  consequence  of 
the  manner  in  which  the  pipe  c  is  inserted,  unless  the  air 
finds  access  inwards  above  at  the  same  time ;  and  if  there 
should  be  any  leak,  the  weight  and  tendency  of  the  water 
to  descend  will  draw  the  air  through  it.  Upon  standing 
therefore  a  few  hours,  it  will  be  easy  to  ascertain  by  the 
guage  whether  the  vessel  be  tight :  i.  e.  whether  any  air  has 
gained  access,  or  any  water  has  run  out  excepting  the  first 
small  portion. 

811.  The  process  of  filling  this  vessel  with  gas  is  exactly 
the  same  in  principle  as  filling  o  jar  over  the  pneumatic 
trough.     The  stop-cocks  are  to  be  closed,  the  aperture  c 
opened,  and  the  beak  of  the  retort  or  the  tube  delivering  gas 
is  to  be  introduced  at  c ;  the  gas  will  bubble  up  through  the 
water  and  displace  the  fluid.     Provision,  however,  is  to  be 
made  to  convey  away  the  water.     For  this  purpose  the  gas- 
holder may  be  filled  near  the  sink,  and  the  water  allowed  to 
run  out ;  or  if  it  has  to  be  brought  towards  the  furnace,  as 
in  the  making  of  oxygen  gas,  it  may  be  mounted  on  a  stool, 
and  the  water  received  into  a  pail  placed  beneath  the  open- 
ing.    In  such  cases  it  will  be  found  useful  to  hang  a  piece 
of  wet  tow  about  the  tube  conducting   the  gas,  so  as  to  be 
in  contact  with  the  edge  c ;  this  will  lead  the  water  into  the 
pail  (468). 

812.  The  descent  of  the  water,  and  therefore  the  quantity 
of  gas  introduced,  is  indicated  by  the  guage.     When  the  gas 
bubbles  out  at  c,  the  vessel  can  retain  no  more  :  the  tube  or 
retort  is  to  be  withdrawn,  the  plug  screwed  up  tight,  and  in 
that  state  the  gas  is  securely  confined,  and  may  be  preserved 
for  many  months  provided  water  is  retained  in  the  trough 
above. 

813.  No  difficulty  occurs  in  transferring  the  gas  from  this 
vessel  into  any  other  that  may  be  required.   The  lower  aper- 
ture is,  in  these  cases,  of  no  use,  and  is  to  be  kept  closely 

2  W 


370  PEPYS'S  GAS-HOLDER TRANSFERENCE. 

shut.  Upon  opening  the  stop-cock  of  the  pipe  a,  the  water 
will  flow  down  it  to  the  bottom  of  the  air-chamber  until  such 
time  as,  having  accumulated  there,  the  gas  above  is  com- 
pressed by  a  force  equal  to  the  weight  of  the  column  of  wa- 
ter in  the  tube  and  trough.  No  more  water  will  then 
descend  unless  the  stop-cock  /  or  g  be  opened,  when  the 
gas  will  immediately  rush  out,  urged  on  by  the  column  of 
water  in  the  tube,  and  the  water  above  will  supply  its  place. 
The  process,  therefore,  of  filling  a  jar  or  a  bladder,  or  pass- 
ing the  gas  through  a  tube,  is  very  simple.  In  transferring 
it  to  a  jar,  for  instance,  the  latter  must  be  first  filled  with 
water,  inverted  (753)  in  the  water  of  the  trough,  and  placed 
over  the  aperture  of  the  pipe  b ;  then  having  opened  h  as 
before  described  for  the  purpose  of  causing  pressure  on  the 
gas  within,  the  stop-cock  f  is  to  be  carefully  opened,  when 
the  gas  will  rush  up  and  quickly  fill  the  jar.  The  water 
from  the  jar  descends  into  the  trough  to  supply  the  place  of 
that  which  passes  into  the  air-chamber.  The  cock  /  is  to 
be  closed  as  soon  as  enough  gas  has  passed  out,  when  h  is 
to  be  shut,  the  jar  of  gas  transferred  and  used  as  may  be  re- 
quired. Or  suppose  that  a  bladder  is  to  be  filled  with  gas : 
the  common  air  is  first  to  be  thrown  out-,  the  bladder  attached 
to  the  cock  g,  pressure  is  to  be  given  by  opening  h,  then  g  is 
to  be  cautiously  opened,  and  the  bladder  to  be  filled  ;  the 
water  which  is  necessary  being  supplied  to  the  trough  above 
from  a  jug  or  pail ;  finally,  the  cocks  g  and  h  are  to  be  shut, 
and  the  bladder  removed. 

814.  It  is  sometimes  necessary  to  introduce  gas  from  a 
bladder  into  the  gas-holder.     In  that  case  the  full  bladder  is 
to  be  attached  to  the  cock  g,  all  the  cocks  being  closed;  the 
plug  at  c  is  to  be  opened,  and  then  the  cock  at  g  cautiously 
turned  to  allow  the  gas  to  pass  in,  the  water  at  the  same  time 
passing  out;  the  cock  is  then  to  be  closed  and  finally  the 
plug  c. 

815.  If  the  transfer  of  gas  is  to  be  effected  through  a  tube, 
as  for  instance,  in  arranging  the  oxygen  blow-pipe  (251),  or 
supplying  inflammable  air  to  a  jet,  the  pipe  must  be  attached 
to  the  cock  g;  the  pressure  of  water  given  as  before,  and  the 
emission  of  gas  regulated  by  the  extent  to  which  the  stop- 
cock g  is  opened. 


GAS-HOLDER — TRANSFER PRECAUTIONS.  37 1 

816.  The  inventor  has  provided,  even  for  occasions  on 
which  a  greater  pressuce  than  that  of  two  feet  of  water  may 
be  required,  by  associating  a  long  tube  and  funnel  with  the 
instrument.     This  being  screwed  into  the  mouth  of  the  pipe 
a,  where  it  enters  the  trough  above,  and  retained  full  of  water, 
subjects  the  gas  in  the  instrument  to  the  pressure  of  a  co- 
lumn four  feet  in  height,  and  is  occasionally  very  useful. 

817.  It  requires  no  particular  skill  to  make  one  of  these 
air  holders  out  of  a  good  cask  by  the  addition  of  a  few  tubes, 
cocks,  and  a  funnel:  but  it  must  always  be  retained  moist. 

818.  It  is  essentially  necessary  that  in  all  the  transfers  of 
gas/rom  the  instrument,  an  abundance  of  water  be  retained 
in  the  trough  above,  to  supply  the  place  of  that  which  passes 
into  the  air-chamber.     It  is  also  necessary  to  be  aware  of 
the  possible  introduction  of  common  air  with  the  water,  even 
when  there  is  considerable  depth  in  the  trough.     When  the 
gas  is  passing  rapidly  out  at  the  lateral  stop-cock,  and  conse- 
quently the  water  rapidly  descending  through  the  tube,  it 
will,  if  unattended  to,  frequently  acquire  a  rotary  motion, 
which,  from  mechanical  causes  easily  explained,  will  at  last 
produce  an  aperture  commencing  at  the  surface  of  the  water 
and  descending  to  the  very  bottom  of  the  tube.     Down  this, 
air  is  rapidly  carried  by  the  descending  water,  which,  mixing 
with  the  gas  in  the  instrument,  deteriorates  it,  and  with  in- 
flammable gases  may  lead  to  dangerous  results.     Hence  this 
rotary  motion,  when  observed,  should  be  disturbed.     The 
formation  of  the  central  channel  for  air  may  easily  be  pre- 
vented by  allowing  a  large  bung  or  a  piece  of  light  wood  to 
swim  on  the  surface  of  the  water.  If  rotation  does  take  place, 
it  will  draw  the  floating  mass  to  the  centre,  and  prevent  the 
air  from  passing  down  by  hindering  the  formation  of  a  chan- 
nel, if  water  be  plentifully  supplied. 

819.  When  gas-holders  are  to  be  left  for  several  weeks 
or  longer  with  gas  in  them,  it  is  advantageous  to  put  a  board 
over  the  water  in  the*cistern  or  upper  part.     It  prevents  the 
evaporation  of  the  flutd  too  rapidly,  and  retains  all  in  order. 

820.  Amongst  vessels  for  the  retention  of  gas  may  be 
classed  bladders  and  bags;  they  are  very  useful  in  many  re- 
ceiving or  transferring  operations,  or  when  subjected   to 


372  GAS-VESSELS BAGS —  PERMEABILITY. 

pressure,  in  supplying  a  constant  stream  of  gas  for  a  length  of 
time.  Bladders  of  different  sizes  are  required.  The  necks 
should  be  softened  by  water,  opened,  drawn  over  the  lower 
part  of  a  cap  similar  to  a  retort  cap  (833),  and  tightly  tied 
with  twine.  A  stop-cock  screwed  into  the  cap  renders  the 
vessel  complete.  If  the  bladders  are  used  in  a  dry  state,  the 
mechanical  action  to  which  the  membrane  is  subjected  during 
expansion  and  contraction,  and  otherwise,  soon  breaks  the 
substance,  and  they  become  useless.  To  prevent  this,  and 
also  to  remove  their  rigidity,  which  is  inconvenient,  bladders 
are  commonly  moistened  before  being  used.  This  renders 
them  very  conveniently  flexible  for  present  purposes,  but  they 
become  more  and  more  rigid  each  time  they  are  wetted  and 
dried,  and  soon  break  into  holes.  A  bladder  may  be  made 
to  continue  tight  for  a  considerable  period  by  pouring  a 
little  oil  into  it  at  first,  and  allowing  it  to  become  saturated. 
It  is  not,  then,  to  be  wetted  for  use,  but  is  at  no  time  so  plea- 
sant to  work  with  as  a  wet  bladder.  Bladders  should  be 
kept  in  a  moderately  expanded  state,  not  tightly  blown,  nor 
on  the  contrary  compressed  together;  and  this  is  more  par- 
ticularly necessary  with  those  bladders  which  are  wetted  each 
time  they  are  used,  and  are  laid  aside  in  a  moistened  state. 
Bladders  are  not  perfectly  tight  to  gases,  and  are  less  so 
when  dry  than  when  moist;  consequently  gases  should  not 
be  retained  long  in  them,  and  never  longer  than  is  absolutely 
necessary.  Hydrogen  passes  through  them  more  rapidly 
than  any  other  gas.* 

821.  Gas-bags  are  made  of  oiled  silk,  or  of  two  layers  of 
woven  material,  having  between  them  a  layer  of  caoutchouc 
orJndian  rubber,  which  serves  to  bind  the  whole  into  one 
impervious  substance  ;  they  are  furnished  with  a  cap  and 
stop-cock,  like  the  bladders  just  described.  Those  made  of 
oiled  silk  are  seldom  tight,  and  rapidly  increase  in  porosity. 
Those  manufactured  with  caoutchouc  are  superior,  and  when 
the  substance  has  been  prepared  for*this  purpose  with  a 
thick  coat  of  that  peculiar  body,  may%e  made  permanently 

*  Ammonia,  cyanogen,  carbonic  acid  gas,  nitrous  oxide  and  sulphuretted  hy- 
drogen pass  through  all  membranes  much  more  rapidly  than  hydrogen.  Vide 
Amer.  Journ.  of  the  Med.  Sci.  for  November  1830. — ED. 


GAS-BAGS CAOUTCHOUC OILED  LEATHER.  373 

air-tight*  It  is,  however,  to  be  understood,  that  the  fabrics 
sold  as  water-proof,  and  stated  to  be  made  so  by  caoutchouc, 
are  no*t  sjlficiently  air-tight  for  these  applications.  These 
bladders  and  bags  are  useful  in  transferring  gases  from  vessel 
to  vessel,  as  between  jars  and  air-holders;  and  when  filled 
and  covered  with  a  weighted  board,  they  will  supply  a  con- 
stant stream  of  gas  for  a  length  of  time.f 

822.  Caoutchouc  or  Indian  rubber  bottles  are  useful  ves- 
sels in  particular  circumstances,  and  may  be  had  at  the  in- 
strument-makers;  their  uniform  expansion  in  all  directions 
having  been  previously  ascertained.      It  is  necessary  to  in- 
troduce the  gas  by  a  condensing  syringe,  in  consequence  of 
the  force  required  to  dilate  the  bottle  ;  but  being  introduced, 
the  spontaneous  contraction  of  the  caoutchouc  upon  it  is  very 
useful  in  forcing  it  out  through  the  stop-cock,  and  hence  the 
particular  uses  of  these  bottles  (252).     A  bottle,  at  first  not 
more  than  three  inches  in  diameter,  may  be  extended  till  it 
contains  half  a  cubic  foot  of  gas  or  more,  and  upon  allow- 
ing its  contents  to  escape,  will  contract  to  nearly  its  original 
size. 

823.  Those  who  endeavour  to  prepare  these  bottles  for 
themselves,  will  not  succeed  with  more  than  one  in  four  or 
five.     They  should  be  selected  of  uniform  thickness,  and 
without   external  marks  or  depressions ;  those   which  are 
lightest  in  colour  are  generally  best.   They  should  be  heated 
in  hot  water,  or  hi  steam,  for  an  hour  or  two,  and  then  rolled 
between  the  hands  until  they  become  perfectly  flexible  ; 
when  cold  they  should  be  tied  upon  caps,  having  a  stop-cock 
and  a  syringe  attached ;  the  air  is  then  to  be  gradually 
thrown  in.     The  bottle,  when  fully  distended,  generally  be- 
comes thin  at  one  place  first;  if  upon   expansion  by  air  this 
thinness  extend  to  the  neighbouring  parts,  all  is  well ;  but 
if  it  increase  rapidly  and  partially,  there  is  little  chance  of 
the  bottle  being  made  useful.     The  air  should  be  introduced 
in  successive  portions,  a  lapse  of  time  being  allowed  after 
every  few  strokes  of  the  piston,  especially  during  the  first 

*  Air-tight  only  when  filled  with  common  air.— ED. 

f  Dr  Hare  employs  bags  formed  of  oiled  leather,  the  seams  of  which  are  closed 
by  metallic  rivets,  such  as  are  used  in  forming  leathern  water  pipes,  hose,  &c. 
—ED. 


374        CAOUTCHOUC  BAGS — PREPARATION  OF. 

expansion.  Caoutchouc  bottles,  thus  fully  expanded  and 
rendered  thin,  should  not  be  exposed  to  heat  on  one  side 
only  or  partially;  for  the  heat,  diminishing  the  cohesfre  at- 
traction, allows  the  neighbouring  parts  to  contract  by  dis- 
tending the  heated  part,  which,  becoming  gradually  thinner, 
at  last  bursts  into  a  hole.^ 

824.  Finally,  glass  bottles  are  frequently  of  great  service 
in  the  retention  and  preservation  of  gases,  and  more  espe- 
cially of  chlorine  gas,  which  cannot  be  retained  for  any 
length  of  time  over  water,  in  which  it  dissolves,  or  over  mer- 
cury, on  which  it  acts.  The  bottles  should  be  wide-mouthed 
and  accurately  stoppered  (433),  their  capacities  being  from 
four  or  six  ounces  to  a  quart.  The  necks  and  the  stoppers 
should  in  the  first  place  be  wiped  dry,  a  little  tallow  or  lard 
applied  to  the  stopper,  and  the  latter  moved  round  in  its 
situation,  so  as  to  disperse  the  tallow  over  the  ground  sur- 
faces, and  render  the  stopper  easy  in  its  motion  and  at  the 
same  time  air-tight.  The  bottles  should  then  be  filled  with 
gas  as  if  they  were  jars  (751),  the  stoppers  put  in  under 
water,  and  pressed  into  their  places,  and  then  the  bottles  be 
stored  away  in  a  dark  place  of  nearly  uniform  temperature, 
in  an  inverted  position,  and  with  the  stopper  and  neck  im- 
mersed in  water.  This  may  be  done  by  providing  earthen- 
ware jellypots,  or  similar  vessels,  one  for  each  bottle.  When 
water  is  put  into  these,  and  the  bottles  inverted  in  them,  the 
gas  is  rendered  perfectly  secure,  and  may  be  preserved  for 
months,  and  even  years.  These  receiving  vessels  may  be 

*  The  following  is  an  easy  mode  of  making  caoutchouc  bags. — Soak  the  com- 
mon bags  in  sulphuric  ether — sp.  grav.  753,  at  a  temperature  not  less  than  50* 
Fahr.  for  a  period  of  time  not  less  than  one  week  (the  longer  the  better). 
Empty  the  bag,  wipe  it  dry,  put  into  it  some  dry  powder,  such  as  starch,  insert 
a  tube  into  the  neck,  and  fasten  it  by  a  broad  soft  band  slightly  applied,  and  then 
commence  by  mouth  or  bellows  the  inflation.  If  the  bag  be  unequal  in  thick- 
ness, restrain  by  the  hand  the  bulging  of  the  thinner  parts,  until  the  thicker  have 
been  made  to  give  way  a  little. — When  the  bag  has  become  by  such  means 
nearly  uniform,  inflate  a  little  more,  shake  up  the  included  starch,  and  let  the  bag 
collapse.  Repeat  the  inflation,  and  carry  it  to  a  greater  extent,  again  permit  the 
collapse,  again  inflate  still  more  extensively,  and  so  on,  until  the  bag  is  suffi- 
ciently distended.  Mere  gas  holders  are  thus  easily  made,  but  it  requires  some 
dexterity  and  experience  to  make  them  thin  enough  for  balloons.  The  whole  ex- 
periment should  not  occupy  more  than  from  five  to  twenty  minutes  of  time.  And 
the  prepared  bag  should  be  closed  and  hung  up  to  dry  for  a  day  or  two. — Vide 
Silliman's  Chemistry. — ED. 


GLASS  GAS-BOTTLES MODE  OF  USING.  375 

conveniently  made  out  of  fractured  wine  bottles,  when  they 
remain  sound  towards  the  bottom,  the  upper  part  being  cut 
off  by  a  hot  iron  or  otherwise  (1214). 

825.  Dry  bottles  may  be  filled  with  such  gases  as,  being 
either  much  heavier  or  lighter  than  atmospheric  air,  are  at 
the  same  time  soluble  in   water,  and  cannot  be  collected 
over  that  fluid.  For  light  gases,  such  as  ammonia,  the  bottle 
to  be  filled  is  to  have  its  stopper  greased,  and  is  then  to  be 
placed  in  a  vertical  position,  with  the  mouth  downwards 
over  the  end  of  the  tube  or  retort  neck  delivering  the  gas, 
which  at  the  same  time  is  to  be  directed  upwards,  until  it 
touches  the  bottom  of  the  bottle ;  the  light  gas  occupies  the 
upper  part  of  the  vessel  at  first,  and  gradually  displaces  the 
air :  ultimately,  from  the  addition  of  fresh  portions  above,  it 
flows  out  at  the  mouth  of  the  bottle,  and  when  by  applying 
a  slip  of  moistened  turmeric  paper  to  the  aperture,  it  is  judged 
from  the  change  produced  that  the  gas  in  the  bottle  is  nearly 
or  quite  pure,  the  tube   or  retort  is  to  be  gradually  with- 
drawn, with  as  little  disturbance  of  the  gas  within  as  possible, 
and  the  stopper  instantly  put  into  its  place. 

826.  Many  gases,  such  as  muriatic,  sulphuric,  or  carbonic 
acid  gas,  are  on  the  contrary  conducted  downwards  to  the 
bottoms  of  bottles  placed  with  their  mouths  upwards,  which 
when  they  freely  overflow  with  gas  at  their  mouths,  are  to 
be  withdrawn  and  quickly  stopped.    The  overflowing  of  the 
muriatic  acid  gas  is  known  by  the  fumes  which  seem  to  issue 
from  the  mouth  of  the  bottle.     The  fulness  of  vessels  receiv- 
ing sulphurous  or  carbonic  acid  gases  may  be  ascertained 
by  bringing  a  lighted  taper  carefully  near  the  mouth,  the  ra- 
pidity and  appearance  of  its  extinction  being  a  sufficient  in- 
dication.    In  all  these  cases  it  is  necessary  to  allow  an  ex- 
cess of  gas  to  pass  through  the  bottles,  and  to  continue  the 
introduction  of  fresh  gas  even  after  the  bottle  is  supposed 
to  be  full,  a  portion  being  willingly  thrown  away  to  insure 
the  greater  purity  of  that  which  is  retained.     The  gases 
above  mentioned   may  readily  be  collected,   especially  in 
small  bottles,  intermixed  with  not  more  than  between  a  fif- 
tieth and  a  hundredth  part  of  common  air.* 

*  It  is   somewhat  singular,  that  our  judicious   author  should   have  omit- 


376 


HARE'S  SELF-REGULATING  GAS-HOLDER. 


§  5.  Connexion  and  Communication* 

827.  Having  already  had  occasion  to  mention  caps  and 
stop-cocks,  it  will  be  necessary  more  particularly  to  consid- 
er the  general  uses  and  arrangement  of  these  and  other 
pieces  of  apparatus,  intended  to  facilitate  the  connexion  or 
disjunction  of  different  instruments,  or  the  different  parts  of 
a  complicated  arrangement.  Laboratory  stop-cocks  are 
usually  made  of  brass,  and  are  terminated  by  a  male  screw 
at  each  end  rising  from  a  flat  shoulder,  so  that  the  interven- 
tion of  a  washer,  or  collar  of  leather  (830)  renders  them, 
when  screwed  up  into  their  proper  apertures,  perfectly  air- 
tight. The  plug  of  the  cock  should  be  very  accurately 
ground  into  its  socket,  that  no  air  may  pass  it.  It  is  usually 
held  in  its  place  by  a  collar  and  screw,  so  that  the  experi- 
menter can  take  it  out,  examine  it,  and  apply  a  little  wax  or 
fat,  whenever  there  may  be  occasion.  The  passage  through 
the  cock  should  not  be  more  than  one-eighth  of  an  inch  in 


ted  to  mention  the  self-regulat- 
ing reservoir  of  Gay  Lussac,  and 
the  still  more  convenient  one  of  Dr 
Hare.  The  cut  represents  Hare's 
instrument,  in  the  interior  and  in- 
verted vessel  of  which,  is  placed 
the  substance  to  be  acted  on  by 
the  liquid  contained  in  the  outer 
and  erect  cistern.  When  the  in- 
verted vessel  is  filled  with  gas  or 
air,  the  liquid  has  not  access  to  the 
solid;  but  as  the  gas  is  made  to  es- 
cape through  the  pipe  placed  at  the 
apex,  the  liquid  rises  into  it,  and 
new  portions  of  gas  are  generated, 
and  in  their  turn  expel  the  liquid. 
This  ingeniously  contrived  appara- 
tus is  both  retort  and  gas-holder, 
always  ready  for  service,  and  con- 
stantly reproductive  of  its  con- 
tents.— ED. 


STOP-COCKS EXAMINED TIGHTNESS.  377 

diameter,  and  is  even  advantageously  smaller  where  it  pas- 
ses through  the  plug,  for  then  its  section  upon  the  plug  and 
socket  is  diminished,  and  the  tightness  and  security  of  the 
cock  increased. 

828.  These  stop-cocks  are  necessarily  subject  to  injury 
during  use,  many  gases,  as  chlorine,  ammonia,  &c.  having 
powerful  action  upon  the  metal:  they  should  be  frequently 
looked  at,  examined,  and  the  plug  lubricated  (827,  433). 
It  is  often  necessary  to  cleanse  the  air-way,  and  remove  such 
obstructing  matter  as  has  either  collected  or  been  formed 
there.     This  may  be  done  with  a  stiff  wire  ;   but  particular 
care  should  be  taken,  in  such  operations,  that  the  plug  itself, 
or  its  socket,   be  not  scratched,  or  the  apertures  formed  by 
the  air-way  upon  their  surfaces  injured,  which  would  soon 
destroy  the  tightness  of  the  instrument,  and  render  it  useless. 
The  plug  when    turned  round    in  its  socket  should  move 
easily  and  steadily,  allow  of  no  shake  in  any  direction,  and 
not  permit  air  to  pass.     For  this  purpose,  even  when  new,  a 
little  wax  or  grease  should  be  applied.     Tallow  is  the  sub- 
stance usually  resorted  to,  but  a  mixture  of  two  parts  yellow 
wax  and  one  part  sweet  oil  is  much  better,  since  it  preserves 
the  tightness  of  a  stop-cock  that  is  slightly  injured,  longer 
than  tallow  or  pomatum.     The  plug  and  socket  of  a  foul 
stop-cock  should  be  cleaned  with  a  cloth,  and  not  with  a 
hard  instrument. 

829.  If  the  plug  adhere,  as  though,  from  chemical  action 
or.  otherwise,  it  had  become  so  fixed  as  to  be  almost  immov- 
able, its  screw  and  collar  are  to  be  removed,  and  by  tapping 
the  end  with  wood  (not  with  metal)  attempts  are  to  be  made 
to  drive  it  out  of  its  place.     If  it  resist  this,  and  also  some 
degree  of  force  applied  to  turn  it,  a  little  oil  is  to  be  drop- 
ped in  at  each  end  of  the  stop-cock,  and  also  applied  to  the 
end  of  the  plug,  and  then  the  whole  should  be  warmed  and 
left  for  an  hour  or  two,  when  it  may  generally  be  moved. 
The  plug  of  an  old  stop-cock  commonly  requires  more  wax 
or  tallow  than  a  new  one ;  this  should  not  be  allowed  to  ac- 
cumulate in  the  air-way,  where  it  is  of  no  use,  but  a  little 
piece   being  put  upon  each  side  of  the  clean  dry  plug,  the 
latter  is  to  be  introduced  into  the  socket,  equally  clean  and 

2  X 


378  STOP-COCK WASHERS. 

dry,  and  then  turned  round  a  few  times  to  effect  its  equal 
and  proper  distribution.  When  chlorine  or  ammonia  has 
passed  through  the  stop-cocks,  the  sooner  they  are  looked 
at  and  aired  or  washed  as  occasion  may  require,  the  better. 

830.  Washers  or  collars  are  round  pieces  of  soft  substan- 
ces, as  leather  or  paper,  which,  having  holes  in  the  middle, 
are  passed  over  the  male  screws  of  the  stop-cocks,  so  that 
when  the  latter  are  connected  with  other  apparatus,  the 
washers  are  between  their  shoulders  and  the  sides  of  the 
aperture  into  which  the  cocks  are  screwed,  and  make  the 
joints  impervious.     They  are  usually  punched  out  of  thin 
boot  or  shoe  leather,  and  the  pieces  being  soaked  in  oil  for 
a  day  or  two  and  then  cleaned,  are  ready  for  use.     It  is  bet- 
ter for  many  purposes  to  use  wax  instead  of  oil  on  these  oc- 
casions.    Yellow  wax  should  be  melted  and  the  washers 
put  into  it  for  five  minutes  ;  when  taken  out,  they  are  to  be 
allowed  to  drain  a  moment  or  two,  and  suffered  to  cool. 
When  required  for  use,  they  should  be  rendered  flexible  by 
the  warmth  of  the  hand,  before  they  are  put  into  their  places. 
Such  collars  will  occasionally  remain  tight  for  hours  together 
at  a  pressure  of  from  ten  to  thirty  atmospheres,  when  an 
oiled  washer  would  inevitably  have  leaked ;  and  they  are 
more  secure  and  constant  even  at  common  pressures. 

831.  When  the  joint  has  to  bear  a  temperature  near  to  or 
above  2 12°,  one  or  more  thicknesses  of  card  answer  the  pur- 
pose of  a  collar  better  than  leather.  Sheet  caoutchouc  (449), 
similar  to  that  prepared  by  Mr  Hancock,  may  be  formed 
into    excellent  collars  for    particular  occasions,  but  it  is 
necessary  to  be  cautious  in  screwing  up  the  joint.     Caout- 
chouc, from  its  elasticity,  becomes  readily  adapted  to  the 
surfaces  immediately  upon  contact,  so  that  but  little  press- 
ure renders  the  joint   perfectly  tight.      On  the  contrary, 
were  the  cock  tightly  screwed  up,  the  force  would  be  suffi- 
cient to  press  out  nearly  all  the  caoutchouc  at  the  edges  of 
the  joint;  this,  although  it  would  not  destroy  the  tightness  of 
the  arrangement,  would  be  of  no  use,  and  would  injure  the 
collar  and  spoil  it  for  future  service.*  All  dirt  should  be  re- 

*  The  adhesive  character  of  caoutchouc  makes  grease  indispensable  to  the  use- 
fulness of  such  washers.  Without  it,  they  are  thrown  into  folds  by  the  rotating 
shoulder. — ED. 


STOP-COCK OF  GRIFFITHS— CRIVELLI HARE.  379 

moved  from  the  surface  of  the  shoulders  before  the  collars 
are  put  on,  or  otherwise  it  will  occasion  irregular  pressure, 
and  interfere  with  the  tightness  of  the  joint. 

832.  Some  variations  in  the  ordinary  chemical  stop-cock 
have  been  recommended,  but  have  not  been  received  into 
common  use.  Mr  Griffiths  advises  thatthe  air-way  be  lined 
by  a  tube  of  platinum,  so  as  to  prevent,  to  a  considerable  de- 
gree, the  action  of  gases  and  other  substances  passing  through 
or  retained  in  it*.  Signer  Crivelli  has  combined  a  conical 
metallic  valve  with  the  stop-cock,  for  the  purpose  of  render- 
ing it  more  tight  and  manageable  when  employed  to  retain 
gases  under  great  pressuref. 

[At  the  request  of  the  Editor,  Dr  Hare  has  furnished  the 
two  following  paragraphs. 

"  This  figure  is  intended  to  illustrate  the  construction  of  a 
substitute  for  a  common  cock  which  I  have  been  accustomed 
tocallavalve  cock.  It  was  devised  by  me  about  twenty  years 
ago,  among  a  number  of  other  analogous  contrivances,  and 
seems  upon  the  whole  less  liable  to  fail  than  any  other  which 
I  have  tried.  The  engraving  represents  a  longitudinal  sec- 
tion of  the  valve-cock.  At  a,  is  a  piston  with  a  collar  en- 
closed in  the  stuffing-box  6,  so  as  to  be  rendered  air-tight 
by  means  of  oiled  leather.  Hence  this  piston  may  be  turned 
or  made  to  revolve  on  its  axis,  while  incapable  of  other  mo- 
tion. Upon  the  end  of  the  piston  a  thread  for  a  screw  is  cut 
which  fits  into  a  female  screw  in  the  brass  prism  c,  so  as  to 
cause  this  prism  to  approach  to  or  retreat  from  a  bearing  cov- 
ered by  leather,  in  the  centre  of  which  there  is  a  perforation 
o  o,  communicating  with  one  of  the  orifices  of  the  instrument. 
This  orifice  is  surrounded  by  the  male  screw  d,  so  that  by 
means  of  this  screw,  the  valve  cock  may  be  fastened  into  an 
appropriate  aperture,  properly  fitted  to  receive  it,  subjecting 
an  interposed  leather  to  such  a  pressure,  as  to  create  with  it 
an  air-tight  juncture.  The  prism  c,  has  two  of  its  four  edges 
cut  off  (see  fig.  2.)  so  as  to  allow  a  free  passage  by  it,  reach- 
ing to  the  lateral  perforation  terminating  in  another  orifice, 
over  which  there  is  agallows  screw  g.  Bymeansofthisgallows 
screw,  when  requisite,  a  brass  knob,  such  as  that  represented 

*  Transactions  of  the  Society  of  Arts,  xlii.  p.  29. 
t  Quarterly  Journal  of  Science,  viii.  p.  346. 


380 


HARE'S  VALVE-COCK — RETORT-CAPS. 


by  fig.  3,  soldered  to  a  leaden  pipe,  may  be  fastened  to  the 
valve  cock.  This  juncture  is  rendered  air-tight  by  the  press- 
ure of  the  screw  in  the  gallows  upon  a  leather,  which  is  kept 
in  its  place  by  means  of  the  nipple  n. 

"  The  method  last  mentioned,  of  producing  an  air-tight 
juncture,  was  contrived  by  me  about  seven  years  ago,  and 
proves  to  be  of  very  great  utility.  There  is  no  other  mode 
with  which  I  am  acquainted,  of  making  a  perfectly  air-tight 
communication  between  cavities  previously  separate,  at  all 
comparable  to  this,  in  facility."] 

833.  Retort  caps  are  cylinders  of  thin  brass  plate,  con- 
tracted at  one  extremity  by  the  insertion  of  a  thick  ring,  in 
which  a  female  screw  is  cut,  and  turned  flat  at  the  end  so 


RETORT-CAPS EXAMINED ATTACHED.  381 

as  to  screw  up  tightly  against  the  shoulder  of  the  stop-cock. 
These  caps  are  of  various  diameters  to  fit  tubes  and  necks 
of  retorts  of  different  sizes.  The  flat  extremity  at  the  head 
of  the  cap,  which  screws  up  against  the  shoulder  of  the  stop- 
cock, should  have  two  or  three  concentric  grooves  (merely 
deep  lines)  turned  in  it,  which  will  render  its  bearing  against 
the  collar  more  air-tight  and  secure.  These  lines  or  grooves 
should  be  kept  free  from  dirt  by  having  a  point  run  along 
them  occasionally,  and  the  worm  of  the  screw  should  also 
be  preserved  clean  and  free  from  obstructing  matter. 

834.  Caps  are  fastened  upon  the  ends  of  tubes  or  retorts 
with  a  particular  cement  (1123),  in  the  following  manner. 
One  is  to  be  selected  of  such  size  as  to  admit  the  tube  and 
allow  a  space  for  cement  about  the  thickness  of  a  card,  or  a 
little  more,  but  the  cap  should  never  be  so  small  as  itself  to 
gripe  the  glass,  or  any  larger  than  is  necessary  to  allow  room 
for  cement  to  surround  the  glass.  The  cement  should  be 
heated  to  fluidity  on  the  sand-bath,  but  not  to  a  greater  de- 
gree; the  cap  should  be  warmed  over  a  candle  or  lamp  until 
it  is  hot  enough  to  melt  cement,  and  then  that  part  of  its  in- 
terior which  is  intended  to  come  against  the  glass,  namely, 
the  sides  of  the  cylinder,  should  be  covered  with  the  hot 
cement,  applied  by  a  piece  of  stick.  The  cap  being  then 
laid  on  its  side  by  the  sand-bath  to  keep  it  from  cooling,  the 
end  of  the  tube  or  retort  is  next  to  be  warmed,  and  a  coat  of 
cement  applied  on  the  exterior,  over  every  part  which  is  to 
come  into  juxtaposition  with  the  cap,  but  the  other  parts  are 
not  to  be  unnecessarily  soiled  ;  so  much  cement  is  to  be 
left  adhering  to  the  glass,  that  with  what  there  is  in  the  cap, 
there  may  be  an  excess  above  the  quantity  that  can  be  re- 
tained between  the  glass  and  metal  when  the  two  are  fitted 
together.  When  the  cap,  glass,  and  cement,  are  all  so 
warm  that  the  latter  is  fluid,  or  very  soft,  the  cap  is  to  be 
placed  upon  the  tube,  thrust  into  its  right  position,  receiving 
a  little  rotary  motion  at  the  same  time,  to  distribute  the 
cement  equally  over  all  parts,  and  is  afterwards  to  be  set 
aside  to  cool.  When  this  is  well  performed,  the  retort  neck, 
or  tube,  should  pass  along  until  it  be  stopped  by  the  inside 
of  the  shoulder ;  no  cement  should  soil  its  interior,  or  project 
within  the  cap,  but  it  should  fill  every  part  between  the  glass 


382  CONNECTERS — SCREWS. 

and  cap,  to  make  a  firm,  tight  junction,  and  project  in  a  ring 
from  the  edge  of  the  cap  over  the  exterior  of  the  glass.  The 
superabundance  is  easily  removed  by  a  knife,  and  the  an- 
nular surface  left  made  smooth  and  tight  by  a  hot  wire  passed 
rapidly  over  it.  If  a  piece  of  cement,  pushed  on  by  the 
edge  of  the  glass,  project  in  the  inside  of  the  cap,  it  should, 
when  nearly  cold,  be  cut  off  by  a  knife,  and  removed,  so 
that  no  loose  fragment  may  remain  in  the  retort  or  tube. 

835.  When  there  is  a  deficiency  of  apparatus,  and  caps  are 
wanting,  their  place  may  be  supplied  for  the  time  by  corks. 
Thus,  if  there  be  no  cap  large  enough  for  the  aperture  of  a 
jar  or  tube,  a  very  good  cork  may  be  selected,  made  to  fit 
tightly  into  the  aperture,  a  hole  pierced  through  it,  and  the 
cock  screwed  into  this  hole;  care  being  taken  that  the  cork  be 
not  divided  or  torn  to  pieces  by  the  force  applied.     This  may 
be  done  so  as  to  be  quite  tight,  or  if  a  small  leak  occur,  a  little 
soft  cement  (1125)  will  make  all  secure. 

836.  Connecters  are  short  perforated  pieces  of  metal,  tra- 
versed by  a  female  screw,  and  terminated  by  flat  surfaces  at 
the  ends,  so  as  to  screw  tightly  against  the  shoulders  of  stop- 
cocks (827).     They  have  on  their  extreme  surfaces  concentric 
grooves,  like  those  on  the  ends  of  retort  caps  (833),  to  meet 
and  hold  against  the  collars.  Their  use  is  to  connect  together 
stop-cocks  or  other  parts  of  apparatus  terminated  by  male 
screws,  and  hence  their  name.     They  are  best  made  square  on 
the  exterior,  being  then  more  firmly  held  in  the  hand,  or  by  a 
key,  when  tightly  screwed.     The  clean  state  of  the  worm,  of 
the  screw,  and  of  the  grooves,  should  be  attended  to  (833). 
The  want  of  these  connecters  may  at  times  be  supplied  by  a 
sound  perforated  cork  (835,  1331). 

837.  The  screws  of  all  these  stop-cocks,  caps,  and  con- 
necters, should  be  cut  with  the  same  thread,  so  as  readily  to 
fit  each  other;  several  of  each  should  be  ready  for  use,  and 
preserved  in  a  drawer  appropriated  to  the  purpose  (25);  those 
which  are  old  or  leaky  are  to  be  repaired  or  rejected,  and  the 
rest  kept  clean  and  in  good  order. 

838.  The  tightness  of  stop-cocks,  as  well  as  that  of  their 
junctions  with  connecters  and  caps,  and  also  of  caps  when 
cemented  upon  retorts,  may  be  determined  in  several  ways. 
If,  for  instance,  it  be  required  to  ascertain  whether  a  stop- 


TIGHTNESS  OF  STOP-COCKS  AND  CAPS.  383 

cock  is  tight,  it  may  be  screwed  to  the  plate  of  an  air-pump, 
and  the  pump  worked  until  the  guage  indicates  considerable 
exhaustion.  If,  without  further  working  of  the  pump,  this 
indication  continue  unaltered  for  some  time,  it  is  a  proof  that 
the  stop-cock  is  tight.  Or  the  cock  may  be  screwed  into  the 
top  of  a  capped  jar  (742)  standing  in  the  water-trough,  the 
water  raised  in  the  jar  to  near  the  top,  its  situation  mark- 
ed whilst  the  jar  stands  on  the  shelf,  and  then  again  after 
several  hours:  if  it  remain  unchanged  the  cock  is  tight.  Or 
a  still  simpler  method,  and  on  the  whole  a  very  good  one, 
is,  to  close  the  cock,  to  apply  one  end  to  the  mouth,  to  ex- 
haust the  air  within  the  small  cavity  as  much  as  possible  by 
the  mouth,  and  closing  the  aperture  by  the  lip  or  tongue,  to 
allow  it  to  be  forced  against  the  cock  by  the  pressure  of  the 
atmosphere.  If,  after  a  few  minutes,  the  adhesion  remains 
sensibly  undiminished,  it  is  a  proof  that  the  stop-cock  is 
sufficiently  tight  to  resist  the  passage  of  air  under  considera- 
ble pressure. 

839.  If  it  be  required  to  ascertain  whether  a  cap  has  been 
fixed  upon  a  retort,  so  as  to  be  quite  air-tight,  all  that  is  ne- 
cessary is  to  screw  in  a  stop-cock  before  ascertained  to  be 
secure,  to  attach  this  to  the  air-pump,  and  then  to  exhaust; 
if  the  gauge  remain  for  some  time  as  high  as  it  was  raised  by 
the  exhaustion,  all  is  tight,  or  if  it  fall,  air  finds  admission. 
The  same  trial  may  be  made,  though  not  so  rigorously,  by 
attaching  the  retort  and  stop-cock  to  a  transfer  or  capped  jar, 
nearly  filled  with  water,  and  standing  on  the  shelf  of  the 
pneumatic  trough,  and  then  opening  the  communication.  The 
level  of  the  water,  after  the  first  depression,  should  be  marked, 
and  if  it  fall  not  soon  afterwards,  it  is  a  proof  of  tightness 
under  pressures  equal  to  that  of  the  column  of  water  in  the  jar. 

840.  The  apertures  of  tubes  are  frequently  made  to  com- 
municate with  other  apertures  very  advantageously  by  con- 
necters  of  caoutchouc,   the  formation  and  application  of 
which  have  already  been  described  (449).     When  of  a  coni- 
cal shape,  they  connect  apertures  of  different  dimensions, 
conferring  great  flexibility  and  security  upon  the  apparatus 
(844). 

841.  Tubes  for  the  conducting  of  gas  and  vapour,  though 


384         CONNEXION  OF  TUBES — PAPER  TUBES. 

frequently  formed  of  rigid  materials,  as  glass,  metal,  or  por- 
celain, (699,  &c.)  are  also  sometimes  advantageously  con- 
structed of  flexible  substances.  Tubes  of  caoutchouc,  three 
or  four  feet  or  more  in  length,  are  easily  made  from  Han- 
cock's sheet  caoutchouc,  in  the  manner  already  described 
(449),  small  tubes  of  six  or  eight  inches  long  being  joined 
at  the  extremities,  by  surfaces  freshly  cut  with  a  clean  sharp 
knife.  Mr  Hancock  also  makes  flexible  air-tight  tubes  of 
any  length,  of  canvass  and  other  fabrics,  imbued  with  caout- 
chouc in  the  liquid  state:  similar  flexible  tubes  are  likewise 
manufactured  of  canvass  and  oil  boiled  with  litharge,  &c.* 

842.  It  may  be  useful  for  the  student  to  know,  that  very 
excellent  tubes  may  be  formed  of  pasted  paper,  sufficiently 
tight  to  be  serviceable  on  an  emergency  in  numerous  experi- 
ments upon  large  quantities  of  aeriform  substances,  such  as 
coal-gas,  fire-damp,  carbonic  acid,  &c.     They  should  be 
made  by  rolling  three  or  four  thicknesses  of  paper  round  a 
glass  tube,  a  rod,  or  a  wire,  one  half  of  the  paper  being  past- 
ed so  as  to  cause  at  least  the  two  outer  folds  to   adhere 
throughout.     If  after  they  are  made  they  be  brushed  over 
with  oil,  or  being  first  warmed,  with  melted  wax,  they  be- 
come very  tight.     A  tube  very  nearly  tight  enough  to  hold 
gas  under  small  pressures  may  be  made  simply  by  rolling  up 
smooth  writing  paper,  and  tying  it  round  with  thread.  When 
such  a  tube  is  wanted  for  the  conveyance  of  fluids,  the  paper 
may  be   first  oiled   or  waxed,  and  then  rolled  into   form 
(I337).f 

843.  When  tubes  are  used  for  the  ready  and  rapid  con- 
veyance of  gas,  it  is  desirable  that  they  should  be  of  suf- 
ficiently  large    dimensions.     No  difficulty  occurs  in    the 
usual  course  of  laboratory  experiments,  but  in  the  arts,  and 
sometimes  in  large  experiments  upon  the  transmission  of  gas, 
air,  or  steam,  much  annoyance  has  risen  from  the  contracted 
dimensions  of  the  tubes  employed. 

*  Very  convenient  flexible  tubes  are  made  of  lead.  Since  their  introduction 
by  Dr  Hare  into  chemical  use,  they  have  become  familiar  to  American  che- 
mists.—ED. 

t  Intestines  of  animals,  of  various  sizes,  cleansed,  inflated,  and  dried,  Yorm 
flexible  tubes,  accessible  in  most  situations,  and  very  easily  attached  by  common 
ligatures.— ED. 


SOLUTION  OF  GASES WOULFE*S  BOTTLES. 


385 


844.  In  numerous  cases  of  solution  or  chemical  action 
exerted  upon  or  by  gases,  there  is  occasion  to  pass  the  gas 
over  successive  portions  of  other  substances,  and  these,  when 
liquid,  are  best  placed  for  this  purpose  in  an  arrangement 
of  vessels  first  devised  by  Glauber,  but  which  with  some 
modifications  has  since  received  the  name  of  Woulfe's  appa- 
ratus (475,  959). 

In  the  general  arrangement,  a  series  of  close  vessels  are 
placed  side  by  side,  connected  by  tubes,  which  originating 
from  the  top  of  those  which  precede  in  the  series,  descend  to 

the  bottom  of  such  as  suc- 
ceed, as  in  the   delineated 
bottles  a,  6,  c,  and  the  tubes 
1,  2,  3.     The  gas   is  sup- 
posed to  be  delivered  into 
the  bottle  a,  by  the  tube  1. 
After  having  acted  upon  the  water  or  solution  there,  it  passes 
out  by  the  tube  2,  into  the  bottle  6,  and  from  thence  by  the 
third  tube  to  the  bottle  c.     Now  it  is  necessary  in  this  ar- 
rangement that  the  junctions  of  the  tubes  with  the  bottles  be 
air-tight,  or  the  pressure  exerted  upon  the  gas  by   the  fluid 
through  which  it  is  to  pass  will  cause  it  to  escape.     These 
junctions  are  made  in  various  ways.     The  tubes  may  some- 
times pass  through  corks,  and  be  tied  round  with  bladder, 
or  be  luted  (465,475,  1100,  &c.),  as  has  already  been  de- 
scribed; or  the  joints  may  be  ground  air-tight,  another  mode 
of  effecting  a  junction,  which  has  been  noticed  (475).     But 
these  and  similar  junctions  give  a  stiffness  and  rigidity  to  the 
whole  apparatus,  which  in  consequence  of  the  comparative 
slenderness  of  the  tubes,  and  the  size  and  weight  of  the 
parts  connected  by  them,  involves  considerable  risk  of  frac- 
ture to  the  former,  or  at  least  of  derangement  at  the  joints 
by  very  slight  shaking  or  motion  given  to  the  latter.  Hence 
it  is   desirable   to  have    flexible  or    moveable    junctions, 
and  this  is  well  effected  by  the  use  of  such  caoutchouc 
tubes  or  collars,  as  they  may  be  called,  as,  being  of  a  conical 
form,  may  be  tied  at  the  upper  edge  round  the  centre   tube, 
and  at  the  lower  round  thetubulature  (451),  as  is  represent- 
ed at  the  tubes  2  and  3,  bottle  b.     These  may  be  used  with 
2  Y 


386  WOULFE'S  BOTTLES — ^JUNCTIONS. 

most  gases,  chlorine  being  perhaps  the  only  one  likely  to  be 
passed  through  a  Woulfe's  apparatus  that  will  act  upon 
them. 

845.  Another  very  excellent,  though  more  expensive  mode 
of  forming  a  moveable  junction  is  represented  by  tube  3, 
bottle  c.     A  wide  tube  is  selected  and  fixed  air  tight,  either 
by  grinding  or  otherwise,  into  the  tubulature;  it  descends 
nearly  to  the  bottom,  and  is  cut  off  obliquely,  so  as  to  pre- 
sent an  oblique  aperture.     The  connecting  tube  3  is  made 
to  pass  down  this  tube,  and  having  its  end  turned  a  little  on 
one  side,  though  not  enough  to  prevent  its  being  easily 
drawn  up  and  down,  that  inclination  causes  the  gas  to  be 
thrown  off  laterally,  and  to  pass  under  the  edge  of  the  large 
tube,  and  through  the  solution,  into  the  space  above.     An 
arrangement  of  this  kind  is  rapidly  mounted  and  dismoun- 
ted ;   for  the  instant  the  conducting  tube  is  inserted  in  its 
place,  it  is  air-tight.    It  is  necessary,  in  all  such  arrange- 
ments, that  the  fluid  in  the  bottle  (c)  should  rise  above  the 
aperture  of  the  wide  tube,  and  that  the  extremity  of  the  con- 
ducting tube  should  descend  below  it. 

846.  Considering  the  joints  as  being  properly  made  in  any 
of  these  methods,  let  us  illustrate  the  uses  of  the  arrange- 
ment by  supposing  muriatic  acid  gas  to  be  thrown  into  the 
apparatus  by  tube  1 ;  it  will  pass  into  the  water,  and  be  im- 
mediately dissolved ;  but  as  from  the  continual  additions  of 
fresh  gas  the  liquid  becomes  saturated,  a  part  of  the  gas 
will  pass  into  the  upper  part  of  the  bottle,  and  propelling 
the  air  before  it,  will  enter  the  bottle  b  by  tube  2.     Here  it 
will  operate  exactly  as  in  the  first  bottle  a,  if  the  arrange- 
ment be  the  same  and  the  gas  be  conducted  into  the  fluid: 
but  if,  as  in  the  figure,  this  be  not  the  case,  it  will,  after  ac- 
ting upon  and  saturating  the  fluid  as  much  as  practicable  by 
the  surface,  pass  on  in  a  similar  manner  to  the  third  bottle, 
and  from  that  to  wherever  the  fourth  tube  may  lead. 

847.  Such  is  the  simple  operation ;  but  it  is  liable  to  fre- 
quent variations,  which  are  to  be  met  by  particular  con- 
trivances.    Amongst  the  most  essential  of  these  is  the  appli- 
cation of  safety-tubes,  intended  to  admit  air  when,  from  any 
cause,  the  pressure  within  is  so-  far  diminished  as  to  be  con- 


WdULFE's  BOTTLES SAFETY-TUBES WATER.  387 

siderably  less  than  that  of  the  atmosphere.  Suppose  for  in- 
stance that  the  currents  of  gas  into  the  bottles  a  and  6  were 
stopped  while  solution  was  still  going  on  :  as  the  water  dis- 
solved the  gas  above  it,  the  atmospheric  pressure  would 
force  the  fluid  from  the  bottle  c  up  the  third  tube  into  the 
bottle  &,  and  if  it  reached  the  aperture  of  the  second  tube, 
even  in  part  into  the  bottle  a.  If  the  operation  had  occa- 
sioned the  evolution  of  heat,  a  mere  depression  of  tempera- 
ture within  the  bottle  might  produce  the  same  effect,  and 
in  this  manner  cause  great  derangement  of  the  liquid  and  the 
failure  of  the  experiment. 

848.  All   this  may  be  avoided  by  the  use  of  the  small 
safety-tube  d,  first  applied  by  M.  Lavoisier  from  an  idea 
suggested  by  M.  Hassenfratz*.     It  passes  through  a  tight 
joint  into  the  bottle,  and  has  its  lower  extremity  immersed 
in  the  liquid  to  the  depth  of  half  an  inch  or  more.     When 
the  absorption  before  described  takes  place,  air  passes  down 
the  tube,  enters  the  bottle,  and  prevents  the  recession  of  the 
•liquid  from  the  other  bottles.     No  air  can  at  any  time  es- 
cape there,  but  any  pressure  exerted  from  within  outward 
is  indicated,  and  even  measured,  by  the  elevation  of  a  col- 
umn of  fluid  in  the  tube :  in  this  way  such  tubes  are  highly 
useful  in  shewing  the  state  of  things  within.     Another  tube 
of  safety  called  Welter's  has  been  already  described  (478), 
which,  being  fixed  into  the  middle  tubulature  of  the  bottle, 
will  render  that  just  mentioned  needless. 

849.  When  the  bottles  are  connected  in  the  manner  de- 
scribed (845  tube  3,  bottle  c,)  by  a  fixed  tube,  the  latter 
becomes  a  tube  of  safety,  permitting  the  entrance  of  air  when- 
ever the  external  pressure  is  much  above  that  within. 

850.  On  first  setting  an  apparatus  of  this  kind  to  work,  the 
student  should  be  attentive  to  the  quantity  of  water  in  the 
bottles,  and  the  depth  to  which  the  extremities  of  the  con- 
necting tubes  are  immersed.     Supposing  the  immersion  to  be 
two  inches  in  each  of  the  bottles  a  and  c,  it  makes  a  pressure 
of  four  inches,  which  has  to  be  overcome  by  the  gas  passing 
into  the  apparatus  through  the  first  tube.     From  inattention, 
this  pressure  may  be  very  considerably  increased,  and  to  such 

*  Tiaite  Elementaire  de  Chimie,  453. 


388          WOULFE'S  BOTTLES — KNIGHT'S  SUGGESTION. 

an  extent  astointerfere  with  the  arrangement  of  the  apparatus 
in  which  the  gas  is  evolved;  in  consequence  of  which,  lutings 
may  be  deranged,  and  even  the  vessels  burst.  Hence  as  a 
general  rule,  the  conducting  tubes  are  not  to  be  immersed 
more  than  is  needful. 

851.  Upon  numerous  occasions  it  is  not  necessary  to 
immerse  the  tubes  at  all,  especially  in  the  large  way;  conse- 
quently, apparatus  may  then  be  used  for  the  liberation  of  the 
gas,  which  would  be  quite  inadmissiblawere  any  pressure  to 
be  exerted  within  it.     This  is  particularly  the  case  with  mu- 
riatic acid,  for  the  solution  formed  by  that  gas  in  water  being 
heavier  than  either  the  water  or  weaker  solution  beneath  it, 
falls  to  the  bottom.    Hence  in  a  muriatic  acid  gas  arrange- 
ment, the  delivering  tube  may^erminate  above  the  surface  of 
the  water  as  in  bottle  b;  the  water,  as  it  dissolves  the  gas, 
will  descend,  and  this  change  of  place  will  go  on  until  it  be 
fully  saturated.     On  the  contrary,  with  ammonia  the  reverse 
is  the  case,  the  solution  of  that  substance  being  lighter  than 
water;  it  is  essential  therefore  that  this  gas  be  delivered  at  the1 
bottom  of  the  bottle,  that  it  may  always  come  first  into  con- 
tact with  the  weakest  portions  of  solution. 

852.  In  several  cases  the  gas  is  conducted  to  the  bottom 
of  the  fluid,  that  the  bubbles  in  their  ascent  may  cause  agi- 
tation, and  thus  favour  the  solution.     This  is  necessary  in 
dissolving  chlorine  in  water,  and  is  advantageous  with  am- 
moniacal  and  sulphurous  acid  gases. 

853.  Although  three  bottles  are  figured  in  the  wood-cut, 
often  not  more  than  one  is  required  at  a  time,  and  the  two  or 
three  tubes,  in  place  of  being  passed  each  through  a  separate 
tubulature,  may  be  put  through  three  holes  in  a  cork  adapted 
to  the  mouth  of  an  ordinary  bottle;  and  the  junction  be  made 
good  by  soft  cement  or  other  means.     A  wide-mouthed  jar, 
or  bottle,  will  occasionally  make  a  very  good  Woulfe's  appa- 
ratus; and  a  large  stone  bottle  often  answers  the  same  purpose 
even  in  chemical  manufactories. 

854.  Dr  Knight  of  Aberdeen  avoids  much  of  the  trouble 
resulting  from  a  stiff  Woulfe's  apparatus,  by  supporting  the 
differentbottles  each  on  sand,  placed  in  a  bowl  or  cup  of  com- 
mon stone  ware.     That  quantity  of  motion  is  then  allowed 
which  is  sufficient  to  compensate  for  the  casual  alteration  of 


NOOTH'S  APPARATUS SOLUTION  OF  CHLORINE*  389 

the  position  of  the  parts;  the^tubes  are  saved  from  injury,  and 
the  whole  works  well  and  pleasantly. 

855.  An  apparatus  invented  by  the  late  Dr  Nooth,  and 
distinguished  by  his  name,  is  occasionally  used  for  the  purpose 
of  making  a  solution  of  carbonic  acid.     It  is  rather  compli- 
cated, is  of  no  general  use  in  the  laboratory,  and  does  not 
require    particular   description;  but   it  may  be  prudent  to 
caution  those  who  possess  it,  against  generating  gas  afresh  in 
the  lower  vessel  without  first  ascertaining  that    the  valve 
between  that  and  the  second  is  in  right  order.     This  is  easily 
done  by  lifting  the  upper  vessel  from  the  lower,  raising  it  over 
the  head,  and  applying  the  mouth  to  the  lower  aperture  of  the 
valve  tube;  if  the  muscles  of  the  cheeks  have  not  power  to 
raise  this  valve  and  blow  air  through  it,  the  apparatus  should 
not  be  used.     The  valve  is  always  out  of  order  when  it  cannot 
thus  be  raised;  and  from  inattention  to  this  circumstance, 
apparatus  of  the  kind  has,  in  two  or  three  cases,  been  blown 
to  pieces. 

856.  Solutions  of  muriatic  acid,  ammonia,  and  sulphurous 
acid,  are  generally  retained  upon  the  shelves.     Solution  of 
chlorine  is  often  wanted,  but  is  not  usually  preserved.     It  is 
readily  formed  by  opening  a  bottle  of  chlorine  (824)  in  an 
inverted  position  underwater,  allowing  a  little  of  the  fluid  to 
enter,  replacing  the  stopper,  and  then  agitating  the  contents  of 
the  vessel;  in  a  second  or  two  it  is  again  to  be  opened  under 
water,  when  more  of  the  fluid  will  enter;  it  is  then  to  be  re- 
stopped  and  re-agitated,  fresh  water  admitted,  and  the  process 
thus  continued  until  the  bottle  is  half  full.     By  further  agita- 
tion, nearly  all  the  gas  may  be  taken  up  by  this  quantity  of 
water,  but  air  should  be  admitted  now  and  then  to  supply  the 
place  of  the  gas  dissolved.     In  opening  the  bottle,   either 
under  water  or  in  the  air,  the  stopper  is  not  to  be  removed 
farther  than  just  sufficient  to  allow  the  ingress  of  the  air  or 
water,  otherwise  loss  of  the  solution  or   of  the  gas  is   occa- 
sioned. 

857.  Before  leaving  the  description  of  those  operations 
which  relate    directly  to  the  transference  and  removal  of 
gases,  it  will  be  proper  to  observe  that,  although  in  making 
mixtures  of  gases  they  will   become  uniform  without  agita- 


390  GASES  MIXED AIR-PUMP,  &,C. 

tion  if  sufficient  time  be  allowed,  the  period  required  will 
be' very  long,  extending  even  to  hours,  in  narrow  vessels. 
If  hydrogen  be  thrown  up  into  a  wide  jar  half  full  of  ox- 
ygen, so  as  to  fill  it,  snd  no  further  agitation  be  given,  the 
mixture,  after  a  lapse  of  several  minutes,  will  be  of  different 
composition  above  and  below.  Hence  the  propriety  in  all 
cases  of  mixture,  of  agitating  the  gases  well  together.  This 
precaution  is  more  particularly  necessary  inUhose  eudiomet- 
rical  or  analytical  processes,  which  require  the  mixture  of 
gasesTn  tubes  or  narrow  vessels. 

§'  6.  Jlir-pumps,  Syringes,  and  the  operations  performed 
with  them. 


858.  Air-pumps  and  syringes  are  instruments  of  great  ser- 
vice and  constant  use  in  the  laboratory,  but  are  in  their  con- 
struction and  reparation  so  necessarily  the  work  of  the  in- 
strument-maker, as  to  render  needless  here  every  thing  rela- 
tive to  these  points.     The  air-pump  is  required  not  merely 
in  the  exhaustion  of  receivers  for  experiments  with  atmos- 
pheres of  less  pressure  than  those  ordinarily  occurring,  but 
also  for  the  removal  of  air  from  retorts,  flasks,  globes,  &c., 
that  other  gaseous  bodies  may  be  introduced.     A  good  sy- 
ringe, will  answer  the  same  purpose  to  a  very  considerable 
extent,  when  the  air-pump  is  absent.     It  has  the  great  ad- 
vantage of  combining  the  power  of  condensing  air  (822) 
with  that  of  exhausting  it,  at  a  very  little  additional  expense. 
All  the  screws  by  which  the  attachment  of  other  apparatus 
to  the  pump  or  syringe  is  to  be  effected,  should  be  cut  with 
the  same  thread  as  that  adopted  for  the  stop-cocks  (742,  804, 
810,  827),  that  the    screws  thus  used   may  fit  each  other 
without  difficulty. 

859.  The  student  has  to  observe  that  the  pistons  of  these 
instruments  are  well  oiled,  move  easily  and  tightly,  and  that 
all  the  fixed  joints  are  so  perfect,  as  to  prevent  leakage  of 
air  at  any  of  the  screws  or  junctions.     The  tightness  of  the 
pump  is  easily  ascertained  by  screwing  a  stop-cock  into  the 
air  aperture  upon  the  plate,  closing  it,  and  then  working 
the  pump  until  the  gauge  indicates  considerable  exhaustion. 


AIHrPUMP SYRINGE-— TIGHTNESS.  o9  1 

4* 

WHen  the  pistons  are  in  order,  the  experimenter  feels  as  he 
moves  the  handle,  that  he  withdraws  air  each  time  a  piston 
rises,  and  he  Can  also  perceive  without  difficulty  that  less 
and  less  is  removed  at  each  successive  stroke.  The  diminu- 
tion should  proceed  until  none  can  be  withdrawn  by  further 
operations;  and  this  useless  condition  of  the  piston  when  at 
work,  which  is  judged  of  by  the  hand  (862),  should  coincide 
with  the  stationary  and  highest  state  of  the  gauge,  indicative 
of  the  exhaustion  within.  If  after  some  time  the  gauge  con- 
tinues to  indicate  the  same  exhaustion,  it  is  a  proof  that  no 
air  can  pass  into  a  receiver  fixed  tightly  upoii  a  plate  and 
similarly  exhausted  ;  and  if  upon  working  the  pistons,  the 
same  absence  of  air  is  indicated  beneath  them  as  when 
the  exhaustion  was  first  effected,  it  is  a  proof  that  no  air  pas- 
ses by  them  into  the  lower  part  of  the  pump  cylinders. 

860.  The  plate  of  an  air-pump  should  be  perfectly  flat, 
and  ground  so  smooth  that  a  little  pomatum  may  render  a 
receiver  with  ground  edges  quite  tight  when  placed  upon 
it.     It  should  be  secured  from  injury  by  a  tin  cover  put 
over  it  at  all  times  when  not  required  for  experiment ;  for 
very   slight    blows   with  hard  substances    produce   serious 
harm  by  the  depressions  they  occasion. 

861.  The  tightness  of  a  syringe  piston,  when  its   other 
parts  are  accurately  fitted,  may  be  judged  of  by  drawing  the 
piston  as  far  back  as  possible,  then  closing  either  the  ex- 
hausting or  condensing  aperture  by  a  stop-cock,  carrying 
the  piston  forward  to  the  end  of  the  cylinder,  if  that  may 
be  done,    and  retaining  it  there  a  minute   or    two.      This 
motion  condenses  the  air  before  the  piston,  and  rarefies  that 
behind  it ;  and  if  the  piston  be  not  quite  tight,  the  air  will 
pass  it,  whilst  it  is  forcibly  held  forward,  and  consequently 
when  the  hand  is  removed,  the  piston  will  not  return,  as 
it  ought,  to  the  top  of  the  cylinder,  or  to  the  place  from 
whence  it  was  displaced.     If  there  be  leaks  at  the  joints 
of  the  syringe,  then  the   effect  above    described  may   be 
produced,  although    the  piston  be   tight.      In  either  case 
the   imperfection    of  the  instrument   is    ascertained,    and 
it  should  be  sent  to    a  workman  to  be  repaired. 

862.  A  syringe  has  not  the  advantage  of  an  attached  gauge 


I 

• 


392  AIR-PUMP,  &C. PRESERVED. 

like  that  of  the  pump,  hence  exhaustions  made  by  it  are  ne- 
cessarily judged  of  by  the  feel  of  the  piston  when  in  motion. 
As  soon  as  the  quantity  of  air  removed  at  each  stroke  has 
diminished  to  nothing,  the  exhaustion  is  as  complete  as  possi- 
ble. This  indication  is  the  same  as  that  already  described 
with  the  air-pump  (859),  but  may  be  more  distinctly  ex- 
plained in  consequence  of  one  piston  only  being  in  action. 
It  depends,  generally,  upon  the  effort  made  by  the  air  to  lift 
and  pass  through  the  valve  in  the  piston,  as  the  latter  pres- 
ses upon  it.  On  first  working  the  syringe,  this  happens  im- 
mediately the  piston  is  advanced ;  but  as  the  air  is  more  and 
more  rarefied  by  exhaustion,  the  piston  has  to  descend  further 
and  further,  before  the  portion  in  the  cylinder  beneath  is 
sufficiently  compressed  to  lift  and  pass  the  valve.  It  is  the 
particular  effect  of  lifting  the  valve  which,  becoming  sen- 
sible to  the  hand  in  ordinary  air-pumps  and  syringes,  sup- 
plies the  indication  in  question  ;  this  is  easily  felt  and  ob- 
served, but  difficult  clearly  to  describe. 

863.  When  the  instrument  is  absolutely  bad,  and  cannot 
be  replaced  or  repaired,  the  student  must  compensate  for  the 
imperfections  ^as  far  as  he  can,  by  interposing  a  stop-cock 
between  it  and  the  retort,  flask,  or  other  vessel  (which  in- 
deed in  most  experiments  of  this  kind  is  necessary  for  other 
reasons),  and  close  the  communication  as  soon  as,  by  rapidly 
working  the  instrument,  he  has  effected  the  best  exhaustion 
he  can  attain. 

864.  Air-pumps  and  syringes  should  be  preserved  from 
injury,  likely  to  arise  from  mechanical  violence  or  chemical 
action.     They  are  best  secured,  not  in  the  laboratory,  but  in 
the  place  appropriated  to  the  balance  (29),  and  other  appa- 
ratus, liable  to  injury  from  acid  fumes.     And  if  in  cases  of 
emergency  any  gas  has  been  passed  through  them,  which 
exerts  the  slightest  action  on  the  metal,  leather,  silk,  or  oil, 
the  instrument  should  be  quickly  worked  in  the  air,  as  soon 
as  it  can  be  liberated  from  the  experiment,  that  the  injury 
may,  if  possible,  be  prevented  by  the  instant  removal  of  all 
the  gas ;  or  it  should  be  immediately  dismounted  and  cleaned. 

865.  The  oiled  silk  valve  generally  applied  in  these  in- 
struments is  exceedingly  simpfe  in  construction,  buf  liable 


i 

, 


SILK-VALVE EXHAUSTED   VESSELS.  393 

to  go  out  of  repair  quickly,  especially  if  certain  gases  or  va- 
pours have  passed  it;  on  the  other  hand  it  is  repaired  with 
great  facility,  and  its  description  may,  therefore,  be  useful. 
It  consists  of  an  aperture  of  small  diameter  made  in  a  part 
of  the  metal  of  the  piston  or  of  the  extremity  of  the  barrel, 
the  aperture  terminating  on  a  flat  surface  ;  a  strip  of  silk  is  put 
over  this  surface,  and  the  aperture  and  its  ends  being  pass- 
ed down  the  sides  of  the  metal,  a  turn  or  two  of  thread  is  ta- 
ken round  them,  which  confines  the  strip  to  its  proper  place. 
As  the  air  or  gas  passes  through  the  hole  against  the  silk,  it 
easily  escapes  under  its  edges,  but  as  the  air  tends  to  proceed 
in  the  opposite  direction,  it  presses  the  silk  slip  against  the 
aperture,  and  stops  all  passage.  When  the  valve  is  out  of 
order  from  the  derangement  of  the  silk,  nothing  is  more  easy 
than  to  remove  the  latter  and  tie  another  slip  in  its  place. 

860.  The  pressure  upon  the  exterior  of  vessels  exhausted 
of  air  is  about  15lbs.  upon  every  square  inch  of  their  sur- 
face, and  with  large  vessels  it  accumulates  to  an  enormous 
extent.  For  this  reason  the  form  of  such  as  are  intended  to 
sustain  this  pressure  must  be  particularly  attended  to,  espe- 
cially when,  as  in  usual  laboratory  operations,  they  are  of 
glass.  Air-pump  receivers  are  always  made  of  curved  forms, 
and  particular  directions  have  already  been  given  with  re- 
gard to  the  proper  form  of  retorts  (429)  which  are  to  be  ex- 
hausted. A  retort  is  so  convenient  for  the  retention  of  solid 
or  fluid  matter  during  exhaustions;  for  the  reception  of  suffi- 
cient gaseous  matter  to  act  upon  the  substances  within ;  for 
its  allowing  the  heating  of  the  substances  in  the  gas  even 
whilst  on  the  air-pump,  and  for  the  opportunity  it  affords  of 
viewing  all  that  passes;  that  it  is  in  constant  request  in  ex- 
periments of  this  kind,  where  gaseous  bodies  are  acting  on 
each  other,  or  on  fluids  or  solids  (429).  Well-formed  flasks 
and  globes  are  also  in  constant  use,  as  bearing  exhaustion, 
and  readily  allowing  the  mixture  of  gases  in  them :  a  com- 
mon Florence  flask  (373)  will,  from  the  general  perfection 
of  its  form,  sustain  perfect  exhaustion,  notwithstanding  its 
thinness;  and  these,  with  globes  and  retorts,  are  easily  at- 
tached to  the  pump  or  syringe  by  means  of  caps  and  stop- 
cocks (827). 
2  Z 


394  VESSELS  EXHAUSTED PRECAUTIONS. 

867.  Particular  care  is  necessary  with  all  exhausted  glass 
vessels,  that  no  sudden  blow,  even  though  slight,  take  place 
on  the  exterior,  especially  with  sharp  edged  or  hard  sub- 
stances, for  the  slightest  fracture  of  the  surface  leads  to  the 
destruction  of  the  whole.     A  retort,  flask  or  globe  may  be 
destroyed  merely  by  laying  it  down  hastily  upon  a  table, 
especially  if  a  particle  of  sand  or  any  other  hard  substance 
be  beneath  it;  and  a  slight  blow  with  a  glass  rod  or  metal 
wire,  which  would  do  no  harm  to  the  apparatus  in  its  usual 
state,  will  now  shiver  it  to  pieces. 

868.  On   exhausting  glass  vessels  for  the  first  time,  they 
should,  after  being  attached  to  the  pump  or  syringe,  be  co- 
vered with  a  cloth,  before  the  exhaustion  is  effected.   If  they 
burst  by  the  mere  pressure  of  the  external  atmosphere,  the 
fragments  are  then  prevented  from  flying  to  any  distance. 
Pieces  which  may  have  fallen  upon  the  plate  fcf  the  pump, 
or  have  entered  into  the  stop-cock  by  which  the  vessels  has 
been  attached,  are  to  be  carefully  and  immediately  removed, 
that  no  injury  may  be  caused  by  them  to  the  ground  metallic 
surfaces,  or  to  other  parts. 

869.  The  general  process  for  removing  the  air  from  a 
vessel,  and  for  replacing  it  by  any  required  gas,  is  an  easy 
one,  and  will  be  readily  understood  from  description.     The 
gas  is  to  be  collected  in  a  transfer  jar  (755),  over  water  or 
mercury,  according  to  its  nature,  and  a  connecter  screwed 
to  the  upper  end  of  the  jar  stop-cock.     The  vessel  to  be  ex- 
hausted must  have  a  cap  fitted  securely  to  its  neck  (833), 
and  a  stop-cock  screwed  into  the  cap,  and  then,   being  at- 
tached by  means  of  the  cock  to  the  air-pump  or  syringe,  it  is 
to  be  exhausted,  and  the  cock  closed.     This  done,  the  vessel 
is  to  be  separated  from  the  pump  and  attached  to  the  jar  by 
means  of  the  connecter,  the  stop-cock  of  the  jar  being  screwed 
tightly  into  it ;  the  lower  of  the  two  cocks,  which  now  in- 
tervenes between  the  jar  and  the  exhausted  vessel,  is  to 
be  opened;  then  the  upper  one  gradually,  and  the  gas  slowly 
admitted,  until  the  vessel  be  full,  or  sufficient  has  passed  in. 

870.  If  the  volume  of  gas  which  enters  is  to  be  ascertained, 
it  will  be  necessary  to  equalize  the  level  within  and  without 
the  jar  (767),  but  this  must  not  be  done  until  the  tempera- 


\ 
VESSELS  FILLED   WITH  GAS.  395 

ture  within  the  globe  is  the  same  as  that  of  the  surrounding 
air.  When  air  rushes  into  an  exhausted  vessel,  it  first  occa- 
sions a  depression  of  the  temperature  within,  but  afterwards 
an  elevation  (effects  dependant  upon  well  known  causes). 
To  prevent  therefore  the  interference  of  any  accidental  tem- 
perature thus  produced,  the  level  within  and  without  is  to  be 
equalized,  the  stop-cock  shut,  and  the  apparatus  left  for  a 
few  minutes ;  afterwards  the  level  is  again  to  be  equalized, 
the  stop-cock  opened,  and  at  the  same  time  the  surface  of 
the  water  in  the  jar  observed  ;  its  motion  indicates  that  the 
temperature  within  has  changed:  again,  the  vessel  must  be 
closed,  left  for  a  time,  and  then  examined,  and  when  after 
the  lapse  of  five  minutes  no  change  in  the  level  is  produced 
by  opening  the  stop-cock,  it  is  a  proof  that  the  temperature 
within  is  the  same  as  that  of  the  atmosphere.  This  done, 
the  stop-cocks  are  to  be  finally  closed,  and  the  retort  or 
vessel  removed  and  used  as  the  experiment  may  require. 

871.  It  sometimes  happens  that  when  the  gas  to  be  intro- 
duced has  been  collected  over  water,  a  drop  or  two  of  that 
fluid  adheres  near  the  upper  aperture,  and,  if  the  gas  be 
allowed  to  pass  with  violence,  is  carried   forward  into  the 
exhausted  vessel  by  the  current.     Care  should  be  taken  to 
prevent  this,  for  which  reason,  in  addition  to  other  precau- 
tions, it  is  useful  to  introduce  a  little  piece  of  crumbled  fil- 
tering paper  into  the  top  of  the  connecter,  so  that  when  the 
second  stop-cock  is  screwed  into  its  place,  the  paper  may 
lie  loosely  between  the  apertures  of  the  two.     It  will  catch 
any  drops  of  water  that  may  be  carried  up,  and  prevent  their 
entrance  into  or  beyond  the  second  stop-cock. 

872.  The  general  process  of  the  introduction  of  gases  con- 
nected with  the  use  of  the  air-pump  is  required  in  the  weigh- 
ing of  gases;  in  the  mixing  of  those  which  are   affected  by 
water  or  mercury,  or  afford  results  so  affected;  and  in  the  ex- 
posure of  particular  substances  to  gases  or  vapours.     Where, 
however,  actions  of  the  latter  kind  are  exerted  spontaneously, 
as  is  often  the  case  with  chlorine,  it  is  frequently  sufficient 
to  put  the  substance  into  a  tube  closed  at  one  end,  and 
having  opened  a  small  bottle  of  chlorine,  quickly  to  introduce 
the  tube  and  close  the  bottle.    Substances  are  also  very 


396  VESSELS  FILLED  BY  COMPRESSION. 

often  advantageously  exposed  to  gases  in  tubes  in  the  manner 
already  described  (698,  &c). 

873.  With  regard  to  those  operations  in  which  the  com- 
pression of  gases,  instead  of  their  expansion  and  exhaustion, 
is  required,  they  are  performed  by  means  of  the  syringe  al- 
ready spoken  of  (858,  &c.);  but  the  vessel  is  now  to  be  screw- 
ed to  the  end  from  which  the  gas  is  to  be  forced  out,  and  the 
opposite  aperture  is  to  be  connected  by  a  tube,  or  otherwise, 
with  a  gasometer,  or  other  vessel  containing  the  gas.     When 
the  syringe  is  worked,  it  draws  the  air  out  of  the  latter  vessel* 
and  forces  it  into  the  former.     Suppose  the  operation  were 
to  condense  oxygen  to  the  amount  of  four  or  five  atmospheres 
into  a  brass  globe,  for  the  purpose  of  making  a  blow-pipe 
(252);  the  globe  is  first  to  be  attached  to  the  syringe,  and  to 
have  the  air  exhausted  from  it;  then  to  be  detached,  and  the 
same   aperture  of  the  syringe  connected   with  the  vessel, 
which  is  to  supply  oxygen  gas.     It  is  now  necessary  to  expel 
the  air  contained  in  the  syringe  and  pipe;  one  stroke  of  the 
piston  is  sufficient  to  remove  that  in  the  syringe,  and  a  second 
will  generally  expel  all  that  was  contained  in   the  pipes,   if 
they  be  of  moderate  size.     The  exhausted  globe  is  then  to  be 
attached  to  the  exit  aperture  of  the  syringe,  and  all  the  cocks 
being  opened  oxygen  will  immediately  pass  into   the  globe, 
and  fill  it  nearly  to  atmospheric  pressure;  the  piston  is  then 
to  be  worked,  and  as  much  more  oxygen  thrown  in  as  may 
be  required;  finally,  the  stop-cocks  are  to  be  closed,  and  the 
apparatus  dismounted.     The    quantity  of   gas    introduced 
may  be  judged  of  by  that  which  has  disappeared  from  the 
jar  or  vessel,  if  it  be  visible  and  can  be  appreciated. 

874.  Retorts  and  flasks  will  not  bear  so  great  a  pressure 
on  their  interior  as  on  their  exterior,  and  many  that  will  bear 
exhaustion  with  perfect  safety,  will  burst  long  before  they 
have  received  one  additional  atmosphere.     Even  the  force  of 
the  mouth  is  adequate  to  the  bursting  of  thin  Florence  flasks. 
Hence  the  glass  vessels  intended  to  retain  gases  under  pres- 
sure must  be  thick,  or  of  small  diameter.     Small  globes  are 
useful  in  such  experiments,  and  also  small  tubes  carefully 
closed  at  one  end,  and  well  annealed.     According  to  some 
experiments  of  Mr  Brunnell,  a  uniform  flint  glass  tube,  its 


CORRECTION  OF  THE  VOLUME  OF  GASES.         397 

thickness  being  ten,  and  its  internal  diameter  eighteen,  sus- 
tained an  internal  pressure  of  135  atmospheres  of  14  Ibs. 
each,  when  applied  in  a  regular  and  careful  manner.  Hence 
the  strength  of  other  glass  tubes  may  easily  be  calculated 
by  the  rule  of  proportion,  for  if  the  glass  be  but  one  half 
this  thickness,  it  will  resist  only  half  that  number  of  atmo- 
spheres. No  force  should  be  exerted  in  experiments  surpass- 
ing one  third,  or  at  most  one  half  of  the  calculated  strength; 
and,  indeed,  it  is  rarely  that  glass  tubes  are  so  uniform  in 
structure  or  so  well  annealed  as  to  have  near  the  strength 
indicated  in  the  above  experiment. 

875.  When  small  globes  or  tubes  are  fitted  with  caps  for 
the  purpose  of  connecting  them  with  a  syringe,  in  order  to 
subject  them  to  internal  pressure,  it  is  necessary  that  partic- 
ular care  be  taken  in  fastening  on  the   cap  that  it  may  re- 
main tight  and  firm.     The  outside  of  the  neck  should  in 
such  cases  be  roughened  by  a  file,  and  the  junction  of  it  with 
the  inside  of  the  cap  by  cement  very  carefully  and  ^accu- 
rately  made  (833).     Cement  so  warm  as  to  be  in  a  state  of 
thick  fluidity  should  afterwards  be  put  over  the  outside  of  the 
cap  and  the  glass  beyond,  and  drawn-out  tow  wound  round  it, 
so  as  to  pass  obliquely  backwards  and  forwards  from  the 
glass  to  the  cap,  and  back  upon  the  glass  again.     This  should 
be  covered  entirely  by  more  cement,  and  will  help  much 
to  bind  the  vessel  and  cap  together.     At  other  times  a  band 
of  thin  open  canvass  may  in  the  same  manner  be  buried  in 
the  cement,  passing  once  or  twice  round  the  joint;  or  cloth 
or  thick  muslin  may   be   used  for  the  same   purpose;    but 
whatever  it  is,  it  should  be  thoroughly  soaked  in,  and  com- 
pletely covered  by,  the  cement. 

§7.  Correction  of  the  Volume  of  Gases  for  Temperature, 
and  Pressure. 

876.  In  all  the  processes  relative  to  volumes  of  gases, 
directions  have  been  given  that  the  temperature  and  the  baro- 
metric pressure  be  noted  at  the  time   (781,  888),      This  is 
for  the  purpose  of  making  such  corrections  as  shall  enable 
the  operator  to  compare   the  results  obtained  at  one   time 


398  CORRECTION  FOR  TEMPERATURE. 

with  those  obtained  at  another.  When  the  temperatures  of 
gases  have  been  raised  whilst  the  pressure  upon  them 
remains  the  same,  they  expand  in  bulk;  and  when  their 
temperatures  are  lowered,  they  contract,  but  the  bulk  is 
determinate  for  every  temperature.  On  the  other  hand,  if  the 
temperature  be  constant  when  the  pressure  is  varied,  then 
variations  in  bulk  are  also  occasioned,  the  volume  increasing 
as  the  pressure  is  diminished,  and  decreasing  as  it  is  in- 
creased, whilst  it  still  remains  constant  and  determinate 
for  every  particular  degree  of  force  so  applied.  Now  as 
atmospheric  temperature  and  pressure  vary  continually,  it  is 
evident  that  experiments  made  at  different  times  must,  oc- 
casionally, differ  as  to  the  volume  of  gas  they  require,  and, 
consequently,  it  would  be  inaccurate  to  compare  these  dif- 
ferent volumes  without  ascertaining  the  influence  of  tem- 
perature and  pressure  upon  them;  the  latter  must,  therefore, 
be  observed  and  registered.  This  being  done,  it  is  easy  to 
apply  corrections  by  which  the  volume  of  gas  used  at  any 
one  time  can  be  truly  compared  to  that  used  at  another;  for 
as  the  bulk  is  determinate  for  any  given  temperature  and 
pressure,  it  is  only  necessary  to  correct  the  bulk  of  the  one 
portion  to  the  temperature  and  pressure  of  the  other,  or  to 
select  two  fixed  points  of  this  kind,  and  in  every  case  to  re- 
duce the  observed  volume  of  gas  to  what  it  would  be  at  these 
points ;  the  results  will  then  be  perfectly  consistent. 

877.  The  points  usually  adopted  in  this  country,  and  dis- 
tinguished as  mean  temperature  and  pressure,  are  for  tempe- 
rature 60°  of  Fahrenheit's  scale,  and  for  pressure  30  inches  of 
mercury.     Hence,  when  necessary,  gas  observed  at  any  other 
temperature  and  pressure  has  to  be  reduced  to  the  volume 
it  would  occupy  at  these  points.    This  may  be  done  in  the 
following  manner  : 

Correction  for  Temperature. 

878.  It  appears  by  the  experiments  of  MM.  Gay  Lussac 
and  Dalton,  that  all  gases  and  vapours  of  whatever  nature, 
when  not  in  contact  with  liquids,  are  affected  equally  in  their 
volume  by  changes  of  temperature,  the  increase  in  volume 


CORRECTION  FOR  TEMPERATURE.  399 

for  every  additional  degree  of  heat  of  Fahrenheit's  scale  being 
_i^.  part  of  the  volume  at  32°  Fahrenheit,  and  the  decrease 
for  every  diminution  of  temperature  of  one  degree  being  also 
_|^  part  of  the  volume  at  32°  Fahrenheit.  This  known,  it 
is  easy  to  calculate  how  much  a  volume  of  gas  at  a  given  tem- 
perature, 60°  Fahrenheit,  for  instance,  would  be  increased  or 
diminished  by  a  change  of  one  or  more  degrees.  For  though 
it  is  not  for  one  degree,  a  ^  part  of  the  bulk  at  60°,  the  pro- 
portion is  easily  ascertained  by  adding  28,  or  the  number 
of  degrees  of  the  observed  gas  above  32°  to  480,  which 
producing  508,  indicates  that  7^¥  part  of  the  bulk  at  60°  is 
to  be  considered  as  the  increase  or  diminution  for  every  de- 
gree of  change.  For  conceive  480  parts  of  gas  at  32°:  at  33° 
they  become  481  parts;  at  34°,  482  parts;  at  60°,  508  parts; 
the  increase  at  each  degree  being  T|0  of  the  volume  at  32°, 
and,  consequently,  such  part  of  the  volume  at  any  other 
temperature,  as  is  indicated  by  adding  the  number  of  de- 
grees above  32°  to  480. 

879.  The  rule  for  correction  to  be  applied  to  an  observed 
volume  of  gas  is,  therefore,  to  add  to  480  the  number  of  de- 
grees above  32°;  to  divide  the  observed  volume  by  this  sum, 
which   gives  the  expansion  or  contraction  for  each  degree  at 
the  observed  temperature;  to  multiply  this  by  the   number  of 
degrees  between  the  observed  temperature  and  the  tempera- 
ture to  which  the  gas  is  to  be  corrected,  which  will  of  course 
indicate   the   whole   expansion   or   contraction;    and  then 
to  subtract  this,  if  the  observed  be  above  the  corrected  tem- 
perature, or  to  add  it,  if  the  former  be  below  the  latter;  thus 
allowing   for  the  contraction   or   expansion   which    would 
actually  take  place,  if  the  temperature  of  the  gas  were  really 
to  be  brought  to  the  point  to  which  by  calculation   it  may 
thus  be  corrected. 

880.  As  an  illustration,  suppose  100  cubic   inches  of  gas 
at  70°  Fahrenheit  are  to  be  corrected  to  mean  temperature, 
or  60°.     The  difference  between   70°,  the  observed  tern-  * 
perature,  and  32°,  is  38,  which  added  to  480=  518;  the  100 
inches  divided  by  518,  gives  0.19305  of  a  cubic  inch  as  the 
whole   expansion   for   each   degree;   and    this     multiplied 
by  10,  the  difference  between  70°  and  00°,  gives  1.9305  cubic 


400  CORRECTION  FOR  PRESSURE. 

inches,  as  the  whole  expansion;  which,  subtracted  from  100 
cubic  inches,  leaves  98.0695  cubic  inches  as  the  volume 
which  would  be  occupied  by  the  gas  at  60°  Fahrenheit. 

881.  Or,  again,  suppose  the  100  cubic  inches  were  observed 
at  50°  instead  of  70°,  then  the  expansion  per  degree  is  ob- 
tained by  adding  18,  or  the  difference  of  32°  and  50°  to  480: 
this  equals  498,  and  dividing  100  cubic  inches  by  this,  we 
obtain  0.2008032  of  acubic  inch  as  the  expansion  per  degree 
at  50°;  and  this  multiplied  by  10,  the  difference  between  50° 
and  60°=2.008032  cubic  inches,  which  would  be  the  whole 
expansion  for  the  10°  from  50°  to  60°.     Being  added  to  100, 
it  makes  102.008032  cubic  inches  as  the  corrected  volume 
of  gas.  The  decimals  have  in  these  instances  been  calculated 
much  farther  than  will  be  necessary  except  in  particular  ex- 
periments, merely  with  a  view  of  showing  the  difference  in 
the  amount  of  the  corrections  required  for  an  equal  number 
of  degrees  at  different  temperatures. 

Correction  for  Pressure. 

882.  Boyle  and  Hooke  were  perhaps  the  first  to  observe 
that  the  volumes  of  gases  varied  inversely  in  proportion  to 
the  pressure  exerted  upon  them,  although  the  law,  having 
been  first  distinctly  announced  and  enlarged  upon  by  Mar- 
riotte,  has  received  his  name.     Its  truth  at  high  pressure, 
although  sometimes  doubted,  has  been  confirmed  by  the  re- 
sults of  Oersted*,  and  still  more  recently  by  those  of  MM.Du- 
long  and  Aragof ,  and  no  one  has  any  doubt  of  its  being 
accurately  true  at  such  pressures  as  occur  naturally  and  are 
indicated  by  the  barometer,  and  also  at  the  greater  variations 
dependant  upon  the  difference  of  level  of  the  fluid  with- 
in and  without  a  jar  standing  over  the  mercurial  or  water- 
trough  (767,  782). 

883.  A  pressure  of  30  inches  of  mercury,  as  observed  by 
an  accurate  barometer,  has  been  assumed  as  the  mean  height 
or  barometric  pressure,  and  volumes  of  gas  observed  at  any 
other  pressure  (780),  frequently  require  to  be  corrected  to 
what  they  would  be  at  this  point.     For  this  purpose  it  is  only 

*  Phil.  Mag.  Ixviii.  102.  t  Bib.  Universelle,  xlii.  p.338. 


CORRECTION  FOR  PRESSURE.  401 

necessary  to  compare  the  observed  height  with  the  mean 
height,  or  30  inches,  and  increase  or  diminish  the  observed 
volume  inversely  in  the  same  proportion.  Thus,  as  the  mean 
height  of  the  barometer  is  to  the  observed  height,  so  is  the 
observed  volume  to  the  volume  required.  As  an  instance, 
suppose  that  100  cubic  inches  of  gas  have  been  observed 
when  the  barometer  stood  at  30.7  inches :  then,  as  30  inches, 
or  mean  height,  is  to  30.7  inches,  or  observed  height,  so  is 
100,  or  the  observed  volume,  to  a  fourth  proportional  ob- 
tained by  multiplying  the  second  and  third  terms  together 
and  dividing  by  the  first:  thus,  30.7x100=3070,  which 
divided  by  30=162.333  cubic  inches  ;  this  would  be  the  vol- 
ume of  the  gas  at  30  inches  of  barometric  pressure.  Or, 
consider  the  gas  as  observed  at  28.9  inches  of  the  barometer: 
then  30  inches,  or  mean  height,  is  to  28.9  inches,  or  observed 
height,  as  100  is  to  96.333  cubic  inches,  that  being  the  result 
of  28.9  multiplied  by  100  and  divided  by  30,  according  to 
the  rule.  Again,  suppose  a  quantity  of  gas  amounting  to 
20  cubic  inches  standing  over  mercury  in  a  jar,  the  level 
of  the  metal  within  being  3  inches  above  that  without,  and 
the  barometer  at  29.4  inches  (800).  Then  the  column  of  3 
inches  of  mercury  within  the  jar,  counterbalancing  3  inches 
of  the  barometric  pressure,  instead  of  being  29.4  the  latter 
is  effectively  only  26.4,  and  the  correction  will  be  as  30 
inches  is  to  26.4  inches,  so  is  the  20  cubic  inches  observed 
to  17.6  cubic  inches,  the  volume  which  the  gas  would  really 
occupy  if  the  mercury  were  level  within  and  without  the  jar, 
and  the  barometer  were  at  30  inches. 


884.  It  is  constantly  necessary  to  make  corrections  both 
for  temperature  and  pressure  in  the  same  volume  of  gas.  It 
matters  not  which  correction  is  made  first,  the  result  being 
the  same  in  either  mode.  Thus  for  instance ;  1 00  cubic  inches 
observed  at  the  temperature  of  40°  Fahr.  the  barometer  be- 
ing at  28  inches,  if  first  corrected  for  pressure,  become 
93.33  cubical  inches  :  and  then  for  temperature  become 
97.158469,  which  is  the  true  volume.  Or,  if  first  corrected  for 
temperature,  it  becomes  104.02836,  and  then  for  pressure, 
it  becomes  as  before  97.158469  cubic  inches. 
3  A 


402  HALL'S  AEROMETER. 

885.  Dr  Mv  Hall  has  constructed  an  instrument*  which  he 
has  called  an  Aerometer,  intended  to  give  at  once  a  correc- 
tion for  changes  in  the  temperature  of  the  atmosphere  ;  in 
the  barometrical  pressure ;  in  the  external  and  internal 
heights  of  the  fluid  in  the  pneumatic  trough  ;  and  when  this 
trough  contains  water,  for  the  elevation  and  precipitation  of 
aqueous  vapour.  It  consists  of  a  bulb  of  glass  41  cubic 
inches  in  capacity,  attached  to  a  long  tube  whose  capacity 
is  1  cubic  inch.  This  tube  is  inserted  into  another 
tube  of  nearly  equal  length,  and  supported  on  a  stand, 
as  in  the  figure.  The  first  tube  may  be  sustained 
at  any  height  within  the  second  b^rneansof  a  spring 
at  the  upper  part.  Five  cubic  inches  of  air  at 
mean  temperature  and  pressure  are  introduced  in- 
to the  bulb  and  tube,  of  the  latter  of  which  it 
will  occupy  one  half;  the  other  half,  and  part  of  the 
tube  into  which  it  is  inserted,  are  to  be  occupied 
by  the  fluid  of  the  pneumatic  trough,  either  water  or 
mercury.  The  point  of  the  tube  at  which  the  air  and  fluid 
meet,  is  to  be  marked  5,  and  the  upper  and  lower  half  divided 
into  5  equal  parts,  indicating  tenths  of  a  cubic  inch  each. 
The  external  tube  is  to  be  marked  by  a  scale  of  inches. 

886.  When  the  volume  of  a  gas  confined  over  the  pneu- 
matic trough  in  jars  is  to  be  corrected  .by  the  indications  of 
this  instrument,  the  difference  between  the  levels  of  the  fluid 
in  the  jar  and  in  the  trough  is  to  be  measured,  and  the  same 
difference  occasioned  in  the  external  and  internal  heights  of 
the  fluid  in  the  aerometer.  The  gas  in  the  instrument,  and 
that  in  the  jar,  are  then  precisely  in  the  same  condition,  and 
by  observing  the  volume  of  the  former,  the  latter  may  be 
corrected.  Thus  if  it  be  5.2  cubic  inches  in  the,  aerometer, 
and  74  cubic  inches  in  the  jar,  then  as  5.2  is  to  5,  the  vol- 
ume in  the  instrument  at  mean  temperature  and  pressure,  so 
is  74  to  71.15,  the  corrected  volume  of  gas  in  the  jar. 

*  Quarterly  Journal  of  Science,  v.  52. 


403 


§  8.  Weighing  of  Gases  or  Jlir. 

887.  The  process  of  weighing  a  gas,  which  of  all  others  is 
simplest  in  principle,  is,  to  exhaust  a  light  globe  or  flask, 
fitted  with  a  cap  and  stop-cock  for  the  purpose,  then  exactly 
to  counterpoise  it  (64.65)  to  attach  it  to  a  graduated  transfer 
jar  containing  the  gas  to  be  weighed  (755),  and  after  allow- 
ing as  much  as  will  enter  to  pass  in,  permitting  the  tempera- 
ture to  become  that  of  the  atmosphere  (870),  and  equalizing 
the  pressure  within  and  without  the  jar,  to  estimate  the  vol- 
ume that  has  entered,  by  the  graduation.  Then  on  weighing 
the  vessel,  it  may  be  ascertained  how  much  it  has  increased 
in  weight,  and  the  increase  will  of  course  be  the  weight  of 
the  observed  volume  of  gas. 

888.  Globes  or  flasks  of  the  kind  required  are  sold  by  the 
instrument-maker.     They  should  be  perfectly  clean  and  dry 
when  used,  nothing  being  allowed  to  adhere  to  the  outside 
that  may  alter  their  weight  during  the  process.     The  tem- 
perature should  be  noted,  and  its  equality  carefully  preserved 
during  the  experiment ;  for  this  reason,  the  globe  should  be 
handled  with  all  the  delicacy  possible  (773).     The  pressure 
of  the  barometer  is  likewise  to  be  noted.     If  the  gas  be  in 
a  jar  standing  over  water,  it  must  be  let  in  carefully  (871}, 
the  little  piece  of  paper  before  recommended  being  intro- 
duced into  the  connecter  ;  and  it  is  advisable  to  let  a  small 
quantity  of  gas  pass  out  there,  before  the  parts  are  closely 
screwed  together,  that  the    common  air  in   them  may  be 
removed. 

889.  Gas,  when  standing  over  water,  becomes  saturated 
with  aqueous  vapour,  the  quantity  being  proportional  to  the 
temperature.      In   these  cases,  a  part   of  the  volume  ob- 
served, and  also  a  part  of  the  weight,  are  due  to  the  va- 
pour,   which    therefore    must   be  ascertained  before    the 
true  weight  of  the  gas  under  examination  can  be  determined. 
The  following  table  exhibits  the  proportion  by  volume  of 
aqueous  vapour  existing  in  any  gas  standing  over  or  in  con- 
tact with  water  at  the  corresponding  temperatures,  and  at 
mean  barometric  pressure  of  30  inches. 


404 


WEIGHING  OF  GAS  OR  AIR. 


40°  — 

.00933 

51°  — 

.01380 

61°  — 

.01923 

71°  — 

.02658 

41  — 

.00973 

52  — 

.01426 

62  — 

.01980 

72  — 

.02740 

42  — 

.01013 

53  — 

.01480 

63  — 

.02050 

73  — 

.02830 

43  — 

.01053 

54  — 

.01533 

64  — 

.02120 

74  — 

.02923 

44  — 

.01093 

55  — 

.01586 

65  — 

.02190 

75  — 

.03020 

45  — 

.01133 

56  — 

.01640 

66  — 

.02260 

76  — 

.03120 

46  — 

.01173 

57  — 

.01693 

67  — 

.02330 

77  — 

.03220 

47  — 

.01213 

58  — 

.01753 

68  — 

.02406 

78  — 

.03323 

48  — 

.01253 

59  — 

.01810 

69  — 

.02483 

79  — 

.03423 

49  — 

.01293 

60  — 

.01866    70  — 

.02566    80  — 

.03533 

50  — 

.01333 

890.  By  reference  to  this  table,  which  is  founded  upon 
the  experiments  of  Mr  Dalton  and  Dr  Ure,  and  includes  any 
temperature  at  which  gases  are  likely  to  be  weighed,  the 
proportions  in  bulk  of  vapour  present,  and  consequently  of 
the  dry  gas,  may  easily  be   ascertained.  *For  this  purpose 
the  observed  temperature  of  the  gas  should  be  looked  for, 
and  opposite    to  it  will  be  found  the    proportion  in  bulk 
of  aqueous  vapour  at  a  pressure  of  30  inches.     The  volume 
to  which  this  amounts  should   be  ascertained  and  corrected 
to  mean  temperature.     Then   the  whole  volume  is  to  be 
corrected  to  mean  temperature  and  pressure  (876),  and  the 
corrected  volume  of  vapour  subtracted  from  it.     This  will 
leave  the  corrected  volume  of  dry  gas.     It  has  been  ascer- 
tained in  a  manner  approaching  to  perfect  accuracy;  that  a 
cubic  inch  of  permanent  aqueous  vapour  corrected  to  the 
temperature  of  66°,  and  a  mean   pressure  of  thirty  inches, 
weighs  0. 1929  grains.     The  weight  therefore  of  the  known 
volume  of  aqueous  vapour  is  now  easily  ascertained,  and 
this  being  subtracted  from  the  weight  of  the  moist  gas,  will 
give  the  weight  of  the  dry  gas,  the  volume  of  which  is  also 
known. 

891.  As  an  illustration,  suppose  a  gas  standing  over  water 
had  been  thus  weighed,  and  that  220  cubic  inches  at  the 
temperature  of  50°  Fahr.,  and  barometric  pressure  of  29.4 
inches  had  entered  into  the  globe  and  caused  an  increase  in 
weight  of  101.  69  grains.  By  reference  to  the  table  it  will 
be  found  that  at  the  temperature  of  50°,  the  proportion  of 
aqueous  vapour  in  gas  standing  over  water  is  .01333,  which 
in  the  220  cubic  inches  will  amount  to  2.  933  cubic  inches, 
which  corrected  to  the  temperature  of  60°,  becomes  2.  942 
cubic  inches.  The  whole  volume  corrected  to  mean  tem- 
perature and  pressure  (878, 883)  will  be  found  to  equal 


WEIGHING    OF    GAS DESICCATION.  405 

219.929  cubic  inches,  from  which,  if  the  2.942  cubic  inches 
of  aqueous  vapour  present  be  subtracted,  it  will  leave 
216.987  cubic  inches  as  the  volume  of  dry  gas  at  mean 
temperature  and  pressure  :  2.942  cubic  inches  of  aqueous 
vapour  weigh  .5075  grains,  for  2.942X0.1929=0.5675; 
this  subtracted  from  101.69,  the  whole  weight,  leaves 
101.1225  grains,  which  is  the  weight  of  the  216.987  cubic 
inches  of  dry  gas;  and  by  the  simple  rule  of  proportion, 
therefore,  it  will  be  found  that  100  cubic  inches  of  such  gas, 
when  dried  and  at  mean  temperature  and  pressure  will 
weigh  46.603  grains. 

892.  It  is  not  necessary  in  this  experiment  that  the  globe 
or  flask  be  perfectly  exhausted  of  air  before  the  gas  be  ad- 
mitted, all  that  is  necessary  in   that  respect  being,  that  the 
quantity  of  gas  which  enters,  and  the  corresponding  increase 
of  weight,  be  known.    For  the  same  reason  it  is  not  necessary 
that  the  globe   be  filled,  provided  the   quantity  which  does 
enter  is  ascertained  upon  the  graduation  of  the  jar  when  the 
level  is  the  same  inside  and  outside ;  and  that  no  alteration 
of  the  quantity  in  the  globe  be  allowed  before  the  weighing 
is  completed.     The  state  and  quantity  of  the  gas  is  estima- 
ted in  the  Jar,  and  it  is  there  that  the  temperature  and  pres- 
sure should  be  attended  to.     It  is  essentially  necessary  that 
the  temperature  of  the  gus  over  the  water  should  have  been 
steady  for  some  time  before  the  experiment  be  made,  and 
that  it  do  not  change  until  the  gas  has  entered  the  globe  and 
the  stop-cock  is  securely  closed.     After  that,  a  little  varia- 
tion of  temperature  is  of  no  consequence,  so  that  nothing 
passes  into  or  out  of  the  globe  until  the  conclusion  of  the 
experiment.     The  globe,  as  before   said  (888),  should  be 
clean  and  dry. 

893.  Some  experimenters  prefer  drying  the  gas  before  it  is 
weighed,  and  thus  in  fact  weigh  a  known  volume,  not  of  a 
mixture,  but  of  pure  gas.    Now  gases  are  dried  in  various 
ways.    One  method  is  to  pass  them  through  a  glass  tube,  con- 
taining substances  having  powerful  attractions  for  water.  It  is 
a  simple  and  a  useful  process,  and  therefore  proper  to  be  de- 
scribed here,  though  not  conveniently  applicable  to  the  mode 
of  weighing  a  gas  as  above  directed,  because  of  the  greater 
difficulty  of  measuring  the  quantity  of  gas  which  enters. 


406  DESICCATION SUBSTANCES  USED. 

The  tube  may  be  about  half  an  inch  in  diameter,  and  from  12 
to  20  inches  long;  it  should  have  a  piece  of  wire  pressed  into 
a  loose  ball,  thrust  into  one  end  of  it,  to  prevent  fragments 
falling  through.  Chloride  of  lime*  should  be  heated  and 
fused  in  an  earthenware  crucible,  a  temperature  below  that 
of  visible  redness  being  quite  sufficient  for  the  purpose,  then 
poured  upon  a  clean  metallic  or  stone  surface,  and,  as  soon 
as  it  has  solidified,  broken  up  and  put  into  stopped  bottles. 
This  chloride  being  divided  into  a  mixture  of  large  and  small 
fragments  is  to  be  introduced  rapidly  into  the  tube,  until  the 
latter  is  nearly  full;  the  apparatus  is  then  ready  for  use.  The 
tube  may  be  connected  with  the  jar,  gasometer,  or  other 
vessel,  containing  or  evolving  the  gas,  by  caoutchouc  con- 
necters (449),  or  in  any  other  convenient  way;  and  so  much 
gas  should  be  passed  through  it  as  effectually  to  expel  all  the 
common  air  before  the  gldbe  or  vessel  to  be  filled  with  the  dry 
gas  be  attached.  That  being  done,  the  gas  should  be  allowed 
to  pass  slowly,  100  cubical  inches  having  from  10  to  20 
minutes  allowed  for  their  passage  through  such  a  tube  as  that 
described,  though  if  the  period  be  lengthened,  no  injury  is 
occasioned.  If  the  jtube  be  shorter,  or  of  smaller  diameter, 
more  time  should  be  proportionately  allowed. 

894.  Instead  of  chloride  of  lime,  fused  potash,  or  fused 
carbonate  of  potash  may  be  employed;  but  it  is  to  be  remem- 
bered that  ordinary  potassa  fusa  generally  evolves  a  little 
oxygen  during  its  solution,  and  hence  may  occasionally  be 
exceptionable.  Chloride  of  lime  will  not  answer  for  ammonia, 
or  for  sulphurous  and  some  other  acid  gases.  Potash,  or 
carbonate  of  potash,  answers  perfectly  well  for  ammonia,  but 
not  for  acid  gases.  Sulphuric  acid  is  a  very  excellent  desic- 
cator for  many  gases,  and  may  be  used  in  a  tube  by  first 
curving  the  tube,  then  filling  it  with  fragments  of  glass  or  rock 
crystal,  and  afterwards  pouring  in  so  much  concentrate  oil 
of  vitriol  as  shall  moisten  the  fragments,  but  not  cause  ob- 
struction to  the  passage  of  the  gas.  By  moving  the  tube  a 
little  from  time  to  time,  the  acid  is  made  to  pass  from  place  to 
place,  it  becomes  mixed,  and  it  remoistens  the  fragments, 
which  from  the  previous  quiescent  state  of  the  apparatus  may 

*  Chloride  of  calcium,  or  muriate  of  lime,  heated  to  redness,  is  usually  resort- 
ed to.     Chloride  of  calcium  is  also  formed  by  heating  the  chloride  of  lime. — ED. 


DESICCATION  OF   GASES — TUBES.  407 

have  drained  considerably.     This  substance  is  effectual  with 
almost  all  gases  except  ammonia. 

895.  In  any  case  where  tubes  like  these  are  to  be  used  for 
drying  the  gas  to  be  weighed  in  the  manner  already  described, 
and  consequently  requiring  to  be  measured,  the  gas  must  be 
delivered  from  a  graduated  jar,  and  after  the  quantity  which 
is  to  expel  the  atmospheric  air  has  passed  through,  and  the 
exhausted  vessel  is  attached  to  the  end  of  the  drying  tube,  the 
level  within  and  without  the  jar  should  be  equalized  and  the 
quantity  of  gas  noted;  and  again  also,  when  so  much  gas  has 
passed  from  the  jar  as  has  sufficed  to  fill  the  globe,  and  when 
its  temperature  is  the  same  as  that  of  the  surrounding  air. 
It  will,  however,  be  evident  that  in  these  cases  the  quantity 
that  has  entered  the  globe  is  not  equal  to  that  which  has  left 
the  jar,  for  a  certain  volume  of  vapour  has  been  abstracted. 
This  must  be  ascertained  by  noticing  the  temperature  of  the 
moist  gas,  and  correcting  its  volume  to  the  pressure  of  30 
inches  of  mercury;  then  ascertaining  by  the  table  (889)  the 
proportion  of  vapour  which  was  present  in  the  volume  which 
left  the  jar,  and  which  is  to  be  subtracted  from  the  corrected 
volume,  and  the  remainder  will  be  the  volume  of  dry  gas 
which  has  entered  the  globe. 

896.  Desiccating  tubes,  similar  to  those  which  have  been 
described,  are  very  convenient  for  drying  gas  in  numerous 
cases,  without  reference  to  the  operations  of  weighing,  and 
where  no  account  of  volume  is  kept.     They  may  be  of  various 
sizes,  some  indeed  not  more  than  five  or  six  inches  in  length, 
and  the  fourth  or  fifth  of  an  inch  in  diameter.     The  tube 
should  be  drawn  out  at  one  end  to  a  conical  form,  with  a 
capillary  opening;  the  desiccating  substance  should  be  intro- 
duced, and  the  other  end  drawn  out  in  a  similar  manner  to  the 
former.  The  capillary  apertures  are  easily  sealed  hermetically 
by  holding  them  for  a  moment  in  a  flame,  and  the  tubes  may 
be  preserved  in  that  state  until  wanted.     When  required,  the 
ends  should  be  broken  off,  so  as  to  open  small  apertures,  and 
the  tube  should  be  attached  to  the  gas  apparatus  by  caout- 
chouc  connecters  (449);  or  in  any  other  manner,  so  as  to  permit 
the  gas  to  pass  through  it.     When  the  operation  is  finished, 
and  the  tube  dismounted,  the  gas  within  may  be  blown  out 


408          GASES  DRIED  OVER  MERCURY SULPHURIC  ACID. 

by  bellows,  or  drawn  out  by  the  mouth,  the  ends  of  the  tube 
be  sealed  as  before,  and  the  tube  itself  reserved  for  use  an- 
other time.  It  will  in  this  way  be  repeatedly  serviceable,  until 
so  much  water  has  been  abstracted  by  it  as  to  injure  its  desic- 
cating power.  The  drying  effect  of  these  tubes  is  in  all  cases 
increased  by  lowering  their  temperature,  which  may  very 
conveniently  be  done  when  the  tube  is  bent,  as  has  been  men- 
tioned with  respect  to  sulphuric  acid  (894),  by  dipping  the 
bent  part  into  a  mixture  of  ice  and  salt  (454). 

897.  In  other  cases,  gas  confined  over  mercury,  either  at 
the  trough  or  in  a  gasometer,  may  be  dried  by  desiccating  sub- 
stances, as  chloride  of  lime,  previously  placed  within  the  jar: 
or  gas  dried  by  being  passed  through  the  desiccating  tubes 
(893),  may  be  conveyed  into  a  graduated  jar  over  mercury, 
thence  transferred  into  the  exhausted  globe  and  may  actually 
be  measured  in  its  dry  state. 

898.  A  sulphuric  acid  bath,  or  gasometer,  may  be  used 
with  great  advantage  in  the  desiccation  of  particular  gases,  as 
chlorine,  or  in  very  important  experiments.     For  this  pur- 
pose a  graduated  transfer  jar  should  be  selected,  and  a  com- 
mon glass  jar  for  the  retention  of  fluids;  the  latter  of  a  size 

just  sufficient  to  receive  the  former,  and  allow  it 
free  motion.  The  latter  jar  is  to  be  filled  with  sul- 
phuric acid  except  about  an  inch  of  the  top,  when 
if  the  transfer  jar  be  depressed  in  it,  whilst  the  air 
escapes  above  (755),  it  will  become  filled  with  the 
acid.  The  gas  to  be  dried  is  then  to  be  introduc- 
ed by  the  stop-cock,  the  connexion  of  the  appara- 
tus being  made  by  caoutchouc  tubes,  or  otherwise, 
as  may  be  convenient.  As  the  sulphuric  acid  must  not  rise 
into  the  cap  or  stop-cock,  and  as  air  will  consequently 
occupy  those  places,  it  is  needful,  after  the  gas  has  passed 
in  to  the  depth  of  an  inch  or  a  little  more,  to  detach  the  jar 
and  throw  out  that  portion,  by  which  means  very  little  of  the 
common  air  will  remain.  The  apparatus  is  now  to  be  re- 
attached,  the  gas  introduced  as  before,  and  allowed  to  accu- 
mulate in  the  jar.  When  the  jar  is  nearly  full,  the  stop-cock 
is  to  be  closed,  and  the  gas  left  over  the  sulphuric  acid  for  an 
hour  or  two.  During  this  time  the  jar  may  rest  on  the 


WEIGHING  OF  GASES THOMSON'S  METHOD.  409 

sulphuric  acid;  or  if  there  be  any  danger  of  an  overflow,  the 
jar  may  be  blocked  up  by  a  cork  put  between  it  and  the 
outer  jar,  or  it  may  be  supported  in  part  by  a  string  tied  to 
the  stop-cock  and^made  fast  to  a  nail  or  some  other  projec- 
tion. When  the  gas  is  dried,  it  is  to  be  used  in  any  way 
that  may  be  desired,  being  transferred  through  the  stop-cock 
and  its  quantity  measured  upon  the  graduation,  after  the  level 
of  the  sulphuric  acid  within  and  without  the  jar  has  been 
equalized. 

The  original  mercurial  gasometer  of  Mr  Clayfield,  without 
tubes  (809),  is  an  excellent  instrument  for  the  desiccation  of 
gas  over  sulphuric  acid,  being  altogether  of  glass. 

899.  The  desiccators  mentioned,  namely,  chloride  of  cal- 
cium, potash,  carbonate  of  potash,  and  sulphuric  acid,  are 
adapted  for  all  gases,  one  being  applicable  when  another  is 
not.     Sometimes  dry  lime  in  tubes  is  used  in  slow  processes, 
but  has  no  advantage  over  those   bodies,  except  that  it  is 
more  economical  in  large  experiments. 

900.  Returning  to  the  methods  of  weighing   gases:  Dr 
Thomson    has    published  one*    which,    being   exceedingly 
simple  in  principle,  relates  to  the  determination  of  their  re- 
lative specific  gravities,  and  requires  description.     The  globe 
or   flask    (888),    with  its  stop-cock,    is   to  be   weighed  as 
accurately  as  possible,  then  exhausted  and  weighed  again. 
The   loss  of  weight  sustained  is  equal   to   the  quantity  of 
common    air   drawn   out,    and  is  less  or    more  according 
to  the  size  of  the  flask   and  the  goodness  of  the  exhaus- 
tion.   The    flask  is  then  to  be  filled  with  the  gas  whose 
specific  gravity  is  wanted  (869).     All  the  precaution  neces- 
sary, according  to  Dr  Thomson,  is,  to  take  care  that  no  par- 
ticles of  water  or  mercury  (supposing  the  gas  to  be  standing 
over  mercury)  insinuate  themselves  into  the  flasks.     It  is  ob- 
vious that  the  volume  of  gas  which  will  enter  the  flask  will 
be  precisely  equal  to  the  volume  of  common  air  that  has 
been  previously  drawn  out  of  it  by   the  air-pump.     The 
flask  thus  filled  with  the  gas,  whose  specific  gravity  is  tp  be 
known,  is  now  to  be  weighed,   and   the   increase  aboue  its 

*  Annals  of  Philosophy,  xv.  232. 

3  B 


410  WEIGHING  OF  GASES PRECAUTIONS. 

weight  when  exhausted,  gives  exactly  the  weight  of  the  gas 
introduced.  This  weight  divided  by  the  weight  of  the  com- 
mon air  removed  by  the  pump,  gives  the  specific  gravity  of 
the  gas,  that  of  air  being  assumed  as  un|te  or  1;  and  this  is 
done  without  any  measurement,  or  the  necessity  of  any  cor- 
rection for  temperature,  or  for  the  weight  of  the  barometer, 
which  remain  unchanged  during  the  short  time  of  the  ex- 
periment. 

901.  Notwithstanding  the  simplicity  of  the  principle,  how- 
ever, much  caution  and  even  correction  is  necessary,  without 
which  it  would  be  unsafe  to  recommend  the  process  to  the 
student.     It  is  especially  requisite  that  no  gas  of  a  preceding 
experiment  remain  in  the  globe;  for  which  reason,  after  one 
experiment  is  finished,  or  before  another  has  commenced,  the 
globe  or  flask  should  be  exhausted  many  times,  air  being 
admitted  after  each  time;  or  if  access  to  the  interior  be  easy, 
much  air  should  be  drawn  or  blown  through  it. 

902.  The  air  which  is  in  the  globe  is  the  same  as  that  of 
the  atmosphere  at  the  time  it  was  introduced,  and  is  there- 
fore liable  to  all  the  variations  to  which  the  atmosphere  it- 
self is  subject.     Now  the  weight  of  a  given  bulk  of  the  at- 
mosphere at  the  same  temperature  and  pressure,  varies  at 
different  times,  because  of  the  variable  proportions  of  water 
and  perhaps  other  substances  which  it  contains.     It  is  not 
often  saturated  with  moisture,  and  is  never  quite  dry,  and 
would  require  bothhygrometrical  experiment  and  calculation 
for  a  knowledge  of  its  true  state  at  any  particular  period. 
By  reference  to  Daniell's  tables  of  observation,  it  will  be 
found  that  a  difference  in  the  dryness  of  the  air,  amounting 
to  20  degrees  of  the  hygrometer  when  the  air  was  at  the 
temperature  of  60  degrees,  has  been  observed  within  three 
days,  there  being  at  one  time  1.053  cubic  inches  of  vapour 
present  in  100  cubic  inches  of  the  air,  and  at  another  1.98 
cubic  inches :  a  difference  of  .927  cubic  inches  of  vapour 
(uncorrected  for  temperature)  having  occurred  in  that  short 
period. 

9^3.  If  the  air  in  the  globe  were  dried,  it  would  then  be 
almost  constantly  the  same  in  weight ;  for  its  two  important 
ingredients  vary  very  slightly,  if  at  all,  and  the  difference  in 


WEIGHING  OF  GASES— CORRECTIONS.  411 

their  weight  is  so  small  as  to  make  these  variations  of  no  con- 
sequence. The  carbonic  acid  in  the  air  is  in  very  small  quan- 
tity, and  though  variable  can  hardly  interfere,  except  under 
particular  circumstances.  It  may  on  very  important  occa- 
sions be  removed  by  alkali. 

904.  No  choice  can  be  permitted  in  this  process,  as  to 
passing  in  the  gas  in  a  dry  or  moist  state ;  it  must  of  necessity 
be  dry.     For  though,  if  admitted  when  saturated,  the  pro- 
portion of  the  vapour  may  be  deduced  from  the  temperature 
by  reference  to  the  table  (889),  and  its  specific  gravity  may 
be  considered  as  known,  yet  as  the  whole  volume  of  gas  in- 
troduced is  unknown,  and  the  specific  gravity  is  as  yet  un- 
known, there  is  no  way  of  ascertaining  the  actual  weight  or 
volume  of  the  vapour  present,  without  which  the  correction 
for  moisture  cannot  be  applied;  it  is,  therefore,  necessary  that 
the  gas  should  be  dried  (893)  by  some  one  of  the  processes 
already  described,  and  then,  if  the  air  in  the  globe  be  dried 
also,  without  knowing  the  volumes  and  without  correction 
for  barometer  or  thermometer  (provided  they  do  not  change 
during  the  experiment),  the  relative  specific  gravities  of  air 
and  the  gas  maybe  ascertained,  and  by  similar  experiments, 
of  air  and  any  other  gas.     Thus,  suppose  the  globe  by  ex- 
haustion lost   45.28  grains,  and   by  admitting  dry  oxygen 
gas  gained  50.7  grains,  50.7  -r-45.28  =  1.1197,  the  specific 
gravity  of  that  oxygen  gas,  common  air  being  1.      Then 
clearing  out  the  globe,  and  replacing  its  contents  by  pure 
dry  air  (901),  suppose  the  experiment  repeated  with  dry 
sulphurous  acid  gas,  the  globe  losing  this  time  only  40.25 
grains,  and  gaining  by  the  entrance  of  the  sulphurous  acid 
90.37  grains,  then  99.37  -*-  40.25  =  2.245,  the  specific  grav- 
ity of  sulphurous  acid,  air  being  1. 

905.  But  if  the  volume  of  the  gas  admitted  be  measured 
(887),  it  may  then  be  saturated  with  moisture  ;  but  now  the 
temperature  and  pressure  must  be  known.     The  temperature 
being  known,  the  volume  of  the  aqueous  vapour  admitted 
with  the  gas  may  be  ascertained  by  reference  to  the  table 
(889,891) ;  and  then,  being  corrected  for  temperature,  its 
weight  also  may  be  ascertained ;  and  by  subtraction  of  it 
from  the  whole  weight  gained,  the  weight  of  the  dry  gas  ad- 


412  SATURATING  GASES  WITH  MOISTURE. 

milted  is  known.  Now  diminishing  the  weight  of  the  com- 
mon air  taken  out  by  a  proportion  equal  to  the  volume  of 
the  vapour  in  the  gas,  the  rest  is  the  corresponding  weight 
of  air  of  a  bulk  equal  to  that  of  the  dry  gas,  and  dividing  the 
latter  by  the  former,  the  specific  gravities  are  ascertained. 
The  proportion  in  bulk  between  the  gas  and  the  vapour 
mixed  with  it,  required  in  the  latter  part  of  this  calculation, 
is  to  be  obtained  by  correcting  the  whole  volume  of  gas 
to  the  pressure  of  30  inches,  and  then  subtracting  the  vol- 
ume of  vapour  from  it. 

906.  On  the  whole,  it  is  better  perhaps  in  this  method  that 
both  the  air  and  the  gas  should  be  saturated  with  aqueous 
vapour,  the  temperature  being  known,  and  the  same  for  both. 
This  is   easily  done   by  exhausting  the  globe  or   flask,  and 
filling  it  with  common  air   from  a   receiver  over  the   same 
water  as  the  gas  ;  then  counterpoising  it,  exhausting  it  more 
or  less,  ascertaining  the  loss  of  weight,  supplying  the  place 
of  the  air  taken  out  by  the  gas,  observing  the  quantity  ad- 
mitted and  weighing  it  again.     Thus  the  equal  volumes  of 
moist  air  and  gas,  their  weights  and  temperature,  become 
known  ;  from  the  quantity  and  temperature  of  either,  the  vol- 
ume of  aqueous  vapour  at  the  pressure  of  30  inches  may  be 
deduced  by  the  table  (889),  and  is  the  same  for  both.    The 
weight  of  this,   when  reduced    to  mean  temperature,  may 
easily  be  ascertained,  and  that  being  equally  subtracted  from 
the  observed  weights  of  the  common  air  and  the  gas,  leaves 
the  actual  weights  of  equal  dry  volumes  of  air  and  of  the 
gas  ;  from  which  the  specific  gravity  is  easily  deduced  as  be- 
fore by  division. 

907.  As  an  illustration  of  this  method,  suppose  the  globe 
to  be  filled  with  air  from  over  water,  then  balanced,  after- 
wards exhausted,  and  the  loss  of  weight  found  to  be  34.6 
grains;  on  letting  in  the  moist  gas,  suppose  that  112  cubic 
inches  entered,  and  that  the  gain  of  weight  was  52  grains, 
the  temperature  being  52°  Fahrenheit,  and  the  barometer  at 
29.3  inches.     At  52°,  the  proportion  of  aqueous  vapour  in 
volume  is,  01426,  which  of  112  cubic  inches,  is  1.597  cubic 
inches  ;  this  quantity  corrected  to  mean  temperature  =1.623 
cubic  inches;  and  this  equals  0.313  grains  of  aqueous  va- 


WEIGHING  GASES TUBE-CHEMISTRY.  413 

pour;  the  subtraction  of  this  weight  equally  from  the  weights 
of  the  moist  air  and  gas,  leaves  34.287  grains  for  the  weight 
of  dry  air,  and  51.687  grains  for  the  weight  of  an  equal  vol- 
ume of  dry  gas.  In  this  way  any  slight  errors  in  measuring 
are  important,  but  care  is  requisite  as  to  the  constancy  of 
temperature. 

908.  In  all  experiments  upon  the  weight  of  gases,  it  will 
be  proper  to  leave  the  globe  full  of  pure  common  air ;  all  re- 
mains of  the  gases  which  have  been  in  use,  having  been  re- 
moved before  the  apparatus  is  put  away. 


SECTION  XVI. 
TUBE  CHEMISTRY. 

909.  FREQUENT  occasion  has  occurred  in  the  preceding 
parts  of  this  volume  for  a  reference  to  apparatus  formed 
partly  or  altogether  of  glass  tube.     The  object  of  this  sec- 
tion is  to  show  the  important  uses  of  apparatus  of  that  des- 
cription.    The  facility  with  which  it  supplies  the  absenct 
of  many  complicated  instruments;  the  consequent  economy 
and  readiness  of  chemical  practice;  and  the  peculiar  advan- 
tages of  it  when  rare  and  valuable  substances  are  under  ex- 
amination, are  the  inducements  to  collect  the  information 
upon  this  subject  into  one  focus. 

910.  The  material  required  for  the  construction  of  this 
kind  of  apparatus  is  glass  tube  of  half  an  inch  in  diameter, 
or  less,  and  of  different  degrees  of  thickness.      The  most 
useful  sort  is  quill  tube,  the  glass  being  of  the  thickness  of 
card  or  thin  pasteboard.     Three-square  or  edge  files  are  re- 
quired for  cutting  tho  tube  into  lengths.     If  the  table  blow- 
pipe and  lamp  (242)  be  not  at  hand,  most,  and  indeed  all 
the  apparatus  may  be  made  by  a  spirit-lamp  and  a  mouth 
blow-pipe  (216).     To  these  should  be  added  a  drawer  full 
of  tubes,  closed  at  one  end,  of  various  diameters,  and  all 
lengths   from  one  inch  to  five  or  six.      The  fragments  of 


414  TUBE-CHEMISTRY — PRECIPITATION. 

tubes,  which  are  continually  occurring,  should  be  worked 
up  into  these  forms  at  every  opportunity,  according  to  the 
direction  to  be  given,  (1165,  &c.)  and  are  then  ready  for 
use. 

911.  These  tubes  answer  all  rife  purposes  of  test-glasses, 
and  in  the  small  way  precipitates  are  made,  preserved,  and 
washed  very  conveniently  in  them.  They  are  easily  sup- 
ported in  a  tumbler  or  wine-glass,  or  they  may  be  supplied 
individually  with  stands,  by  inserting  them  in  perforated 
corks  (67).  Those  who  frequently  use  them  will  find  a  tube- 
rack  very  convenient.  It  may  be  formed  of  two  boards,  one 
supported  two  or  three  inches  above  the  other,  and  the 
upper  pierced  with  holes  to  admit  the  tubes.  Or  a  very 
simple  one  may  be  made  of  a  board  a  foot  in  length  and 
six  inches  in  wfclth,  having  a  piece  of  coarse  wire  trellis 
about  three  inches  above  it,  supported  at  the  corners  by 
upright  pieces  of  strong  wire.  The  apertures  in  the  trellis 
serve  to  receive  and  retain  the  tubes.  A  dropping-bottle 
(402)  is  necessary  in  experiments  with  these  tubes,  for  the 
supply  of  small  quantities  of  water,  or  for  washing  precipi- 
tates from  the  sides. 

912.  When  in  precipitating  or  testing  (504,  &c.)  agitation 
ts  required,  it  may  be  given   by  closing  the  tube  with  the 
finger,  and  shaking  the  contents  together  from  top  to  bottom. 
Or,  if  the  finger  be  likely  to  communicate  impurity,  and  so 
interfere  with  the  experiment,  or  be  itself  liable  to  injury, 
then  a  clean  glass  rod,  about  half  the  diameter  of  the  tube, 
if  raised  and  lowered  in  the  fluid,  will  readily  and  perfectly 
mix  it.     Occasionally,  with  corrosive  fluids,  the  tube  may  be 
held  rather  stiffly  at  top  in  one  hand,  and  the  fore-finger  of 
the  other  passed  rapidly  backward  and  forward  by  the  bot- 
tom, so  as  to  strike  it  each  time,  and  thus  give  rapid  agitation 
to  the  contents,  if  they  are  not  in  too  great  quantity.     Such 
ordinary  agitation  as  would  effectually  mix  fluids  in  a  glass 
or  bottle,  is  insufficient  for  the  same  purpose  in  these  narrow 
vessels,  especially  when  the  depth  of  fluid  is  more  than  an 
inch. 

913.  When   delicate  testing  operations  are  in  progress, 
tubes  are  exceedingly  convenient,  owing  to  the  facility  with 


WASHING  IN  TUBES HEATING.  4  I  5 

which  a  little  of  the  fluid  to  be  tested  may  be  compared  with 
the  portions  to  which  tests  have  been  added.  It  is  scarcely 
possible  that  the  slightest  change  can  pass  unnoticed  when 
the  two  are  examined  by  each  other. 

914.  The  washing  and  separation  of  small  quantities  of 
insoluble  fluids  and  fusible  solids,  is  well  effected  in  tubes. 
An  extemporary  instrument  for  the  former  purpose,  made  of 
tube,  has  been  already  described  (559).     In  consequence  of 
the  facility  with  which  heat  may  be  applied,  it  is  easy  to  melt 
a  fusible  body  in  a  tube  ;  thus  naphthaline  may  be  fused  with 
water  or  a  solution  of  potash,  and  if  mixed  well,  and  after- 
wards left  to   separate  and  cool,  it  will  be  obtained  in  a 
cleansed  state  and  a  very  convenient  form.     In  such  cases 
it  is  advantageous  to  let  two  pieces  of  wire  remain  in  the 
tube  until  all  is  cold:  one  is  to  pass  through  the  naphthaline 
into  the  water  beneath ;  the  other,  bent  at  the  lower  end,  is 
to  be  placed  in  the  naphthaline,  and  retained  there  by  turn- 
ing the  upper  part  of  it  over  the  edge  of  the  tube.     If  the 
straight  wire  be  first  pulled  out,  a  passage  for  air  is  opened, 
in  consequence  of  which  the  piece  of  naphthaline  may  itself 
be  drawn  out  with  facility  by  the  second  wire.     Wax,  cam- 
phor, and  other  equally  fusible  bodies  may  be  experimented 
with  in  the  same  manner. 

915.  As  already  observed,  these  tubes  will  bear  heat,  its 
application  being  easy  and  convenient  either  by  sand-baths, 
spirit-lamps  or  other  means.     Hence  they  supply  the  place 
of  flasks  (400)  as  well  as  glasses,  and  many  operations  (259) 
both  hot  and  cold,  as  those  of  solutions,  digestions,  &c., 
may  be   performed  in  them    with  numerous    advantages, 
amongst  which  is  the  important  one  of  easily  witnessing  what 
is  going  forward.     Solutions  in  acids  are  readily  effected 
(400,  &c.),  and  the  action  upon  a  substance,  or  the  changes 
in  the  appearance  of  the  solid  and  fluid  may  be  watched  at 
every  moment  in  the  most  advantageous  manner. 

916.  The  surface  of  a  body  which  has  been  partly  acted 
upon,  is  frequently  better  seen  in  a  tube  when  surrounded 
by  fluid,  than  it  can  be  even  in  the  air;  and  this  is  still  more 
particularly  the  case  with  such  bodies  as  change  in  the  air, 
or  that  cannot  be  washed  or  dried  without  injury.     For  this 


416  TUBES HANDLES BOILING  UNDER  PRESSURE. 

reason  the  crystallizations  which  are  formed  from  hot  solutions 
as  they  cool  in  tubes,  are  more  advantageously  examined  in 
that  way  than  in  any  other  (575) ;  and  as  the  cooling  can  be 
retarded  to  almost  any  degree,  either  by  wrapping  the  hot 
tube,  with  its  contents  in  flannel,  or  else  immersing  it  in  a 
large  quantity  of  hot  matter,  and  enveloping  the  whole,  this 
method  is  often  superior  to  any  other. 

917.  The  arrangement  of  tube-baths  for  the  conveyance  of 
limited  temperatures  either  by  the  intermedium  of  water,  so- 
lutions, or  metals,  has  already  been  described  with  sufficient 
explicitness  (259,263,  265). 

918.  Tubes  when  heated  sometimes  acquire  temperatures 
which  make  them  untenable  in   the  unguarded  hand ;  this 
inconvenience  is  easily  obviated  by  folding  a  piece  of  paper 
about  three  inches  square  three  or  four  times  in  one  direc- 
tion, so  as  to  form  a  band  of  eight  or  twelve  thicknesses, 
passing  this  round  the  tube  near  the   top,  and  twisting  the 
two  ends  together  into  a  handle.     The  conducting  power  of 
the  paper  is  so  small,  that  such  a  handle  prevents  the  passage 
of  any  heat  by  which  the  hand  might  suffer  inconvenience. 
A  very  convenient  handle  may  also  be  made  of  a  sound  cork 
perforated  so  as  to  form  a  ring,  which  is  to  be  cut  through 
with  a  knife  in  one  place.     Half  a  dozen  of  these  will  supply 
handles  to  most  tubes  ;  they   merely  require  to  be  slipped 
upon  them,  and  will  clasp  the  vessel  like  a  spring.     Occa- 
sionally, a  piece  of  square  or  angular  cork,  or  the  half  of  a 
rounded  cork,  or  one  that  does  not  fit  tightly,  being  inserted 
in  the  mouth  of  the  tube,  forms  a  useful  handle  (1174);  these 
are   more  particularly  required  in  sublimations,  where  the 
whole  of  the  surface  of  the  tube  is,  if  possible,  to  be  exposed 
to  view. 

919.  In  consequence  of  the  small  diameter,  and,  therefore, 
small  sectional  area  of  tubes,  they  are  much  stronger  re- 
latively to  internal  pressure  than  larger  vessels,  such  as 
flasks  of  the  same  thickness.     An  advantage  is  thus  gained  in 
some  cases  of  solution  or  digestion  in  certain  fluids,  as  alco- 
hol, ether,  and  even  water,  because  it  enables  the  experimen- 
ter to  subject  the  substances  to  temperatures  as  high  as  the 
boiling  points  without  loss  of  the  fluid  (400),  or  occasionally 


BOILING  UNDER  PRESSURE  IN  TUBES.  417 

to  temperatures  still  higher  (99),  the  ebullition  going  on  as 
it  were  under  pressure.  This  is  easily  performed  with  alco- 
hol, ether,  and  similarly  volatile  fluids,  in  tubes  of  four,  five, 
or  six  inches  in  length,  and  of  such  diameter  as  to  be  readily 
and  perfectly  closed  by  the  finger.  Suppose  a  tube  of 
this  kind,  one  third  filled  with  alcohol,  and  held  tightly  be- 
tween the  thumb  and  second  finger  of  the  left  hand,  its  ori- 
fice being  closed  by  the  fore-finger  of  the  same  hand.  The 
fore-finger  is  to  be  relaxed,  and  the  heat  of  a  spirit-lamp  ap- 
plied until  the  alcohol  begins  to  boil;  the  fore-finger  is  then 
to  be  re-applied  closely,  and  it  will  be  found  that  the  flame 
of  the  lamp,  applied  at  intervals,  is  quite  sufficient  to  keep 
the  temperature  up  to  the  boiling  point.  No  alcohol  can 
evaporate,  for  the  finger  has  power  sufficient  to  retain  the  va- 
pour even  were  its  force  equal  to  two  atmospheres,  and  the 
tube  itself  is  also  strong  enough  to  resist  the  same  force. 

920.  This  operation  is  very  advantageous  when  valuable 
and  volatile  solvents  are  in  use;  it  is  therefore  worth  while  to 
refer  to  those  points  which  indicate  the  state  and  temperature 
of  the  fluid,  and  which  make  the  practice  easy.  If  the  fluid 
be  one  which,  like  alcohol,  when  at  or  above  its  boiling  point, 
is  at  a  temperature  inconvenient  to  the  hand,  then,  if  all  the 
common  air  were  allowed  to  pass  out  of  the  tube  before 
closing  it,  the  whole  tube  would  become  heated  by  the  va- 
pour rising  from  the  hot  liquid  beneath,  and  the  fingers 
would  be  injured;  but  by  not  allowing  all  the  air  to  escape, 
that  portion  which  is  retained  in  the  tube  is  always  forced  to 
the  top  by  successive  formation  and  condensation  of  the  va- 
pour below,  and  interfering  with  the  passage  of  the  hot 
vapour  to  the  part  which  it  occupies,  it  preserves  that  por- 
tion of  the  tube  at  comparatively  low  and  very  bear- 
able temperatures.  The  part  thus  retained  at  a  low  tem- 
perature is  proportionate  to  the  quantity  of  air  confined  in  the 
tube;  this  quantity  is  usually  a  proper  one  if  the  tube  be 
closed  just  after  the  alcohol  has  begun  to  boil,  and  before 
the  upper  part  of  the  tube  has  been  heated.  If  too  much 
air  has  been  expelled,  and  the  tube  is  found  to  become  hot 
above,  the  application  of  the  flame  must  be  suspended  a 
moment  or  two,  the  whole  suffered  to  cool  below  the  boiling 
3  C 


418  THE  DEGREE  OF  PRESSURE DISTILLATION. 

point,  the  tube  opened,  the  upper  part  cooled  slightly  by  a 
piece  of  moist  paper  or  a  cold  finger,  and  then  the  fore-fin- 
ger is  to  be  re-applied  to  close  it  as  before. 

921.  The  state  of  the  fluid  within  is  in  part  indicated  by 
the  pressure  of  the  air  or  vapour  on  the  finger,  the  latter 
being  urged  away  from  the  tube  by  a  force  proportionate  to 
the  degree  of  heat  above  the  boiling  point,  and  being  drawn 
inwards  when  the  heat  is  below   that  point.     Generally, 
therefore,  the  finger  alone  will  serve  to  ascertain  whether 
the  temperature  is  above  or  below  the  point  of  ebullition; 
but  as  the  force  required  is,  after  operating  for  some  time  at 
high  pressures,  such  as  to  diminish  the  sensibility  of  the  fin- 
ger to  smaller  pressures,  it  sometimes  happens  that  on  lower- 
ing the  temperature,  the  period  at  which  it  attains  that  of 
ebullition  in  the  atmosphere  cannot  be  distinguished.     This 
point  is,  however,  easily  recognized  by  relieving  the  pressure 
of  the  finger  slightly;  should  the  quiescent  fluid  below  then 
burst  into  ebullition,  it  is  a  proof  that  its  temperature  is  higher 
than  the  boiling  point  at  atmospheric  pressure,  but  should  it 
remain  quiescent  until  the  finger  is  entirely  removed,  its 
temperature  will  be  known  to  be  below  that  point. 

922.  During  long  digestions,  as  in  the  solution  of  diffi- 
cultly soluble  bodies,  a  tube  bent  into  the  form  represented 
in  the  figure  is  very  advantageous.     The  acid  or  other  fluid 

which  is  volatilized,  and  distilled  over 
into  the  part  at  6,  is  easily  returned 
upon  the  substance  at  a,  by  elevating 
the  open  end  of  the  tube,  and  is  made  to  re-act  upon  it ;  a 
little  piece  of  moistened  paper  may  be  applied  at  6,  or  that 
part  may  be  cooled  by  a  refrigerating  mixture,  or  by  immer- 
sion in  water.  This  arrangement  is  most  frequently  useful 
in  the  solution  of  substances  but  slowly  acted  upon  in  acids, 
as  certain  metals  or  metallic  ores. 

923.  The  above  process  also  illustrates  the  use  of  tube- 
apparatus  in  distillation,  the  part  a  answers  to  the  retort,  and 
the  part  6  to  the  receiver  of  the  usual   apparatus  (447). 
The  fluid  to  be  purified  or  distilled  may  be  poured  into  the 
tube,  and  the  latter  being  held  upright,  and  the  finger  placed 
over  the  aperture,  heat  should  be  applied  below  and  vapour 


TUBE-CHEMISTRY —  RETORT RECEIVER.  4 1 9 

raised ;  this  will  condense  upon  the  sides  of  the  tube  and 
flow  down,  carrying  with  it  that  portion  of  the  fluid  which, 
in  pouring,  adhered  to  the  side ;  this  should  be  done  till  it  is 
observed  that  the  vapour  rises  nearly  to  the  top  before  it 
condenses,  and  insures  the  cleansing  of  the  whole  tube. 
This  preliminary  operation  is  intended  simply  to  wash  the 
adhering  portion  of  the  introduced  fluid  to  the  bottom  of  the 
apparatus,  that  nothing  may  remain  at  b  to  contaminate  the 
distilled  products.  The  tube  is  then  to  be  placed  as  in  the 
figure,  the  proportion  of  the  vessel  and  the  charge  being 
such,  that  the  latter  shall  not  occupy  more  than  half  that 
part  of  the  tube.  Heat  being  then  gradually  applied  near 
the  top  of  the  fluid,  the  latter  should  be  distilled  over  into 
the  angle  at  6,  which  is  now  to  be  cooled  by  wet  paper, 
water,  or  some  other  means.  If  the  distillation  be  unsatis- 
factory, it  is  easy  to  return  the  product  and  repeat  the  op- 
eration;  if  satisfactory,  then  by  applying  a  file  at  c  (1152) 
the  tube  is  readily  divided,  and  the  rectified  portion  obtained 
in  the  bent  part,  constituting  a  separate  vessel. 

924.  Distillation  is  frequently  performed  in  a  tube-appa- 
ratus, precisely  similar  to  the  ordinary  retort  and  receiver. 
A  piece  of  tube  sealed  at  one  end,  and  then  bent  as  in  the 
figure,  forms  what  is  called  a  tube- 
retort  (1175).  Fluid  substances  are 
easily  introduced  into  it  through  a 
little  tube  funnel,  made  by  heating  the  middle  of  a  piece  of 
tube  about  two  inches  long,  and  half  an  inch  in  diameter, 
by  the  lamp,  and  then  drawing  it  out  into  a  capillary  tube  and 
separating  it  of  a  proper  length  (1176,  1181).  A  receiver 
for  such  a  retort  is  made  of  a  piece  of  straight  tube  of  lar- 
ger diameter  closed  at  one  end  (911).  The  beak  of  the 
tube-retort  is  merely  inserted  an  inch  or  more  into  the  tube- 
receiver,  the  junction  is  left  open,  and  the 
latter  is  cooled,  if  required,  in  any  of  the 
usual  ways  (447,  453,  &c.).  Occasion- 
ally it  is  advantageous  to  draw  out  the 
beak  of  the  retort  into  a  capillary  form,  as 
has  been  before  described  (463,  1179); 


420  VARIETY  OF  TUBE-RETORTS  AND  RECEIVERS. 

it  will  then  enter  into  vessels  having  small  apertures  and 
necks.  Sometimes  it  is  very  useful  to  contract  the  necks 
of  tube-receivers  in  a  similar  manner,  as  will  hereafter  be 
more  evident  (929). 

925.  When  a  larger  tube-retort  is  made  use  of,  it  is  often 

useful  to  draw  out  and  contract  the 
neck,  for  the  purpose  of  diminishing 
its  capacity,  and  consequently  the 
quantity  of  vapour  which  it  can  con- 
tain; a  common  narrow-necked  phial  then  makes  an  excel- 
lent receiver. 

926.  The  tube-receiver  is  frequently  varied  in  form  with 
advantage,  by  making  it  of  a  bent  piece  of  tube  open  at 
both  ends,  and  when  one  end  of  it  is  formed  as  at  6  in  the 
following  figure,  it  is  exceedingly  convenient  for  pouring 

out  minute  portions  of  the  liquid  contained 
in  it  without  waste;  for  by  bringing  the 
small  extremity  b  against  a  glass  rod  or  a 

plate,  and  inclining  the  receiver,  as  little  or  as  much  of  the 

fluid  may  be  delivered  as  is  required. 

927.  These  tubular  vessels  may  be  supported  with  facility, 
sometimes  upon  the  table  across  two  or  three  pieces  of  glass 
tube,  or  rod,  or  upon  listed  rings  (68),  or  in  the  air  upon  the 

edge  of  glasses  placed  side  by  side,  or 
upon  retort  stands.  The  arrangements 
are  so  simple  that  no  difficulty  can  oc- 
cur with  respect  to  them.  The  receiv- 
ers may  be  cooled  by  wet  paper,  or  by  placing  them  in  water 
in  a  glass  or  Wedgwood's  dish,  or  by  putting  them  into  a 
hole  in  a  piece  of  ice,  into  which  a  little  salt  may  be  occa- 
sionally introduced  (454). 

928.  In  cases  of  distillation  upon  a  small  scale,  where,  be- 
sides a  fluid  product,  a  gas  is  also  expected  and  required  to 

be  collected  (746,  &c.),  the 

tu^e  mav  nave  tne  accompany- 
ing form  given  to  it.  If  it  be 
required  to  distil  the  first  product  a  second  time  for  its  fur- 
ther purification,  it  should  at  first  be  distilled  into  a  receiver  of 


TUBE  CHEMISTRY RECEIVERS.  421 

the  second  form,  and  that  operation  finished,  the  retort  is  to  be 
removed,  a  small  flame  applied  by  the  blow-pipe  to  the  narrow 
part  of  the  receiver  at  a,  which,  when  soft,  is  to  be  drawn  out 

andsealed  hermetically(l  167, 
1190).  The  second  rectifica- 
tion is  to  be  made  either  by 
aPPtying  heat  to  6,  and  plac- 
ing another  receiver  at  c,  or, 

by  turning  the  tube  into  the  position  it  would  take  if  this 
page  were  inverted,  applying  heat  at  a,  and  distilling  into  the 
bend  at  d. 

929.  A  very  convenient  vessel,  answering  the  purpose  both 
of  receiver  and  bottle,  may  be  made  of  tube.  For  this  pur- 
pose a  piece  of  tube,  about  the  third  of  an  inch  in  diameter, 
four  inches  long,  and  sealed  at  one  end,  is  to  be  softened  in 
a  flame  at  about  an  inch  from  the  open  extremity,  and  when 
uniformly  heated  all  round,  it  is  to  be  removed  from  the 
flame  and  drawn  out,  so  as  to  form  a  long  narrow  neck 
(1176).  The  substance  to  be  distilled  into  it,  such  as  sul- 
phurous acid  (461,  924),  or  chloride  of  phosphorus,  is  to  be 
conducted  by  a  fine  tube,  similar  to  that  already  described 
(463,  924),  which  is  to  terminate  the  distillatory  apparatus, 
being  either  drawn  out  upon  the  end  of  the  retort  or  joined 
with  it  by  a  caoutchouc  connecter  (449).  When  sufficient 
fluid  has  been  distilled  into  the  receiver,  the  capillary  neck 
ea  the  of  distillatory  apparatus  should  be  with- 

l  /  c      drawn,  the  tube  softened  about  a  by  a  small 

flame  drawn  off,  so  as  to  leave  the  termination 
there  with  a  fine  aperture  ;  then  it  is  to  be 
softened  again  at  6,  and  bent  as  in  the  second 
figure.  The  aperture  at  c  is  easily  closed 
by  holding  it  for  a  moment  in  the  edge  of 
a  flame,  and  the  contents  of  the  vessel,  how- 
ever valuable  they  may  be,  are  securely  re- 
tained. When  a  portion  is  wanted  for  ex- 
periment, the  extreme  point  should  be  nip- 
ped off  so  as  to  make  an  aperture,  and  the  tube  should  be 
inclined  until  b  becomes  the  highest  part;  so  much  of  the 


422        TUBE-RECEIVERS THEIR  USE REFRIGERATION. 

fluid  as  may  be  required  should  be  thrown  by  a  little  agita- 
tion into  the  neck  about  6,  where  it  will  remain  in  a  short 
column  ;  but  by  applying  the  hand  to  the  thicker  part  of  the 
tube,  the  air  will  expand  and  force  out  the  fluid  in  the  neck; 
on  to  any  spot  to  which  the  aperture  at  c  may  have  been 
directed.  In  this  manner  the  smallest  quantity  of  the  fluid, 
or  the  whole,  may  be  used  at  once  ;  and  enough  having  been 
removed,  the  tube  is  again  to  be  placed  in  a  more  upright 
position,  its  extremity  sealed,  and  the  whole  put  aside  until 
again  wanted. 

930.  These  receivers  are  very  useful  for  retaining  valuable 
and  volatile  fluids,  and  are  the  best  that  can  be  used   for 
such  bodies  as  sulphurous  acid  (461).     If  that  substance  be 
confined  in  ordinary  bottles,  a  great  quantity  is  suddenly 
volatilized  each  time  the  bottles  are  opened,  and  from  the 
instantaneous  cold  produced,  the  bottoms  generally  break 
and  fall  out :  but  if  it  be  preserved  in   vessels  like  those 
described,  they  may  be  of  sufficient  thinness  to  bear  this 
sudden  depression  of  temperature  without  fracture,  and  may 
even  be  cooled  previously  with  facility  by  a  piece  of  ice  and 
a  little  salt  (487,  927).      Sulphurous  acid  may  be  preserved 
in  such  tubes  in  small  portions  for  single  experiments,  or  if 
in  large  quantity,  it  is  easy  to  distil  or  transfer  it  as  has  been 
described.     When  used  for  sulphurous  acid,  they  must  of 
course  be  retained  in  a  refrigerating  mixture  during  the  dis- 
tillation (454),  they  must  be  continued  in  this  mixture  whilst 
the  top  piece  is  withdrawn  (929),  and  also  whilst  the  bend  is 
given  to  them,  if  that  be  required.     It  is  also  necessary  that 
they  be  sealed  when  thus  cooled,  for  it  cannot  be  done  after 
they  are  exposed  to  the  air  (1189,   1191,   &c.).     The  best 
method  is  to  prepare  the  small  aperture  by  drawing  off  the 
extremity,  to  lift  the  tube  into  the  air,  then  to  apply  the  flame 
of  the  lamp,  which  will  not  as  yet  seal  it,  and  afterwards  to 
lift  up  the  freezing  mixture,  or  depress  the  tube  in  it,  still 
applying  the  flame  of  the  lamp :  as  the  cold  condenses  the 
internal  vapour  the  current  outwards  will  cease,  and  the  ex- 
tremity will  close  ;   instantly  withdraw  the  lamp  so  that  the 
glass  shall  harden,  and  then  the  receiver  may  be  taken  out 
of  the  cold  mixture,  and  preserved  in  a  glass  or  tumbler 


TUBE- CHE  MIS  TRY RECTIFICATION.  423 

(911),  in  a  place  at  ordinary  temperature.  Should  there  be  a 
doubt  of  the  sealing  being  perfect,  bring  a  little  ammonia 
near  the  extremity ;  if  no  fumes  are  produced  all  is  secure, 
if  there  be  fumes  the  same  operation  of  sealing  as  that  just 
described  must  be  resorted  to. 

931.  Successive   rectifications  may  be  made  in  the  same 
tube,   by  bending  it  with  several  angles  as  in  the  annexed 
figure  ;  such  an  apparatus  was  found  of  great  service  in 
experiments  upon  the  fluids  obtained  by  the  compression 
of  oil  gas.     The  fluid  is  to  be  introduced  at  the  open  ex- 
tremity a,  so  as  to  lie  in  the 
angle   6,    then  applying  a 
small  blow-pipe  flame,  the 

glass  should  be  softened  at  the  neck,  drawn  out  and  sealed, 
the  capillary  termination  at/  being  open.  On  moderately 
heating  b  and  cooling  c,  a  distillation  of  the  more  volatile 
part  will  take  place,  the  latter  collecting  at  c ;  after  a  time, 
by  keeping  b  and  c  warm  and  cooling  d,  a  rectification  of 
the  product  at  c  may  be  effected,  and  this  distillation  may 
be  again  repeated  upon  the  product  aid  by  condensing  in  e. 
By  forming  the  angles  of  the  tube  as  in  the  figure,  the  re- 
sults may  be  returned  and  redistilled  ;  for  upon  raising  the 
end/,  the  product  in  c  will  first  return  to  &,  then  that  in  d, 
and  finally  that  in  e :  so  that  if  the  substance  be  sufficiently 
freed  from  the  denser  parts  only  after  the  third  or  fourth 
distillation,  the  products  in  c  and  d  may  be  returned  to  b 
and  redistilled  as  before,  that  in  e  being  retained  separate  : 
during  such  experiments  e  should  be  preserved  very  cold. 

932.  In  experiments   with  the  oil  gas  liquor,  distillations 
of  this  kind  were   often  to  be   performed   in  close  vessels, 
that  dissipation  of  the  more  volatile  parts  might  be  prevented. 
In  such  cases  after  having   introduced  the  fluid  to  6  and 
sealed  the  end   a,  the  end  of/   was  raised  till  it  was  the 
highest  point,  the  fluid  in  the  lower  extremity  heated  until 
combustible  vapour  issued  at  /,  and  then  a  small  flame  ap- 
plied whilst  the  temperature  of  the  other  parts  was  allowed 
to  fall ;  the  vapour  within  soon  condensed,  the  extremity 
was  instantly  closed  by  the  lamp,  the  lamp  itself  removed, 
and  the  tube  left  hermetically  sealed.     Then  collecting  all 


424  DISTILLATION  IN  VACUO. 

the  fluid  to  the  end  6,  the  distillations  and  rectifications  were 
performed,  and  when  fluid  had  collected  in  e,  it  was  easy  by 
opening  the  end/  under  mercury,  to  ascertain  whether  it 
was  sufficiently  volatile  to  rise  as  gas  at  ordinary  pressure, 
and  when  it  did  so  the  gas  was  collected  in  jars  with 
facility. 

933.  It  will  be  unnecessary  to  refer  minutely  to  the  capa- 
bility of  transferring  backwards  afforded  by  different  in- 
clinations of  the  parts  of  the  tubes :  by  angles  different  to 
those  mentioned,  the  fluid  may  be  first  returned  from  e  to  d, 
then  from  d  to  c,  and  so  on.  By  bending  the  tube  at  Z,  as 
is  represented  in  the  accompanying 
\^v  wood-cut,  so  that  the  tube  from  /  to 

^^^==k\  yc\  fit?  n  sna^  ke  *n  a  plane  perpendicular 
to  that  which  includes  the  part  from 
g  to  Z,  the  power  is  obtained  of  re- 
turning the  products  from  k  to  h,  or  from  m  to  k  inde- 
pendently of  each  other  ;  and  thus  the  more  fixed  and  more 
volatile  parts  may  both  be  returned  and  re-distilled  with- 
out mutual  interference.  The  student  will  easily  compre- 
hend these  forms  of  tubes  and  their  advantages  by  bending 
a  piece  of  wire  into  the  directed  or  desired  shape,  and  ob- 
serving the  position  of  its  parts  as  he  inclines  it  in  different 
directions. 

934.  Valuable  volatile  substances  are  frequently  purified 
with  great  advantage  by  distillation  in  vacuo  in  tube-retorts. 
A  common  tube-retort  (924)  is  to  be  softened  and  drawn  out 
near  the  open  end,  like  the  extremity  a  of  the  figure,  page 
421,  the  fluid  is  to  be  introduced,  the  neck  to  be  drawn  off 
by  a  small  flame,  and  a  minute  aperture  left  ready  for  sealing 
(929);  the  retort  being  held  with  this  aperture  upright,  the 
substance  below  is  to  be  heated  till  the  tube  is  full  of  vapour 
(932),  and  the  aperture  sealed  as  before  described  (1190). 
When  the  tube  is  cold,  the  substance  is  to  be  collected  to 
one  end,  and  the  distillation  effected  either  by  raising  its 
temperature  or  by  cooling  the  opposite  extremity.  When 
the  distillation  is  to  be  slow,  the  difference  of  temperature 
thus  caused  between  the  two  ends  should  be  slight,  when 
quick,  it  must  be  greater.  A  very  convenient  method  in 


SUBLIMATION CONDENSATION.  425 

slow  operations  is  to  pass  the  end  of  the  tube  retort  contain- 
ing the  substance  through  a  cork,  and  to 
fix  it  in  the  mouth  of  an  open  air-jar; 
this  is  to  be  supported  by  a  retort-stand 
or  two  bricks,  or  otherwise,  and  a  spirit- 
lamp  with  a  small  flame  is  to  be  placed 
under  it:  an  atmosphere  of  heated  air 
is  thus  formed  within  the  jar,  which 
warms  the  tube  more  or  less  according  to  the  arrangement, 
and  effects  the  distillation.  The  external  or  condensing  end 
of  the  tube  may  be  cooled  either  by  the  air,  or  by  water 
(447,  468),  or  by  refrigerating  mixtures  (454,  487). 

935.  The  uses  of  tubes  in  sublimation  will  be    evident 
from  what  has  been  already  said  of  that  process  (495),  and 
of  their  application  to  distillation.     Any  volatile  body,  as 
camphor,  calomel,  &c.,  placed  at  the  bottom  of  a  straight 
tube  closed  at  the  lower  end  and  heated,  will  sublime  and 
condense  in  the  cooler  upper  part;  after  which  the  tube  may 
be  cut  with  the  utmost  facility  (1152)  between  the  sublime 
part  and  the  residuum,  and  the  former  obtained  in  a  pure 
state. 

936.  In  these  operations  the  successful  condensation  of 
the  vapour  is  materially  influenced  by  several  little  circum- 
stances requiring  attention:  these,  when  the  substance  is  easily 
condensed,  and  the  upper  part  of  the  tube  is  retained  suffici- 
ently cool  bymere  contact  of  the  air,  relate  simply  to  position. 
The    nearer    the   tube  is  held  to    a  vertical    position,  the 
greater  will  be  the  length   heated  by  the  ascending  flame, 
and  on  the  contrary,  the  nearer  to  a  horizontal  position,  the 
less  wil  be  the  extent  thus  elevated  in  temperature.     Advan- 
tage may  be  taken  occasionally  of  both  these  circumstances. 
In  subliming  cinnabar,  arsenic,  calomel,  or  any  other  body 
requiring  a  high  heat  for  the  formation  of  its  vapour,  the 
vertical  position  of  the  tube  is  the  best,  the  place  of  conden- 
sation being  then  farther  removed  from  the  place  where  the 
crude  substance  lies,  and  the  crystals  themselves  being  better 
formed  in  consequence  of  the  vapour  losing  its  high  temper- 
ature less  rapidly;  but  with  such  substances  as  iodine,  naph- 

3D 


426  SUBLIMATION CONDENSATION 

thaline,  camphor,  corrosive  sublimate*,  and  bodies  whose 
vapours  are  either  formed  at  low  temperatures,  or  which 
condense  into  a  liquid  before  solidifying,  the  position  of  the 
tube  should  be  nearly  horizontal,  that  the  place  of  condensa- 
tion may  not  be  too  much  heated  for  its  office,  nor  so  inclined 
as  to  occasion  the  immediate  descent  of  the  portion  of  fluid 
condensed  there. 

937.  Occasionally  it  will  even  be  necessary  to  cool  the  place 
of  condensation;  this  may  be  done-by  a  damp  finger,  or  by  a 
piece  of  tin  or  copper  foil  wrapped  round  it  (1356),  or  by  a 
slip  of  wet  paper  folded  over  it  (447)  and  moistened  from 
time  to  time.     A  very  convenient  and  useful  method  of  con- 
densation, when  it  is  required  quickly  to  remove  a  portion  of 
the  substance  out  of  the  subliming  vessel,  is  to  introduce  the 
end  of  a  smaller  tube,  closed  below,  and  containing  a  little 
water,  into  the  subliming  vessel.    But  this  must  be  done  only 
with  such  substances  as  rise  at  low  temperaturesand  condense 
readily,  for  example,  iodine,  camphor, naphthaline,  &c.;  for  if 
very  hot'vapours,  as  those  of  mercury,  were  to  come  in  con- 
tact with  such  a  cooled  tube,  they  would  probably  break  it, 
and  cause  inconvenience  from  the  dispersion  and  mixture  of 
the  water.     The  substance  condenses  on  the  exterior  of  the 
introduced  tube,  and  may  be  withdrawn  with  it.     A  tube 
filled  with  mercury  may  be  used  for  condensation  in  a  similar 
way,  or  even  a  cold  glass  or  metal  rod;  but  the  condensation 
should  in  these  cases  never  be  continued  so  long  asto  heat  the 
rod,  or  the  condensing  tube  and  its  contents,  very  highly,  for 
then  their  efficacy  fails.     If  they  become  hot,  they  should  not 
be  withdrawn  in  that  state  with  the  substance  upon  them,  but 
their  temperature  first  allowed  to  descend  so  as  not  to  occasion 
volatilization,  or  serious  loss  of  the  substance,  when  brought 
into  the  open  air. 

938.  Sublimation  may  frequently  be  effected  very  simply 
and  conveniently  by  condensing  the  vapours  in  a  tube  placed, 
not  within,  but  over  the  subliming  vessel,  a  short  but  larger 
one  being  inverted  over  the  mouth  of  the  latter,  and  the  con- 
densation taking  place  principally  in  it.     In  place  of  this 
second  tube  a  flask  or  phial  may  be  used.,    A  very  conve- 
nient form  of  condensing  tube  for  heavy  vapours,  or  easily 


SUBLIMING  IN  TUBES — BERZELIUS5  MODE.  427 

fusible  substances,  as  iodine,  naphtha- 
line, &c.,  is  that  of  the  annexed  figure, 
the  bent  tube  being  of  such  diameter  as 
freely  to  pass  over  the  subliming  tube, 
but  not  larger;  the  condensation  takes 
place  principally  in  the  upper  part  of  the  middle  portion  of 
the  tube,  and  the.  refrigeration  may  be  effected  in  the  most 
convenient  manner  either  by  moist  paper  or  immersion  in 
water  (447). 

939.  Berzelius  has  upon  particular  occasions  used  an  open 
tube  for  sublimation,  the  length  being  about  six  inches,  the 
diameter  half  an  inch  or  more,  and  the 
position  an  inclined  one.  When  a  sub- 
stance is  heated  in  the  lower  part  of  the 
tube,  an  upward  current  of  air  carries 
the  vapours  forward  into  the  cooler  part,  where,  if  conden- 
sable under  the  existing  temperature  and  circumstances,  they 
assume  the  liquid  or  solid  form.  The  air  has  access  to  such 
a  tube  or  may  be  shut  out  by  the  finger  at  pleasure,  and  any 
combustible  body  heated  in  it  may  consequently  be  burnt 
if  required;  this  circumstance  occasioned  the  introduction  of 
the  tube  into  use.  A  crude  mixture  containing  much  sul- 
phur with  a  little  selenium,  being  put  into  the  lower  part  and 
heated,  the  sulphur  inflamed,  and  forming  sulphurous  acid, 
passed  away;  the  selenium  sublimed,  and  condensed  in  part  in 
the  upper  portion  of  the  tube,  and  a  fixed  impurity  remained 
in  the  place  of  the  mixture.  The  portion  of  selenium  might 
afterwards  be  sublimed  or  otherwise  examined,  and  many  of 
its  properties  ascertained.  It  is  in  the  continually  varying  ex- 
periments of  investigations  and  research,  that  such  practices 
and  facilities  as  these  are  resorted  to.  They  are  found  of 
essential  advantage  where  the  object  is  rather  to  effect  the 
separation  of  bodies  supposed  to  be  present,  with  a  volun- 
tary loss  of  part,  than  merely  to  purify  one  substance  from 
another  in  such  manner  as  to  preserve  the  whole.  Both 
objects  are  important  in  turn,  and  both  may  be  attained  by 
one  or  other  of  the  processes  and  practices  described. 

940.  Tubes  are  exceedingly  convenient  for  the  heating  or 
even  igniting  of  numerous  substances,  in  the  vapours  of  vola- 

• 


428  BODIES  HEATED  IN  VAPOURS. 

tile  bodies,  which  are  either  solid  or  fluid,  at  common  tempe- 
ratures. If  a  small  piece  of  naphthaline  be  put  into  a  tube 
closed  at  one  end,  and  held  in  an  inclined  position,  and  the 
bottom  be  heated,  the  naphthaline  will  melt,  sublime, condense 
above,  and  descend  to  the  lower  end  in  a  stream;  but  as  soon 
as  it  reaches  the  hot  part  it  will  be  re-volatilized,  to  be  re-con- 
densed above,  and  to  flow  down  as  before.  In  these  circum- 
stances the  bottom  of  the  tube  maybe  heated  red-hot  for 
half  an  hour  or  longer,  being  filled  during  the  whole  time 
with  the  vapour  of  naphthaline  nearly  pure.  The  same  may 
be  effected  by  a  little  management,  easily  to  be  acquired  by 
practice,  with  alcohol  or  ether,  or  sulphur,  or  even  iodine, 
and  indeed  with  a  numerous  setof  important  chemical  agents. 
It  will  be  evident,  that  any  fixed  substance  placed  in  the  bot- 
tom of  the  tube,  may,  under  these  circumstances,  be  heated 
to  redness  for  a  long  time  in  the  vapour  of  the  volatile  body, 
and  thus  the  facility  of  acting  on  metals,  metallic  oxides, 
and  other  bodies,  by  such  agents  as  those  mentioned  above, 
is  obtained.  Nor  is  it  confined  to  these  cases,  for  the  vapour 
of  sulphur,  for  instance,  may  be  heated  to  redness,  mixed 
with  the  vapour  of  ether  or  of  naphthaline;  or  these  latter  sub- 
stances may  be  raised  to  a  red  or  a  white  heat,  for  the  pur- 
pose of  effecting  their  decomposition;  and  a  great  variety  of 
important  experiments  may  be  thus  performed,  to  the  full 
satisfaction  of  the  experimenter. 

941.  Those  who  work  much  with  tube-apparatus  will  have 
frequent  occasion  to  dry  precipitates  or  powders  contained 
in  tubes,  or  even  to  evaporate  fluids  to  dryness  in  them. 
These  processes  may  be  performed  with  more  facility  than  is 
generally  imagined,  but  require  peculiar  though  easy  ar- 
rangements and  precautions.  Suppose,  as  the  simplest  case, 
that  a  portion  of  moist  powder,  a  precipitate  for  instance, 
contained  in  a  tube,  is  to  be  dried:  a  paper  handle  should 
first  be  adapted  to  the  tube  (918),  and  then  heat  applied  to 
volatilize  the  water.  The  first  portionsof  vapour  vvillcondense 
on  the  interior  of  the  tube  and  form  drops,  which  descending 
may  sometimes  cause  the  fracture  of  the  hot  glass  below; 
to  prevent  this  the  tube  is  to  be  held  in  a  position  nearly 
horizontal,  so  that  the  drops  shall  have  but  little  tendency 


TUBE-CHEMISTRY DESICCATION.  429 

to  descend,  and  a  piece  of  filtering  paper  is  to  be  folded 
lengthways  and  introduced  into  the  tube,  as  far  as  the  com- 
mencement of  that  part  is  too  hot  to  permit  of  condensation. 
This  piece  of  paper,  lying  upon  the  lower  internal  surface  of 
the  tube,  is  sufficient  to  absorb  all  the  liquid  that  may  con- 
dense, and  does  not  interfere  with  the  passage  outwards  of 
that  part  of  the  water  which  is  still  in  the  state  of  vapour. 
When  all  the  water  is  driven  from  the  substance,  the  paper 
may  be  withdrawn,  bringing  away  the  moisture  with  it. 

When  the  desiccation  is  performed  in  long  tubes,  it  is  ad- 
vantageous to  wrap  paper  or  tow  round  the  upper  part,  to 
keep  them  hot,  and  prevent  as  much  as  possible  the  conden- 
sation of  the  vapour.  When  from  any  circumstance  a  drop 
has  collected  in  the  upper  part  of  a  tube,  and  is  in  danger 
of  running  down  and  causing  injury,  either  by  cracking  the 
glass  or  by  its  chemical  action,  it  may  readily  be  removed 
by  bringing^the  end  of  a  piece  of  folded  or  rolled  bibulous 
paper  into  contact  with  it. 

942.  When  the  contents  of  tubes  have  been  thus  dried, 
the  tubes  themselves  are  often  left  filled  with  aqueous  va- 
pour, and  their  sides  in  a  damp  state.  But  these  small  por- 
tions of  water  are  easily  removed  whilst  the  tube  is  warm, 
either  by  blowing  or  drawing  air  through  it.  For  this  pur- 
pose one  end  of  a  long  narrow  tube  is  to  be  introduced, 
the  mouth  applied  to  the  other  end,  and  air  blown  through 
it;  this  will  rapidly  take  up  the  warm  water,  and  carry  it 
out  into  the  atmosphere.  Still,  however,  the  tube  remains 
filled  with  air  from  the  lungs,  which,  being  in  a  moist  state, 
would,  on  the  falling  of  the  temperature,  cause  a  dampness 
and  deposition  ;  to  prevent  this  a  portion  of  air  is  to  be 
drawn  by  the  mouth  through  the  long  narrow  tube  before  its 
removal,  which  air,  as  it  must  previously  have  entered  into 
the  outer  tube  from  the  surrounding  atmosphere,  will  effec- 
tually remove  all  portions  of  that  from  the  mouth  which  had 
been  left  there.  This  process  of  drawing  the  air  of  the  at- 
mosphere through  vessels,  is  a  very  ready  and  useful  expedi- 
ent in  many  cases  where  vessels  are  to  be  dried,  but  it 
should  never  be  resorted  to  if  any  deleterious  vapours  or 
gases  are  present,  as  they  are  then  conveyed  into  the  lungs: 


430  TUBE-PNEUMATICS TUBE-RETORT. 

a  pair  of  bellows  should  on  such  occasions  be  used  to  propel 
the  air. 

943.  When  a  comparatively  large  quantity  of  water  is  to 
be  evaporated  from   tubes  upon  the  sand-bath,  at  tempera- 
tures below  ebullition,  it  is  ordinarily  a  very  slow  process, 
in  consequence  of  the  limited  access  of  air  to  the  interior 
(591),  except  some  expedient  be  adopted  to  facilitate  its  en- 
.  trance  and  exit.     A  very  generally  convenient  one  is  to  in- 
sert one  end  of  an  open  bent  tube,  as  in  the  figure;  a  cur- 
rent of  air  is  thus  established  either  in 
the  one  direction  or  the  other,  and  the 
aqueous   vapour   readily  removed.      A 
more  convenient  evaporator   is  a  bent 
tube  open  at  both  ends,  as  in  the  an- 
nexed  figure,  which    being  set  in  the 
sand-bath,  or  otherwise  heated,  so  as  to 
have  one  limb  rather  holier  than  the 
other,   has  a  current  spontaneously  es- 
tablished through  it.     The  evaporation  proceeds  with  readi- 
ness and  facility  ;  the  dry  results  are  very  easy  of  access,  and 
yet  little  danger  of  their  dispersion  during  the  process  is  in- 
curred. 

944.  With  reference  to  tube  pneumatic  apparatus,  the 
advantages  which  it  supplies  to  those  who  know  how  to  use 
it  are  equally  great  with  other  applications  of  tubes  in  the 
construction  of  apparatus.     It  is  surprising  to  observe  how 
many  of  the  ordinary,  and  even  refined,  experiments  of  mod- 
ern pneumatic  chemistry  may  be  repeated  satisfactorily  with 
an  evaporating  basin  for  a  pneumatic  trough,  and  with  re- 
torts, receivers,  and  other  vessels,  formed  of  tubes  (728,  &c). 

945.  The  tube-retort  has  been   already  described  (924), 
and  the  modification  produced  by  drawing  out  the  neck  after 
having  introduced  the  material  has  been  referred  to  (924). 
This  variation  is  often  of  great  service:  thus  if  an  oxide  of 
silver  or  of  mercury  were  to  be  decomposed  by  heat,  and  the 
gas  ^collected,  it  would  be  advisable  to  put  it  into  a  piece 
of  straight  tube  closed  at  one  end,  and  then  applying  heat 
above  the  containing  part,  to  draw  the  tube  out  into  a  nar- 


TUBE  AIR-JARS  —  OXYGEN EUCHLORINE.  431 

row  neck  (925)  from  four  to  six  inches  in  length  ;  this  should 
be  bent  near  to  the  body,  by  holding  it  over  the  flame  of  a 
small  spirit-lamp.  Such  a  retort  approaches  more  closely 
in  its  form  to  the  ordinary  vessel  than  the  common  tube  re- 
tort, and  it  will  be  useful,  not  merely  in  the  instances  men- 
tioned, but  in  most  cases  where  the  materials  are  solid,  and 
remain  so,  or  do  not  swell  much,  during  the  action  of  heat 
upon  them. 

946.  Tube  air-jars  or  receivers  are  merely  tubes  closed  at 
one  end,  and  cutoff  level  at  their  mouths  (1152).     They 
may  be  long  or  short,  plain,  or  graduated.     Funnels  for  the 
transference  of  liquids  into  retorts,  or  gas  into  tubes  over 
water  or  mercury,  are  easily  made  of  a  piece  of  wide  tube, 
as  before  described  (924).     An  evaporating  basin  filled  with 
water  makes  an  excellent  trough;  it  should  have  a  slip  of 
heavy  metal,  such  as  sheet  lead,  laid  at  the  bottom,  against 
which  the  mouths  of  the  tube  receivers  may  rest,  whilst  they 
recline  above  against  the  side  of  the  basin.     The  tubes  are 
thus  prevented   from  slipping  to  the   bottom,  or  changing 
their  inclined  and  proper  position  for  a  horizontal  one,  which 
would  endanger  the  loss  of  gas. 

947.  Oxygen,  a  small  quantity  of  which  in  a  pure  state  is 
often  required,  is  conveniently  and  economically  made  even 
in  the  large  and  well  furnished  laboratory,  from  chlorate  of 
potash,  in  a  tube  retort.     Euchlorine  is  generally,  if  not  al- 
ways, best  made  in  a  tube  retort,  but  then  another  variation 
is  advantageous,  which  is  useful  also  in  numerous  other  cases. 
The  retort  itself  is  to  be  a  piece  of  plain  tube,  about  half 
an  inch  in  diameter,  two  or  three  inches  in  length  according 
to  circumstances,  and  closed  at  one  end  :  the  mouth  is  to  be 
fitted  with  a  good  perforated  cork,  having  a  small  tube  fixed 
into  it,  which,  after  proceeding  about  an  inch  upwards  from 
the  cork,  is  to  turn  off  nearly  at  right  angles  for  about  three 
inches,  and  then  return  to  its  first  direction  for  about  the 
eighth  of  an  inch.     This  piece  of  tube  is  the  neck  of  the 
retort,  whilst  the  wide  short  piece  is  the  body ;  and  the  lat- 
ter having  received  its  charge,  the  cork  is  to  be  put  in  and 
made  tight  by  soft  cement,  after  which  the  distillation  may 
be  proceeded  with,  and  the  gas  evolved  and  collected. 


432  TUBE MERCURIAL  RECEIVER. 

948.  In  reference  to  the  distillation  of  euchlorine,  and  of  all 
other  explosive  substances,  the  student  should  be  aware  of 
the  caution  required  to  prevent  accidents,  in  case  explosion 
should  occur.     Whenever  such  an  effect  is  probable,  the 
vessel  should  be  surrounded  with  tow  or  cloth,  that  if  it 
break  the  fragments  may  be  retained ;  and  during  distilla- 
tion the  side  of  the  apparatus,  or  that  part  which  is  guarded 
by  the  tow,  is  to  be  turned  towards  the  eyes,  that  they  at 
least  may  be  out  of  danger.     It  is  not  easy  to  wrap  tow 
regularly  and  tightly  round  a  clean  glass  tube,  from  its  ten- 
dency to  slip  over  the  surface ;  but  the  difficulty  is  obviated, 
by  rubbing  the  outside  of  the  tube  with  soft  cement,  or  a 
very  little  turpentine  with  a  piece  of  tow  or  cloth,  so  as  to 
render  it  slightly  adhesive  to  the  fingers*. 

949.  When  a  mercurial   trough  is  required,  it  may  be 
made  either  of  an  evaporating  basin,  or  an  earthenware 
crucible,  or  even  of  a  glass  or  cup,  according  to  circumstan- 
ces ;  the  first  being  most  convenient  for  transference,  the 
latter  for  collecting  gas,  delivered  from  retorts  or  tubes.    The 
apparatus  delivering  gas  should  always  be  made  to  turn  up 
at  the  end,  as  has  been  described  of  the  euchlorine  retort, 
that  the  gas  may  be  fairly  thrown  off,  and  into  the  mouth 
of  the  receiving  vessel  (947). 

950.  A  very  convenient  mercurial  receiverf  of  the  form 
represented  in  the  annexed  figure,  may  be  made  of  tube 

from  half  to  three-quarters  of  an  inch  in  diam- 
eter, and  from  four  to  ten  inches  in  length.  It  is 
closed  above  but  open  at  the  lower  extremity.  It  is 
to  be  filled  with  mercury  when  inclined,  by  pouring 
in  the  metal  at  the  mouth,  and  is  then  to  be  suspen- 
ded  or  supported  in  the  position  represented,  with 
an  evaporating  basin  beneath  it.  The  small  tube 
delivering  gas  is  to  be  introduced  at  the  mouth,  so  far  as  to 


*  Such  processes  are  most  safely  conducted  in  a  large  hollow  cylinder  of 
wire-gauze  bottomed  with  wood,  and  left  open  at  the  top.  A  wire-gauze  door 
in  the  side  is  a  convenient  addition.  When  such  an  article  is  placed  on  a  level 
with  the  face  of  the  operator,  the  processes  are  safely  conducted,  and  easily 
inspected. — ED. 

f  First  suggested,  I  believe,  by  Mr  Cooper.  i 

*'. 


TUBE  CHEMISTRY — MERCURIAL  RECEIVER.  433 

allow  the  bubbles  to  pass  into  the  tube,  and  the  mercury  to 
flow  out  into  the  basin  below.     When  the  mercury  has  de- 
scended nearly  to  the  flexure,  the  operation  should  be  stopped. 
951 .  The  gas  thus  collected  may  be  examined  as  to  a  great 
number  of  its  characters  without  the  help  of  any  other  tube, 
or  of  any  transference  but  what  may  be  obtained  by  moving 
it  from  one  part  of  the  tube  to  another.     For  instance,  the 
finger  may  be  placed  on  the  aperture,  in  contact  with  the 
metal,  so  as  to  exclude  all  air  and  close  the  mouth  of  the 
receiver;  then  inclining  the  vessel,  a  bubble  of  gas  may  be 
made  to  pass  round  the  bend  towards  the  ringer :  this  done, 
upon  restoring  the  upright  position  of  the  receiver,  the  larger 
portion  of  gas  will  still  be  in  the  upper  part,  but  a  quantity 
varying  from  a  quarter  to  three-quarters  of  an  inch  in  extent, 
according  to  the  will  of  the  operator,  will  be  confined  between 
the  mercury  and  the  ringer,  quite  unconnected  with  the  larger 
portion.     This  quantity  may  be  tried  as  to  inflammability  by 
bringing  a  lighted  taper  near  the  aperture,  and  immersing  it  in 
the  gas  the  moment  the  finger  is  removed.     Suppose  this  trial 
made  and  the  consequent  knowledge  acquired;  then  by  pour- 
ing in  mercury,  so  as  to  fill  the  small  space  now  unoccupied, 
re-applying  the  finger  and  re-inclining  the  tube,    another 
portion  of  the  gas  is  brought  into  a  situation  similar  to  the 
former;  this  may  be  examined  as  to  smell,  and  its  odorous 
or  inodorous  nature  ascertained.     Again  filling  the  space 
with  mercury,  and  repeating  the  operations  as  before,  a  third 
portion  of  gas  can  be  brought  to  the  mouth  of  the  tube,  and 
this  may  be  examined  as  to  whether  it  is  heavier  or  lighter 
than  the  atmosphere,  if  from  the  two  previous  trials  it  appeared 
to  differ  in  quality  from  common  air:  thus,  if,  after  leaving 
the  mouth  open  a  short  time,  the  atmosphere  around  being 
quiescent,  the  gas  or  a  part  of  it  still  remains  in  the  tube,  it 
must  be  heavier  than  air,  whereas  if  all  signs  of  it  have 
disappeared,  it  is  a  proof  of  its  lightness  as  compared  with 
that  standard.     In  a  similar  manner  trial  may  be  made  of  the 
solubility  of  the  gas  in  water,  by  filling  up  the  space  left  by 
the  last  experiment  with  water  instead  of  mercury,  or  at  least 
in  part  by  water,  and  then  bringing  a  bubble  of  gas  to  that 
part  as  before;  if  it  instantly  disappear,  it  indicates  conside- 
3E 


434  TUBE-CHEMISTRY MERCURIAL  RECEIVER. 

rable  solubility,  if  it  does  not  at  all  diminish,  it  shows  com- 
parative insolubility.  If  a  solution  be  actually  formed,  then 
upon  removing  the  finger  it  may  be  examined  as  to  its  acid 
or  alkaline  nature,  or  other  properties. 

952.  In  these  and  similar  experiments  great  care  should  be 
taken  that  no  water  pass  beyond  the  bend  into  the  tube,  for 
which  reason  but  little  water  should  be  put  in  at  once;  there 
should  be  sufficient  mercury  between  it  and  the  angle  to 
replace  the  bubble  of  gas  which  is  to  be  brought  to  the 
mouth,  and  the  inclination  of  the  tube  should  be  carefully 
attended  to,  that  no  water  inadvertently  pass  backward  into 
the  higher  part.     When  the  trial  of  solubility  is  over,  the 
water  should   be  taken  from  the  mouth  of  the  tube,  first  by 
a  folded  piece  of  bibulous  paper,  and  afterwards  with  tow 
upon  a  wire.   Trials  may  afterwards  be  made  with  lime-water 
or  alkaline  solutions,  their  action  upon  a  part  or  the  whole 
of  the  gas  being  in  this  way  easily  observed. 

953.  Thus  the  gas  may  be  divided  into  many  successive 
portions,  and  submitted    to    numerous    examinations;    and 
should  it  so  happen  that  a  part  is  absorbed  by  water,  and  a 
gas  left  which  could  not  be  properly  examined  whilst  in  a 
state  of  mixture,  then,  after  having  made  the  proper  experi- 
ments upon  the  mixture,  a  little  water  may  be  let  into  the 
body  of  the  receiver,  and  shaken  with  it,  to  absorb  the  soluble 
gas,  and  the  finger  being  removed  from  the  aperture,  either 
under  mercury  or  water,  those  fluids  will  enter  and  supply 
the  place  of  the  absorbed  substance.     The  insoluble  and 
purified  remainder  may    now    be    examined  in    successive 
portions,  exactly  in  the  manner  just  described. 

954.  In  numerous  cases  gas  may  actually  be  retained  and 
examined  in  the  tubes  in  which  they  have  been  generated ; 
and  no  use  of  simple  tubes  is  more  important  than  the  useful 
indications  they  furnish  when  substances  are  heated  in  them 
and  the  evolved  vapour  or  gases  examined  at  their  mouths. 
Thus  when  a  little   piece  of  animal  matter  is  heated  in  a 
small  tube,  it  is  easily  ascertained,  by  a  slip  of  turmeric  paper 
at  the  mouth  of  the  vessel,  whether  ammonia  is  evolved:  or, 
if  sulphur  be  heated  with  a  vegetable  substance,  the  appro- 
priate tests  applied  in   a  similar  manner  will  show  whether 
sulphuretted  hydrogen  gas  be  extricated.     Several   of  the 


OXYGEN CARBONIC  ACID — EUCHLORINE.  435 

properties  of  oxygen  are  exhibited  by  putting  a  little  chlorate 
of  potash  or  oxide  of  mercury  into  the  bottom  of  a  glass  tube, 
and  applying  heat  so  as  to  evolve  oxygen  ;  the  source  of  heat 
may  be  removed  after  sufficient  gas  has  been  liberated  to  fill 
the  space  above,  and  that  may  be  judged  of  in  the  one  case 
by  the  ebullition  of  the  chlorate,  and  in  the  other  by  the  ap- 
pearance of  metallic  mercury.  The  gas  may  then  be  ex- 
amined as  to  its  power  of  supporting  combustion,  and  that 
being  done,  the  impure  mixture  remaining  after  the  experi- 
ment may  be  blown  out,  and  by  a  fresh  application  of  heat 
another  portion  of  pure  gas  evolved. 

955.  Carbonic  acid  gas  may  be  examined  in  a  similar  man- 
ner in  a  tube,  at  the  bottom  of  which  is  a  piece  of  marble 
and  a  little  dilute  muriatic  acid  ;  and  so  also  may  muriatic 
acid  gas,  sulphurous  acid  gas,  chlorine,  and  euchlorine,  very 
conveniently.  Perhaps,  with  regard  to  the  latter  gas,  this  is 
the  safest  way  for  a  tyro  to  examine  its'properties.  A  little 
pulverised  chlorate  of  potash  and  strong  sulphuric  acid  should 
be  put  into  the  bottom  of  such  a  tube,  the  acid  first,  and  the 
chlorate  in  successive  small  quantities ;  euchlorine  will  gra- 
dually rise  and  fill  the  lower  part  or  the  whole  of  the  tube, 
the  gas  appearing  of  a  deep  yellow  colour*.  Occasionally 
the  liberation  may  be  hastened  by  the  warmth  of  the  hand, 
or  a  little  warm  water,  the  mouth  of  the  tube  being  directed 
from  the  operator.  By  warming  the  upper  part  of  the  tube 
with  a,  small  lamp-flame,  or  by  immersing  a  hot  wire  into  the 
gas,  its  explosive  nature  will  be  observed,  the  disappearance 
of  colour  remarked,  and  even  the  chlorine  and  oxygen  liberated 
may  be  recognised  by  their  proper  qualities.  Afterwards,  if 
a  little  more  time  be  allowed  or  warmth  applied,  a  fresh  por- 
tion of  euchlorine  will  be  evolved  from  the  materials  for 
another  experiment.  The  weight  of  the  gas  may  now  be 
observed  by  pouring  it  from  the  generating  tube  into  another 
tube,  or  a  wine-glass.  It  will  descend  through  the  air  like 
water.  Whilst  pouring,  the  air  should  be  left  undisturbed, 
and  the  tube  from  which  the  gas  flows  not  quite  inverted, 
but  raised  with  the  closed  end  only  a  little  above  the  hori- 

*  Mr  Faraday  appears  to  think  with  Mr  Brande,  that  the  euchlorine  obtained  by 
Davy  from  chlorate  of  potash  and  hydrochloric  acid,  is  not  a  definite  compound., 
and  therefore  calls  the  peroxide,  euchlorine, — ED. 


436        HARE'S  METHOD — QUADROXIDE  OF  CHLORINE. 

zontal  line.  If  apiece  of  copper  leaf  (1351)  be  put  into  the 
receiving-tube  or  wine-glass,  it  will  be  seen  that  theeuchlo- 
rine  has  no  action  upon  it,  and  if  then  the  separation  of  its 
elements  be  effected  by  touching  the  gas  with  a  hot  wire,  it 
will  also  be  seen  that  the  metal  will  burn  in  the  clorine  set 
free.  Thus  a  very  extensive  and  instructive  set  of  experi- 
ments on  this  curious  compound  may  be  made  with  no  other 
apparatus  than  tubes. 

[The  figure  represents  Dr  Hare's  method  of  forming  and 
examining  peroxide  of  chlorine,  one  so  convenient  and  ele- 
gant as  to  require  no  apology  for  its  insertion. 

"  Into  a  tube,  supported  on  a  table, 
in  a  position  inclined  from  that  in 
which  the  operator  stands,  about  an 
eighth  of  an  ounce  of  sulphuric  acid 
is  introduced.  Chlorate  of  potash  in 
powder  is  added  gradually  in  very 
small  quantities,  till  a  paste  is  formed, 
of  an  orange  colour. 

"  The  tube  being  thus  charged,  it 
is  corked  gently,  and  suspended  with- 
in the  stout  cylinder,  as  in  the  draw- 
ing. It  is  then  surrounded,  near  the 
bottom,  by  another  tube,  supplied 
with  boiling  water.  At  first,  the  hot 
water  is  applied  only  to  that  part  of 
the  tube  which  contains  the  paste  : 
but,  as  soon  as  the  inner  tube  is  per- 
vaded by  a  green  yellow  colour,  demonstrating  the  evolution 
of  the  gaseous  tritoxide,  the  outer  tube  containing  the  water 
is  to  be  raised,  so  that  the  gas  maybe  generally  heated  by  it. 
"  An  explosion  soon  follows,  from  the  influence  of  which 
spectators  are  protected,  by  the  glass  cylinder."  Hare's 
Compendium,  p.  112. — ED.] 

956.  There  are  certain  chemical  actions  which  take  place 
between  solids  and  fluids,  where  the  fluid,  from  its  price,  is 
of  no  great  consequence,  and  may  be  used  instead  of  water 
for  collecting  the  gas  evolved  during  the  action.  This  is  the 
case,  for  instance,  when  a  formiate  is  acted  upon  by  sul- 


TUBE  CHEMISTRY KERIl's  TUBE.  437 

phuric  acid  to  show  the  immediate  evolution  of  carbonic 
oxide ;  and  also  when  the  same  acid  is  made  to  act  by  heat 
upon  oxalic  acid,  to  show  the  evolution  of  carbonic  oxide 
and  carbonic  acid  :  many  similar  cases  occur.  These  actions 
may  very  conveniently  be  effected  in  a  form  of  tube  first 
described  by  Mr  Kerr*.  A  simple  tube,  closed  at  one  ex- 
tremity, is  to  be  bent  near  the  middle,  but  rather  towards 
one  end,  in  such  a  manner  that  when 
placed  as  in  the  figure,  the  vertex  on 
the  lower  side  shall  not  be  directly  un- 
der that  on  the  upper  side,  but  nearer 
the  closed  end  ;  this  is  easily  effected  during  the  bending 
by  making  one  part  softer  than  another,  or  by  blowing  it  out 
as  is  to  be  described  (1197).  The  part  from  a  to  6  being 
then  filled  with  the  sulphuric  acid  or  the  acting  fluid,  the 
substance  to  be  acted  upon  is  to  be  dropped  in  at  c,  and 
will  descend  into  the  acid  at  d.  When  the  action  commen- 
ces, either  at  common  temperatures  or  by  applying  a  little 
heat,  the  gas  formed  at  d  will  ascend  in  the  closed  limb  and 
cause  the  fluid  to  occupy  the  other.  The  experiment  should 
be  made  over  a  basin  of  water,  that  the  acid  may  occasion 
no  harm  if  a  little  should  be  spilt ;  and  when  the  tube  is  full, 
or  the  action  has  ceased,  the  acid  should  be  replaced  by  water 
or  mercury,  and  the  gas  examined.  To  replace  it  by  water, 
it  is  only  necessary  to  immerse  the  tube  in  that  fluid,  and 
then  to  raise  the  closed  end,  so  that  the  acid  may  pour  out 
of  the  tube  and  have  its  place  supplied  by  the  water  :  to  re- 
place it  by  mercury,  it  is  necessary  to  pour  mercury  into  the 
open  limb,  allowing  the  sulphuric  acid  to  flow  over,  and  also, 
if  there  be  any  portion  in  the  closed  limb  of  the  tube  in  con- 
sequence of  the  insufficiency  of  the  gas  to  fill  it,  to  displace 
it  by  inclining  the  tube  carefully,  so  that  it  may  flow  over 
the  mercury  between  it  and  the  glass  into  the  other,  or  open 

*  Edinburgh  Philosophical  Journal,  x.  53.  Mr  Kerr  has  the  merit  of  first  de- 
scribing the  utility  of  the  bent  tube  above  referred  to,  and  of  making  the  important 
improvement  in  the  position  of  the  vertices.  This  tube,  without  that  improve- 
ment, and  all  other  tubes  described  in  this  section,  except  the  modification  sug- 
gested by  Mr  Kerr  (957),  have  been  in  use  in  the  laboratory  of  the  Royal  Insti- 
tution for  many  years,  and  it  was  supposed  were  resorted  to  in  most  other  labora- 
tories of  research. 


438  KERR'S  APPARATUS. 

limb,  without  allowing  any  gas  to  follow.  In  this  way  all 
the  sulphuric  acid  may  be  removed,  except  that  portion 
which  adheres  to  the  glass,  which  may  be  cleared  away  from 
the  greater  part  of  the  open  limb  after  the  mercury  has 
been  poured  in,  by  wiping  the  glass  first  with  a  little  plug  of 
wet  tow  upon  the  end  of  a  wire,  and  afterwards  by  dry 
tow.  When  the  acid  has  been  replaced  by  water  or  mer- 
cury, the  gas  may  be  examined  in  successive  portions  in  the 
manner  already  described  (950). 

957.  Mr  Kerr  suggests  an  improvement  of  this  tube*,  by 
making  it  of  the  accompanying  figure,  with  an  aperture  at  a, 
OT  topped  with  a  ground  stopper;  or  a 
cork  covered  with  wax.     Its  use  is  the 
same  as  that  of  the  former,  but  it  af- 
fords a  further  facility  of  transferring 
a  little  gas  from  it  to  another  vessel 
without  interfering  with  the  fluid  in  the  apparatus.     As  the 
gas  collects  in  the  closed  limb,  the  small   quantity  of  fluid 
remaining  in  the  short  part  is  to  be  turned  out,  by  inclining 
the  tube,  and  this  may  be  done  safely  from  the  mutual  in- 
clination of  the  parts,  without  spilling  any  of  the  acid  at  the 
open  extremity.     When  gas  is  to  be  transferred  from  this 
vessel  to  a  separate  one,  as  a  small  tube-jar,  the  inferior  end 
of  the  descending  part  of  the  closed  branch  is  to  be  dipped 
beneath  the  surface  of  water  or  mercury,  according  to  the 
nature  of  the  gas;  and  when  the  stopper  or  cork  is  taken  out, 
the  gas  will  issue  forth,  or  may  easily  be  made  to  do  so,  by 
raising  the  extremity  more  or  less  in  the  water,  or  by  ren- 
dering the  column  of  liquid  in  the  other  leg  more  or  less 
vertical,  or  slightly  urging  the  gas  forward  by  the  mouth. 
When  sufficient  gas  has  been  transferred,  the  stopper  or  cork 
is  to  be  replaced,  and  the  circumstances  are  then  nearly  as 
they  were  at  first. 

958.  Tubes  thus  intended  for  the  production  of  gas  over 
the  acid  from  which  it  is  evolved,  are  often  advantageously 
bent  into  a  form,  which  may  be  described,  by  assuming  them 
to  have  been  coiled  obliquely  in  the  manner  of  a  long-thread- 
ed screw,  about  a  triangular  prism,  of  which  the  planes  are 

*  Edinburgh  Philosophical  Journal,  x.  251. 


IMITATION  OF   WOULFE's  APPARATUS.  439 

one  inch  wide,  so  that  each  strait  portion  of  tube  is  an  inch  and 
a  half  or  two  inches  long.  It  will  be  found,  if  sufficient  acid 
be  introduced  to  fill  one  and  a  half  of  the  straight  portions 
of  the  tube,  and  the  substance  to  be  acted  upon,  as  oxalic 
acid,  be  introduced  with  it  and  heated,  that  by  inclining 
the  tube  in  different  directions,  relative  to  a  horizontal  axis 
supposed  to  pass  through  the  prism  about  which  it  was 
moulded,  the  whole  tube,  with  the  exception  of  the  last 
divisions  at  the  open  end,  may  be  filled  with  gas.  It  is  confi- 
ned safely  during  the  revolution  by  the  quantity  of  acid  within, 
which,  as  the  gas  increases  in  volume,  travels  before  it  from 
one  end  of  the  tube  to  the  other.  When  full  of  gas,  the 
acid  may  be  replaced  by  water  (956),  and  the  gas  conve- 
niently examined  in  successive  portions,  in  a  manner  similar 
to  that  already  particularized  (950).  It  would  be  tedious  to 
explain  minutely  all  the  motions  and  positions  required  in 
working  with  these  useful  tubes;  these,  as  well  as  their  form, 
will  easily  be  understood,  by  bending  a  piece  of  wire  as  de- 
scribed (933).  The  facility  with  which  the  gas  may  be  man- 
aged in  them  may  be  easily  acquired,  by  putting  some  water 
and  a  little  air  into  such  tubes,  and  observing  their  relative 
positions  and  changes  of  place  whilst  the  tubes  are  in  motion. 

959.  A  minute  apparatus,  resembling  Woulfe's  (475,  844) 
in  its  powers  and  uses,  is  easily  formed  of  a  piece  of  tube, 

°ne  third  or  one  half  of  an  inch  in 
width,  bent  as  in  the  figure.     The 
^^^^  gas  should  be  passed  in  at  a,  and 

will  bubble  up  through  the  water  at  c  and  d,  and  if  soluble 
will  form  solutions.  If  it  be  required  that  the  gas  should 
come  into  contact  with  a  large  surface  of  water,  one  of  the 
lower  bends  should  be  extended  in  a  horizontal  position,  as  at 
d.  If  the  tube  be  bent  as  in  the  second  figure,  then  the 
portions  of  fluid  in  the  four  lower 
anSles  may  be  removed  in  succes- 
sionj  beginning  either  with  the 
strongest  or  weakest ;  or,  for  comparison,  they  may  be  re- 
moved alternately  from  either  extremity  ;  all  that  is  neces- 
sary being  the  careful  elevation  of  one  or  other  end  of  the 
tube  (931,933). 

960.  The  extremities  or  apertures  of  tubes  are  frequently 


440  GASES  LIQUEFIED  IN  TUBES. 

to  be  closed  for  a  short  time  during  operations ;  thus,  after 
a  substance  has  been  placed  in  an  open  tube,  it  may  be  de- 
sirable to  close  one  or  both  ends,  to  prevent  the  establish- 
ment of  a  current  of  air  through  it  when  heated,  or  the  dis- 
persion and  loss  of  volatile  but  condensable  substances. 
The  opening  may  be  closed  in  the  temporary  manner  re- 
quired, either  by  the  finger,  or  a  cork,  or  a  piece  of  cement, 
according  to  circumstances,  and  may  be  opened  with  equal 
facility  when  necessary. 

961.  The  readiness  and  the  ease  with  which  gases  are 
passed  over  substances  in  tubes,  either  at  high  or  low  tem- 
peratures, have  been  already  fully  pointed  out  (709,  &c.) ; 
those  practices  indeed  form  an  important  part  of  tube  chem- 
istry.    Detached  instructions  and  instances  of  this  kind  may 
be  referred  to  by  means  of  the  Index. 

962.  It  was  by  an  apparatus  constructed  entirely  from 
tubes,  that  chlorine  and  many  other  of  the  gases  were  first 
distinctly  condensed ;  and  the  results  sufficiently  indicate 
the  value  of  such  arrangements.     It  will  be  advantageous 
briefly  to  describe  the  method  of  condensing  one  of  the 
gases  which  are  most  easily  rendered  fluid,  as  cyanogen, 
and  point  out  the  attentions  necessary  in  making  the  same 
experiment  with  those  which,  requiring  higher  pressures  for 
the  purpose,  involve  the  risk  of  greater  danger. 

963.  The  tubes  chosen  should  be  of  such  thickness  as  is 
sufficient  to  resist  thrice  the  pressure  that  is  expected  to  be 
exerted  (874).     A  piece  of  about  eight  inches  long  is  to  be 
selected,  and  its  extremity  sealed  (1165,  1175);  then,  being 
softened  in  the  lamp,  at  about  five  inches  from  the  closed 
end,  it  is  to  be  bent,  not  sharply,  but  obtusely  and  roundly, 
until  the  two  limbs  make  an  angle  of  about  130°  or  140° 
(1154).     Some  cyanuret  of  mercury  is  to  be  pulverized  and 
dried  in  an  evaporating  basin,  on  the  sand-bath,  or  over  a  lamp 
at  a  temperature  which,  though  above  that  of  boiling  water,  is 
insufficient  to  decompose  the  salt,  or  at  least  to  cause  much 
change ;  it  is  to  be  rendered  quite  dry  (602),  may  be  allowed 
to  become  a  little  brown,   and  is   then  to  be  introduced 
into  the  tube  until  it  fills  three-fourths  of  the  closed  limb. 
The  open  limb  is  afterwards  to  be  wiped  clean,  if  there  be 
occasion,  with  a  wire  and  tow,  and  then  to  be  heated  and 


CASKS  LIQUEFIED CYANOGEN.  441 

drawn  off  (929,  1176),  so  as  to  leave  the  tube  with  only  a 
minute  aperture. 

964.  The  apparatus  is  now  to  be  filled  with  an  atmosphere 
of  cyanogen,  and  then  sealed  hermetically;  the  part  contain- 
ing the  cyanuret  is  therefore  to  be  heated  in  the  flame  of  a 
spirit-lamp,  until  enough  of  cyanogen  has  been  evolved  to 
expel  all  the  atmospheric  air.     This  may  be  ascertained  by 
bringing  the  aperture  towards  a  flame,  when,  if  the  small  jet 
of  gas  which  issues  is  found  to  be  combustible,  it  indicates 
that  the  tube  is  filled  with  cyanogen.     Cease  to  decompose 
any  more  cyanuret,  and  by  introducing  the  contracted  ex- 
tremity of  the  tube  into  the  lamp,  seal  it  hermetically  (1190). 
This  is  the  more  easily  done  in  consequence  of  the  gradual 
diminution  of  temperature  in  the  tube,  which  causes  the  cy- 
anogen within  to  contract  in  bulk,  and  allows  the  soft  glass 
to  coalesce  and  thicken.     Then  permit  the  whole  to  cool 
before  proceeding  to  the  evolution  and  condensation  of  the 
cyanogen. 

965.  The  tube  is  next  to  be  supported  on  a  retort  stand, 
or  on  pieces  of  wire,  in  a  position  proper  for  distillation,  that 
is  with  the  vertex  uppermost,  and  the  two  extremities  nearly 
in  the  same  horizontal  line.     A  piece  of  wet  bibulous  paper 
is  to  be  wrapped   round  the  short  and  empty  limb,  which  is 
to  retain  the  condensed  cyanogen,  and  the  flame  of  a  spirit- 
lamp  carefully  applied  to  that  containing  the  cyanuret,  so 
as  to  decompose  the  compound:  the  progress  of  the  opera- 
tion may  be  judged  of  by  the  discoloration,  fusion,  and  ulti- 
mate solidification  of  the  cyanuret.     This  process  must  not 
be  carried  on  rapidly,  or  the  heat  allowed  at  any  time  to 
rise  so  high  as  to  sublime  much  mercury :  the  appearance  of 
globules  of  sublimed  mercury  to  any  extent  in  the  upper 
part  of  the  long  limb,  is  a  proof  that  the  heat  has  been  higher 
than  was  necessary  or  proper.     The  heat  should  never  be  al- 
lowed to  rise  considerably  in  the  part  of  the  long  leg  above 
the  place  of  the  cyanuret;  and  if  the  condensation  of  cyan- 
ogen in  the  shorter  limb  is  so  rapid  as  to  make  the  moistened 
paper  sensibly  warm,  or  the  water  from  it  visibly  evaporate, 
the  operation  must  be  retarded.     The  progress  of  the  con- 
densation should  be  observed  by  slipping  the  moistened  pa- 

3F 


44*2  GASES  CONDENSED — CHOICE  OF  TUBES. 

per  off  the  end  of  the  tube  occasionally,  restoring  it  immedi- 
ately after  the  information  has  been  obtained. 

966.  In  this  way  cyanogen  may  be  condensed  without 
the  slightest  risk  of  explosion,  the  pressure  within  never  ri- 
sing above  five  or  six  atmospheres,  and  when  all  is  cold,  be- 
ing not  more  than  four  atmospheres.    Half  an  inch  or  more  in 
depth  of  the  liquid  will  be  obtained  in  the  shorter  end  of  the 
tube.     When  left  for  some  days  the  fluid  generally  returns 
to  the  black  mass  remaining  in  the  place  of  the  cyanuret, 
the  substance  having  apparently  an  attraction  for  it  resem- 
bling that  possessed  by  hygrometric  bodies  for  water.     But 
upon  repeating  the  distillation  as  just  described,  a  very  mod- 
erate heat  is  sufficient  to  separate  the  cyanogen,  and  to  ex- 
hibit it  in  a  pure  and  isolated  form. 

967.  Such  is  an  instance  of  the  condensation  of  a  gas  in 
tubes,  which  any  one  may  repeat.     It  will  easily  be  under- 
stood that,  in  the  condensation  of  gases  requiring  higher 
pressures,  the  risk  of  explosion  from  the  bursting  of  the  ves- 
sels is  comparatively  greater.     To  diminish  the  danger  as 
much  as  possible,  certain  general  precautions  should  be  at- 
tended to.     The  tubes  chosen  should  be  sufficiently  strong, 
and  be  estimated  according  to  the  directions  before  given 
(874).     They  should  be  regular  and  uniform,  and  free  from 
the  specks  or  minute  cracks  to  which  thick  tubes  are  fre- 
quently liable.     Upon  sealing  the  ends  and  bending  the  an- 
gle, the  parts  heated  should  be  exceedingly  well  annealed  ; 
for  which  purpose  the  glass  should  be  withdrawn  gradually 
from  the  flame,  and  not  allowed  to  cool  suddenly,  otherwise 
the  tubes  will  have  a  tendency  to  crack  or  fly  at  these  unan- 
nealed  places,  even  without  pressure,  and  are  then  unsafe 
for  the  experiments.     For  this  reason  the  tubes  when  sealed 
at  one  end  and  bent,  should  be  laid  aside  for  a  week  or  two, 
and  afterwards  examined  in  all  positions  with  regard  to  light; 
if  any  cracks  or  fissures  appear,  however  minute,  the  tube 
should  be  rejected.     The  bend  should  be  gradual  and  not 
sudden,  that  great  flattening  or  distortion  there  may  not  in- 
jure the  general  form  of  the  tube ;  when  bent  irregularly 
and  left  in  a  wrinkled  state,  there  is  usually  an  irregular  ten- 
sion of  the  different  parts  when  cold,  which  renders  the  glass 
exceedingly  apt  to  crack.     On  sealing  the  end  of  the  tube 


LIQUEFACTION  OF  CASES CAUTION.  443 

at  first,  it  should  be  observed  that  it  be  left  of  a  thickness 
equal  to  that  of  any  other  part,  that  it  may  have  sufficient 
strength.  On  drawing  out  the  other  extremity  also  for  the 
purpose  of  finally  closing  the  tube,  the  conical  part,  and  the 
capillary  tube  which  terminates  it,  should  be  allowed  to 
thicken  a  little  in  the  flame,  that  it  also  may  have  sufficient 
strength.  It  will  easily  be  understood,  that  the  tube  being 
of  smaller  diameter  in  that  part  than  elsewhere,  does  not  re- 
quire the  thickness  of  the  other  parts ;  but  if  it  be  drawn 
out  without  attention  to  this  point,  it  may  be  rendered  so 
thin  as  to  give  way  to  the  force  afterwards  exerted  (1172). 
It  should  also  be  observed  in  closing  the  aperture,  that  the 
extremity  be  compact  and  firm,  and  not  blown  out  or  left  in 
a  thin  film.  All  the  directions  necessary  for  effecting  these 
objects  relative  to  the  sealing  and  bending  the  glass  se- 
curely, will  be  given  in  Section  XIX,  (1179,  1183,  &c.). 

968.  The  operation  of  condensation  should  always  be  con- 
ducted slowly.     The  condensing  end  of  the  tube  should  be 
well  cooled  (927,  454) ;  in  experiments  where  gases  diffi- 
cult of  condensation  are  operated  upon,  it  is  of  essential 
importance  that  the  heated  and  the  cooled  parts  of  the  tube 
should  not  approximate  closely,  but  that  portions  of  inter- 
mediate temperatures  should  intervene,  so  that  the  tempera- 
ture shall  change  gradually  and  not  suddenly  from  one  end 
to  the  other. 

969.  A  tube  containing  the  result  of  an  operation  may 
generally  be  preserved  for  years,  without  any  further  change 
or  injury  than  what  may  be  rectified  by  cooling  the  receiv- 
ing end,  or  moderately  warming  the  other  extremity.     But 
one  or  two  instances  have  occurred,  w  ere  tubes  have  burst 
some  months  after  an  experiment  has  been  made  in  them. 
They  should  always  be  handled  with  great  caution.     Any 
sudden  contact  with  a  hard  substance,  in  the  manner  of  a 
tap  or  blow,  should  be  avoided  with  the  utmost  care;  and  if 
from  the  exertion  of  the  internal  pressure  or  other  causes  a 
crack  should  gradually  appear  in  any  part  of  the  tube,  such 
tube  should  never  be  examined,  except  with  every  precau- 
tion, even  though  it  may  seem  to  be  secure,  and  have  re- 
tained the  gas  for  months  or  years  as  well  as  at  first. 


444  LIQUEFACTION  OF  SULPHUROUS  ACID. 

970.  After  the  addition  of  some  further  brief  instructions, 
this  part  of  tube  manipulation  may  be  dismissed.     Cyanogen 
and  ammonia  may   be  evolved  and  condensed  in  dry  tubes. 
So  also  may  sulphurous  acid;  or  at  least  the  part  in  which 
the  gas  is  condensed,  may  be  retained  dry,  but  the  arrange- 
ment is  different  to  that  for  cyanogen  and  similar  gases. 
When  thestraight  pieceof  tube  selected  is  sealed  atoneextre- 
mity  as  described  (962),  mercury  is  to  be  put  into  it  for 
about  the  depth  of  an  inch,  and  over  that  the  most  concen- 
trated sulphuric  acid  is  to  be  introduced  through  a  small  tube 
funnel  to  the  depth  of  about  three  inches,  so  as  not  to  soil  the 
upper  part  of  the  vessel  (924).     An  inch  and  a  half  or  two 
inches  above  this  the  tube  is  to  be  bent  as  before  described 
(962),  and  two  or  three  inches  farther  on  is  to  be  contracted. 
Then  holding  the  tube  as  vertical  as  may  be,  the  mercury  is 
to  be  heated  very  carefully  in  the  sulphuric  acid,  until  suffi- 
cientsulphurous  acid  gas  has  been  evolved  to  eject  the  common 
air  of  the  apparatus;  this  will  be  ascertained  by  the  well- 
known  smell  of  the  acid,  or  by  the  fumes  which  it  will  yield 
when  the  aperture  is  brought  near  to  paper  moistened  with 
ammonia.     The  operator  must  then  cease  to  evolve  more  gas, 
and  having  allowed  the  temperature  of  the  tube  to  fall,  until 
scarcely  any  gas  passes  out  at  the  aperture,  the  capillary  extre- 
mity of  the  tube  should  be  introduced  into  the  flame  of  a  lamp 
fora  moment,  that  it  may  fuse  and  become  sealed  (1190); 
but  it  should  instantly  be  withdrawn,  that  it  may  cool  without 
being  expanded  by  the  gas,  which  is  still  slowly  evolved 
within.    The  tube  and  its  contents  are  then  to  be  cooled  by  a 
little  water,  or  ultimately  even  by  ice  and  water,  which  will 
cause  such  condensation  of  the  gas  within  as  to  make  the 
internal  pressure  less  than  the  external;  and  this  being  the 
case,  if  the  sealed  termination   be  not  sufficiently  strong,  it 
maybe  again  introduced  into  the  flame,  the  glass  softened  and 
allowed  to  coalesce  into  a  thicker  mass.     The  distillation  and 
condensation  of  the  gas  may  then  be  proceeded  with,  accord- 
ing to  the  directions  already  given  (965). 

971.  Many  of  the  gases,  such  as  muriatic  acid,  carbonic 
acid,  sulphuretted  hydrogen,  &c.,  are  evolved  from  materials 
which,  liberating  gas  the  moment  they  come  into  contact, 


LIQUEFACTION  OF  HYDROCHLORIC  ACID  (3AS.  445 

must  not  be  brought  together  in  the  tube  of  condensation 
before  the  second  extremity  is  securely  sealed  up;  as  that  can 
only  be  done  whilst  the  gas  or  air  has  no  tendency  to  pass 
out  of  the  tube.  The  procedure  necessary  in  such  cases  may 
be  briefly  illustrated  in  the  instance  of  muriatic  acid:  the  tube 
is  to  be  closed  and  bent  as  already  described  (962),  except 
that  the  curve  is  to  be  near  the  closed  end,  so  that  the  shorter 
leg  may  be  the  closed  one.  The  latter  is  then  to  be  filled 
by  means  of  a  tube  funnel  with  sulphuric  acid,  to  within  the 
half  or  the  third  of  an  inch  of  the  bend,  especial  care  being 
taken  that  none  of  the  acid  touch  the  inner  surface  of  the 
longer  leg:  a  piece  of  thin  platinum  foil  is  to  be  crumpled  up 
loosely,  and  thrust  up  the  long  limb  until  near  the  bend,  and 
afterwards  long  angular  fragments  of  muriate  of  ammonia, 
cut  with  the  grain  from  a  lump  (319),  are  to  be  put  up  the 
tube  by  a  wire,  until  it  is  full  to  within  an  inch  of  the  open 
end:  these  are  prevented  from  passing  into  the  sulphuric  acid 
by  the  interposed  piece  of  platinum  foil,  and  are  required  of 
an  angular  form,  that  the  acid  may  easily  flow  afterwards 
between  them  and  the  glass.  Being  so  far  arranged,  the  open 
end  of  the  tube  is  to  be  sealed  hermetically;  during  which 
operation  the  apparatus  must  be  held  in  a  position  nearly 
horizontal,  that  no  contact  of  the  sulphuric  acid  with  the 
muriate  of  ammonia  may  take  place  (1188).  That  being 
done,  the  tube  must  be  allowed  to  cool,  and  then  placed  in  a 
corner  with  the  acid  end  upwards;  the  acid  will  immediately 
flow  past  the  platinum  foil,  and  upon  the  salt  beneath,  rapid 
action  will  take  place  and  much  gas  appear  to  be  evolved. 
The  action  will  gradually  seem  to  diminish  almost  entirely, 
because  the  pressure  within  increasing  continually  for  some 
time,  the  bubbles  will  thereby  be  reduced  into  a  smaller  bulk. 
The  tube  should  be  left  in  this  position  for  some  days,  oreven 
a  week,  at  the  end  of  which  time  a  very  limpid  fluid  will  be 
perceived  here  and  there,  occupying  cavities  in  the  dense 
acid  sulphate  of  ammonia.  The  tube  being  placed  in  a 
distilling  position,  and  the  shorter  leg  cooled  (447,  924,  934), 
the  limpid  fluid  will  pass  over  into  it,  and  its  characters  may 
then  be  observed.  The  pressure  will  be  about  forty  atmo- 
spheres at  a  temperature  of  50°.  A  tube  of  half  an  inch 


446        USE  OF  TUBES  TO  PRESERVE  SUBSTANCES. 

internal  diameter,  and  ten  inches  long,  will,  in  such  an  expe- 
riment, resist  and  support  a  pressure  upon  its  internal  surface 
of  above  6000  Ibs. 

972.  In  all  cases  where  the  condensation  of  a  highly  elastic 
gas  is  to  be  effected,  the  tube  should  be  filled  as  nearly  as 
possible  with  the  materials,  that  the  space  for  aeriform  mat- 
ter may  be  the  less  ;  or  else  it  may  happen  that  the  quantity 
of  gas  evolved  from  the  substances  is  not  enough  to  do  more 
than  fill  that  space  with  an  atmosphere,  equal  to  or  less  in 
density  than  that  required  before  fluid  will  be  deposited. 


973.  One  constantly  valuable  use  of  tubes  is  for  the  reten- 
tion and  preservation  of  different  substances,  for  which  pur- 
pose they  may  often  be  used  instead  of  phials  and  bottles,  and 
are  not  unfrequently  superior  to  them.     The  tubes  in  the 
drawer  already  spoken  of  (910)  will  in  these  cases  be  had 
recourse   to,   but  they  are  improved  and  strengthened,  by 
softening  and  turning  the  edge  of  the  aperture  outwards,  so 
as  to  make  it  like  a  phial  mouth ;  they  then  allow  the  corks 
which  is  to  be  used  for  closing  them,  to  be  applied  with  more 
force.     When  deliquescent  substances,  or  such  as  would  be 
injured   by  access  of  air,  are  to  be  preserved  in  them,  the 
cork  should,  either  before  or  after  its  insertion,  be  covered 
with  wax,  or,  which  is  better,  because  it  is  not  liable  to  crack 
and  separate,  soft  cement  (1125).     The  arrangement  and 
economical  use  of  tubes  intended  to  receive  and  contain 
small  quantities   of  valuable  fluids  have  already  been  de- 
scribed (929). 

974.  A  tube,  different  in  its  kind  from  either  of  these,  is 
exceedingly  useful  for  the  preservation  of  such  portions  of 
valuable  fluids  or  solids  as,  being  intended  for  specimens, 
may  be  left  undisturbed  for  long  periods  of  time,  and  conse- 
quently may  be  sealed  up  hermetically.     The  tubes  selected 
for  this  purpose  should  be   rather  thicker  than  usual,  that 
they  may  bear  packing  when  required,  or  be  laid  with  other 
things  without  injury.     They  should  be  perfectly  clean  pre- 
vious to  the  introduction  of  the  substance,  and  when  sealed 
up  at  the  end  last  closed,  the  termination  should  be  made 
thick  and  strong  in  the  manner  described  in  Section  XIX. 


WRITING  ON  GLASS  TUBES PAPER  TUBES.  447 

(1184,  &c.)  The  substance  thus  permanently  secured  may 
be  preserved  for  years  without  change  or  injury,  and  can 
always  be  readily  examined  as  to  its  appearance  and  external 
characters.  Its  name,  with  the  date  and  other  necessary 
circumstances,  should  be  written  upon  the  exterior  of  the 
tube  with  a  scratching  diamond  (128). 

975.  Writing   in  this  manner  with  the  diamond  is  best 
done  by  laying  a  book   or  board  of  equal  thickness  with 
the  tube  upon  the  table,  and  holding  the  latter  in  the  angle 
formed  by  the  two,  by  which  steadiness  is  given  to  it :  the 
diamond  should  beheld  in  a  vertical  position  during  the  writ- 
ing, and  the  hand  retaining  it  should  be  rested  on  the  book. 
Upon  trying  to  write  on  a  piece  of  flat  glass  with  a  scratch- 
ing diamond,  turning  the  latter  round  slightly  at  the  same 
time,  it  will  be  found  that  one  position  of  it  is  more  advan- 
tageous than  any  other,  the  writing  being  then  performed 
with  greater  facility  :  this  being  ascertained,  a  notch  or  mark 
should  be  made  on  the  handle  of  the  diamond,  so  that  at  any 
future  time  this   favourable  position  may  be  immediately 
given  to  it. 

976.  When  tubes  are  required  for  the  conduction  of  gas 
or  vapour,  it  has  been  already  shown  that  in  cases  of  emer- 
gency such  as  are  made  of  paper  (247,  272,  841)  may  be 
substituted  for  those  of  glass  or  metal.     It  is  often  advanta- 
geous to  render  the  paper  difficult  of  combustion,  that  the 
accidental,  and  at  times  even  necessary,  approach  of  flame 
may  not  occasion  injury.     This  may  be  done  by  washing  the 
paper  with  a  strong  solution  of  alum,  or  phosphate  of  soda, 
common  salt,  or  better  still  with  alkali  or  carbonated  alkali, 
provided  these  do  not  interfere  afterwards  with  the  uses  of 
the  tube,  or  paper,  or  the  substances  which  are  to  be  passed 
through  them  (1337). 

977.  Such  are  some  of  the  numerous  applications  of  tubes 
for  the  performance  of  chemical  experiments.     Many  varia- 
tions of  the   forms  mentioned   will   suggest  themselves  in 
practice  as  affording  facilities  in  particular  cases.     It  would 
have  occupied  far  too  much  room  to  have  enumerated  all 
that  have  been  found   useful ;  and  indeed  throughout  this 
chapter,  general  forms  have  been  referred  to  and  described, 


448  ELECTRICITY, 

rather  than  particular  ones ;  for  their  uses  and  properties 
once  known,  the  variations  will  easily  be  understood.  The 
economy  and  exceeding  facility  afforded  by  this  kind  of 
apparatus  in  situations  distant  from  the  usual  sources  of 
more  perfect  instruments,  and  its  superiority  in  some  cases 
over  any  other  that  has  yet  been  devised,  are  sufficient  to 
recommend  it  to  full  and  general  attention  :  and  when  com- 
bined with  the  use  of  a  few  fragments  of  glass  and  paper 
vessels,  as  is  hereafter  to  be  described  (1335),  placed  in  the 
hands  of  every  one,  whatever  his  situation  may  be,  opportu- 
nities of  pursuing  chemical  researches  to  a  very  considerable 
extent. 


SECTION  XVII. 
ELECTRICITY. 

978.  IN  consequence  of  the  very  general  and  close  asso- 
ciation of  chemistry  with  all  the  other  sciences,  the  chemist  is 
often  obliged  to  work  with  instruments,  and  to  make  arrange- 
ments which,  although   they  seem  essentially  to  belong  to 
other  pursuits,  are  at  times  highly  influential  over  his  own. 
The  powers  of  Electricity,  amongst  others,  are  so  closely 
allied  to  those  of  Chemistry,  and  possess  such  vast  influence 
in  aiding  or  opposing  them,  that  the  experimenter  in  this 
science  is  continually  resorting  to  them  in  his  peculiar  and 
every  varying  examinations  of  matter.     For  this  reason  so 
much  of  the  management  of  electrical  machines  and  appa- 
ratus as  is  frequently  required  in  the  laboratory  will  be  de- 
scribed in  this  section,  and  the  circumstances  necessary  to 
facilitate  investigation,  or  secure  success,  will  be  particularly 
pointed  out. 

§  1.  Ordinary  Electricity. 

979.  The  common  electrical  machine  is  of  constant  use 


ELECTRICAL  MACHINE EXCITED.  449 

for  the  passing  of  sparks  or  currents  of  electricity  through 
gases,  for  charging  a  jar,  or  for  conferring  particular  states 
of  electrical  tension  upon  insulated  bodies.  When  required 
for  use  it  generally  wants  some  degree  of  preparation  to 
bring  it  into  strong  action.  In  favourable  weather,  merely 
wiping  the  machine  with  a  warm  linen  cloth,  and  afterwards 
with  a  silk  handkerchief,  is  sufficient  for  the  purpose  ;  but 
usually,  and  especially  in  damp  weather,  it  will  require 
warming.  This  may  be  done  occasionally  by  placing  it  be- 
fore a  fire  and  turning  the  handle  at  intervals,  that  all  parts 
may  be  exposed  to  the  heat;  but  it  is  more  advantageous,  as 
well  as  safer,  to  attain  the  same  end  by  placing  the  machine 
in  a  current  of  hot  air;  or  if  it  be  required  for  continued  use 
in  one  particular  place,  to  pass  a  stream  of  hot  air  against 
and  about  it.  A  machine  may  be  very  effectually  warmed 
by  placing  it  over  a  sand-bath  or  hot  iron  plate  of  a  tem- 
perature not  more  than  212°,  by  which  not  only  does  the 
plate  or  cylinder,  but  also  the  glass  insulations  become 
thoroughly  warm.  At  other  times  a  current  of  air  heated  by 
a  crucible  furnace  (269)  may  be  conveniently  conveyed  to 
the  machine,  the  warm  air  being  occasionally  conducted  by 
paper  pipes  (1337).  Another  expedient,  and  a  very  good 
one  with  cylinder  machines,  is  to  place  a  chemical  lamp  (2 12) 
with  a  low  flame  beneath  the  cylinder,  and  to  support  a  plate 
of  metal  about  six  inches  square  nearly  an  inch  above  the 
chimney  of  the  lamp  (270).  This  plate  prevents  the  ascent 
of  the  comparatively  small  hot  current  of  air  from  the  lamp 
(which  would  heat  the  cylinder  in  spots  only,  and  those  far 
too  highly),  it  becomes  itself  hot,  warms  the  air  lying  upon  it, 
and  thus  produces  a  large  current  moderately  heated,  which 
surrounds  the  cylinder  on  all  sides,  and  thoroughly  warms  it. 
980.  During  the  warming  of  a  machine,  care  should  be 
taken  to  give  it  as  equable  a  temperature  as  possible,  and  it 
should  be  continually  watched  that  no  part  become  so  hot 
as  to  melt  the  cement  used  in  its  construction.  The  warmth 
of  the  insulating  parts  should  be  particularly  attended  to ; 
for  in  damp  weather  a  machine  which  will  appear  to  be  in  ex- 
cellent action  and  give  out  long  electrical  brushes  from  its 
cylinder  or  plate,  will  often  scarcely  give  a  spark  from  the 


450  ELECTRICAL  MACHINE WARMED. 

conductor,  because  of  the  dampness  of  the  insulating  glass 
pillar. 

981.  Whilst  a  machine  is  being  warmed    it    should  be 
wiped  with  a  dry  cloth  or  a  silk  handkerchief;  the  rubbers 
should  be  examined,  all  dust  taken  from  them,  and  amalgam 
applied  if  required:  this  may  be  known  by  observing  whether 
the  amalgam  has  broken  away,  or  has,  by  age  and  disuse, 
concreted  into  a  hard  brittle  mass  that  will  not  adapt  itself, 
or  present  a  good  surface,  to  the  passing  glass.     If  the  cylin- 
der have  many  spots  of  amalgam  upon  it,  and  several  of  them 
large,  they  should  be  removed:  they  may  easily  be  scraped 
off  by  the  thumb-nail  or  a  piece  of  wood.     A  few  small  spots 
appear  rather  to  increase  than  diminish  the  activity  of  the 
machine,  and  the  silk  which  proceeds  from  the  rubber  to  a 
certain  distance  over  the  glass,  is  far  better  when  from  use  it 
has  become  impregnated  with  amalgam,  than  when  it  is  quite 
clean  and  free  from  that  substance.     It  is  often  advantageous, 
especially  when  the  machine  is  required  in  haste,  to  hold  a 
piece  of  silk  with  some  amalgam  upon  it  against  the  plate  or 
cylinder,  whilst  it  is  turned,  and  also  to  rub  up  the  surface  of 
the  amalgam  upon  the  rubber  with  the  same  amalgamated  silk. 
To  apply  the  amalgam  to  the  silk,  it  is  necessary  first  to  put  a 
little  tallow  upon  the  latter,  after  which  the  amalgam  will 
adhere.     The  amalgam  itself  should  be  rubbed  in  a  mortar 
with  a  little  tallow,  before  it  be  considered  fit  for  any  use 
about  the  machine.    The  rubbers  should  press  lightly  against 
the  glass.     The  silk  proceeding  from  them  over  the  cylinder  is 
better  unoiled  than  oiled. 

982.  When  the  machine  is  in  good  order,  the  prime  con- 
ductor away,  and  the  handle  turned,  it  should  send  out  an 
uninterrupted  series  of  brushes  from  the  edge  of  the  silk,  with 
continual  sparks  fly  ing  round  the  glass.    The  appearance  pre- 
sented by  bringing  the  knuckles  near  the  edge  of  the  silk,  is  a 
very  good  indication  of  the  exciting  power  of  the  machine. 
These  effects  should  take  place  without  causing  considerable 
friction  between  the  glass  and  the  rubber  and  silk,  or,  if  there 
be  much,  it  should  be  from  adhesion  between  the  glass  and  the 
silk,  and  not  from  the  pressure  of  the  rubber.     In  that  case  it 
is  easily  diminished,  and  the  labour  of  turning  lessened  by 


PLATE-MACHINES ARRESTING  A  CRACK.  451 

folding  back  the  silk  more  or  less,  so  as  to  lessen  the  part  in 
contact  with  the  glass. 

983.  Upon  putting  the  prime  conductor  into  its  place,  and 
continuing  the  motion,  sparks  two  or  three  inches  in  length, 
should  fly  rapidly  from  it  to  the  knuckle,  or  to  a  clean  brass 
ball  held  near  it.     For  these  trials  of  the  length  of  spark, 
and  for  discharges,  where  the  passage  of  a  spark  is  necessary 
in  other  circumstances,  a  metal  ball  is  better  than  the  knuckle 
or  back  of  the  hand;  the  hairs,  moisture,  and  adhering  fila- 
ments of  the  latter,  frequently  diminish  the  effect. 

984.  The  machine,  when  out  of  use,  should  be  set  aside  in 
a  dry  room  or  cupboard,  away  from  the  fumes  of  the  labo- 
ratory (29),  and  it  is  advantageous  to  throw  a  coarse  linen 
bag  over  it  as  a  cover  to  keep  off  dirt,  and,  to  a  certain 
extent,  moisture  and  fumes. 

985.  The  manner  in  which  plate  machines  are  mounted, 
namely,  by  an  axis  passing  through  the  middle  of  the  plate, 
made  tight  by  collars  or  screws,  generally  causes  an  irregula- 
rity of  tension,  by  which  a  tendency  to  crack  from  the  centre 
it  produced.     This  renders  the  machine  liable  to  injury  from 
circumstances  otherwise  unimportant;  and  warming  it  too 
much  at  the  middle  before  a  fire,  or  partially  only,  or  slight 
mechanical  strains,  cause  cracks  to  originate  there  which, 
though  small  at  first,  gradually  extend  till  they  reach  the  cir- 
cumference, unless'means  be  adopted  to  stop  their  progress. 
This  is  best  done  by  directing  an  instrument-maker  to  drill  a 
small  hole  through  the  glass,  a  little  in  advance  of  the  crack, 
and  in  its  course.     When  the  crack  reaches  the  hole  it  gene- 
rally stops,  and  the  plate  is  saved  for  a  time  till  other  cracks 
are  formed,  which  gradually  weaken,  and  finally  destroy  the 
machine. 

986.  The  machine  is  used  to  give  sparks  directly  from  its 
conductor:  these,  when  passed  through  eudiometers,  either 
inflame  the  mixture  of  gases  within,  or  occasioning  chemical 
changes  of  a  slower  kind,  require  to  be  repeated  a  great 
number  of  times.     A  spark  of  sufficient  intensity  to  inflame 
a  combustible  gaseous  mixture,  may  often  be  taken  from  a 
machine  to  one  of  the  wires  of  an  ordinary  eudiometer,  the 
other  wire  being  in  contact  with  the  finger  or  connected  with 
the  earth  throughconducting  matter.   But  it  will  occasionally 


452  THE  SPARK SMALL  HOLES — IGNITED  BODIES. 

be  found  exceedingly  difficult  to  succeed  in  the  experiment, 
solely  from  inattention  to  some  slight  circumstance  about  the 
arrangement.  The  wires  which  are  fixed  into  a  detonating 
eudiometer  are  so  placed  as  to  have  their  inner  extremities  at 
a  small  distance  from  each  other.  These  terminations  are  not 
always  finished  off  with  sufficient  care,  the  wires  being  either 
simply  cut  by  pliers,  or,  if  filed  into  shape,  are  still  left  with 
some  projecting  corner  or  irregularity.  Sometimes  the  wires 
themselves  are  too  thin. 

987.  All  these  circumstances  tend  to  make  an  electric 
discharge  pass  rather  as  a  coarse  brush,  or  as  a  succession 
of  minute  sparks,  than  as  one  decided  luminous  flash.     This 
tendency  is  still  further  increased,  if  the  exterior  ends  of  the 
wires  are  also  small,  or  are  only  turned  into  a  little  loop ; 
and  it  will  then  be  found  almost  impossible  to  send  a  spark 
from  the  prime  conductor  in  an  undivided  state  through  the 
interior  of  the  tube.     When  defects  of  this  kind  are  found 
to  exist,  they  may  be  partially  remedied  by  putting  a  ball 
half  an  inch  or  an  inch  in  diameter  upon  the  wire,  which  is 
to  be  brought  near  the  conductor ;  this  ball  will  receive  a 
large  distinct  spark,  and  will  transmit  it  from  the  one  wire 
to  the  other  within  the  eudiometer  in  a  single  discharge, 
even  though  the  latter  were  to  terminate  almost  in  points.* 

988.  Sometimes  a  eudiometer  which  permits  a  spark  to 
pass  with  perfect  facility,  through  gas  confined  in  it  over 
mercury,  will  not  with  gas  over  water.     The  film  of  water 
with  which  the  interior  of  the  instrument  is  moistened  inter- 
feres in  this  case,  and  conducts  the  electricity  of  a  spark 

*  Although  not  expressly  connected  with  such  parts  of  the  subject  of  elec- 
tiicity  as  are  selected  by  the  author,  the  following  observations  being,  I  believe, 
new,  and  of  some  practical  interest,  I  deem  it  not  mal  apropos  to  insert  them 
here. 

1.  Small  apertures  in  non-conductors  discharge  electricity  as  points  do.     If  a 
piece  of  very  thin  sheet-caoutchouc  be  tied  over  the  knob  of  a  prime  conductor, 
the  first  spark  taken  from  the  knob  generally  ruptures  the  membrane,  and  creates 
in  it  an  imperceptible  aperture,  through  which  the  electric  fluid  constantly  is- 
sues into  the  surrounding  air,  in  a  manner  exactly  resembling  that  produced  by 
a  point. 

2.  Metals  in   a  state  of  intense  ignition,  even  though  terminating  in  large 
knobs,  cause  the  discharge  of  electricity  at  a  distance  quite  as  great  as  do  the 
sharpest  points  when  cold.    The  state  of  intense  ignition,  in  any  other  case,  pro- 
duces a  like  effect ;  thus  the  flame  of  a  lamp  or  candle,  when  uninsulated,  pre- 
vents the  excitement  of  a  prime  conductor  at  a  very  considerable  distance. — ED. 


EUDIOMETER LEYDEN  JAR.  453 

given  in  the  ordinary  manner,  to  such  an  extent  as  to  pre- 
vent its  passage  from  point  to  point  of  the  wires  within.  In 
these  cases  the  application  of  the  large  ball  on  the  outside 
(987)  will  often  remedy  the  evil,  by  enabling  a  more  power- 
ful spark  to  be  drawn  from  the  machine.  If  it  has  not  this 
effect,  the  charge1  of  a  Leyden  jar  must  be  used:  the  ball  in 
these  cases  need  not  necessarily  be  fixed  upon  the  eudiom- 
eter, it  may  be  hung  from  it  by  wire,  or  the  knob  of  a  dis- 
charging rod,  the  metal  of  which  is  held  against  the  end  of 
the  eudiometer  wire,  may  be  substituted,  or  it  may  be  arrang- 
ed in  many  other  ways.  The  necessary  points  to  be  atten- 
ded to  are,  that  the  ball  and  the  eudiometer  wire  make  an 
undivided  metallic  communication,  the  whole  of  which  is  in- 
sulated, and  that  the  spark  be  received  by  the  ball. 

989.  In  all  these  eudiometric  explosions,  the  other  wire 
of  the  tube  must  be  in  communication  through  a  finger,  or  a 
chain,  or  some  conducting  matter  with  the  ground.     The 
whole  of  these  operations  are  effected  with  admirable  facil- 
ity by  a  single  person,  with  the  detonating  eudiometer  of  Or 
Ure  (999). 

990.  A  Leyden  jar  of  the  capacity  of  a  quart  will  be  suffi- 
cient for  all  ordinary  laboratory  purposes.     The  ball  should 
be  at  least  an  inch  in  diameter,  and,  with  the  wire  and  wooden 
top,  should  be  so  firmly  fixed  to  the  jar,  that  the  latter  may 
be  placed  in  any  required  position  without  fear  of  their  fall- 
ing, or  being  deranged.     For  the  same  reason  the  connex- 
ion between  the  ball  and  the  coating  within  should  be  made 
by  wire  and  not  by  a  chain,  that  the  communication  may  be 
perfect  in  every  position.     The  jar  when  new  should  be 
warmed  and  wiped  on  the  outside,  and  then  examined  rela- 
tively to  certain  points;  and  first,  as  to  its  freedom  from  the 
fault  of  permitting  spontaneous  discharge.  The  jar  being  held 
by  its  exterior  coating,  should  have  its  knob  placed  in  contact 
with  the  machine   when   in  good  order,  and  should  be  as 
highly  charged  as  possible.     If  the  jar  does  not  discharge 
itself,  or  permit  a  spark  to  pass  over  the  external  uncoated 
glass,  it  is  in  that  respect  good  ;  if  it  discharge  sponta- 
neously, but  only  when  very  highly  charged,  it  is  moderately 
good;  if  it  discharge  spontaneously  with  readiness  and  free- 


454  LEYDEN  JAR ITS  PROPERTIES. 

dom,  even  with  comparatively  low  electrical  charges,  it  is 
bad.  This  fault  may  sometimes  be  cured  by  paring  away 
half  an  inch  or  more  of  the  exterior  coating  at  the  upper 
edge,  so  as  to  make  the  distance  between  it  and  the  wire  of 
the  ball  greater ;  or  by  removing  some  accidental  angular 
projection  or  point  on  the  wire  or  wooden  top,  which  has 
facilitated  spontaneous  discharge. 

991.  If  a  jar  prove  good  when  tried  as  above,  it  should 
then  be  examined  as  to  its  power  of  retaining  a  charge  undi- 
minished.     For  this  purpose  the  jar  should  be  highly  charg- 
ed, an$  then  immediately  discharged  by  the  discharging 
rod,  the  length,  brilliancy,  and  sound  of  the  spark   being  at 
the  same  time  observed.     It  should  then  be  charged  to  the 
same  degree  as  before,  and  being  removed  from  the  conduc- 
tor, should  be  left  a  minute  in  the  air  before  it  be  discharged, 
and  the  spark  again  observed  and  compared  with  the  former. 
It  will  readily  be  seen  whether  in  consequence  of  standing 
for  the  minute  the  spark  is  smaller,  and  also  whether  the  di- 
minution has  been  much  or  little. 

992.  There  are  no  jars  which  do  not  lose  considerably, 
even  in  a  short  interval  of  lime,  if  very  highly  charged,  but 
if  only  moderately  charged,  they  should  suffer  much  less 
dissipation  of  electricity,  and  ought  to  yield  a  spark  of  con- 
siderable  force  after  a  lapse  of  five  minutes.     A  jar  of  the 
size  above  mentioned,  when  dry  and  warm  and  well  charged, 
should,  after  a  lapse  of  ten  minutes,  give  a  spark  at  least 
half  an  inch  in  length  to  the  ball  of  the  discharging  rod,  the 
ball  being  one  third  of  an  inch  in  diameter. 

The  retention  of  the  charge  by  an  electric  jar  in  chemical 
experiments,  is  frequently  of  great  importance,  from  the 
unavoidable  delays  which  often  occur  before  the  spark  can 
be  passed. 

993.  A  jar  for  eudiometrical  experiments  is  much  more 
conveniently  discharged  by  a  wire,  than  by  the  usual  glass- 
handled   discharger.     A   piece  of  copper  wire   about  one 
twentieth  of  an  inch  in  thickness  should  be  connected  with 
the  outside   coating,  by  being  passed  round  the  body  of  the 
jar,  and  made  tight  by  twisting  it,  the  piece  left  to  act  as  a 
discharger  being  about  18  inches  in  length.     The  loose  end 


WIRE  DISCHARGER EUDIOMETER  MANAGED.  455 

should  be  coiled  up  into  a  flat  spiral  of  a  couple  of  turns, 
to  prevent  its  acting  as  a  mere  point,  or  if  a  little  metallic 
ball  or  a  very  small  bullet  be  fixed  upon  it,  the  arrangement 
will  be  more  complete.  This  wire  performs  the  part  of  a 
discharger  whenever  required,  and  being  in  constant  contact 
with  the  outside,  and  also  very  flexible,  it  may  be  adapted  to 
nearly  every  possible  occasion.  Suppose,  for  instance,  that 
the  machine  will  not  yield  a  spark  sufficiently  powerful  to 
inflame  a  mixture  of  gases  in  an  eudiometer  tube  (986),  and 
that  a  discharge  is  requisite,  the  jar  must  be  charged  and 
then  discharged  in  the  following  manner.  The  loose  end  of 
the  attached  wire  is  first  to  be  placed  and  retained  in  contact 
with  one  of  the  eudiometer  wires,  and  then  the  ball  of  the 
jar  approached  to  the  other  wire ;  the  discharge  will  imme- 
diately be  made  through  the  instrument  without  any  risk  of 
inconvenience  to  the  experimenter,  even  though  he  hold  the 
wire  and  jar  in  his  hand  during  the  operation. 

994.  There  are  certain  points  in  the  management  of  a 
eudiometer,  relative  to  the  method  of  holding  it  during  an 
explosion,  which  require  the  attention  of  the  student.     The 
common  detonating  eudiometer  is  a  short  glass  tube  closed 
at  the  upper  extremity,  and  having  two  pieces  of  platinum 
wire  passing  near  that  extremity  through  the  glass,  so  that 
their  inner  terminations  are  within  a  very  short  distance  of 
each  other.     These  wires,  being  made  parts  of  the  metallic 
communication  of  a  charged  jar  as  before  described,  conduct 
the  electricity,  and  cause  a  discharge  to  be  effected  through 
or  between  them.     The  gas  to  be  subjected  to  the  spark  is 
generally  such  a  mixture  as  will  inflame.     It  is  to  be  trans- 
ferred into  the  tube  over  water  or  mercury,  according  to 
circumstances  (762,  788),  and  the  lower  open  end  of  the  eudi- 
ometer is  necessarily  retained  in  the  water  or  mercury  during 
the  experiment  to  confine  the  gas. 

995.  When  the  gas  has  been  introduced,  the  outside  and 
upper  part  of  the  eudiometer  is  to  be  wiped  clean  and  dry, 
so  that  no  water  or  mercury  may  adhere  to  it.     The  instru- 
ment should  then  be  held  firmly  and  upright,  which  is  per- 
haps best  effected  by  grasping  it  with  the  first  three  fingers 
on  the  one  side,  whilst  the  thumb  and  little  finger  are  press- 


456  EUDIOMETER MANAGEMENT. 

ed  against  it  on  the  other.  The  hand  should  be  about  the 
middle  of  the  tube,  and  out  of  the  way  of  the  wires  above, 
that  the  knob  of  the  charged  jar  may  not  come  near  it  during 
the  experiment.  The  tube  should  be  supported  by  the  hand 
alone,  its  lower  end  not  being  allowed  to  touch  the  bottom 
of  the  vessel  in  which  it  stands  during  the  explosion,  lest  it 
strike  against  it  with  such  force  as  to  be  broken  or  injured. 
It  is  advisable,  wherever  it  can  be  done,  to  apply  a  finger  of 
the  unoccupied  hand  with  slight  force  to  the  bottom  of  the 
detonating  tube  under  the  fluid  at  the  moment  of  explo- 
sion: this  allows  the  descent  of  the  water  or  mercury  during 
the  explosion,  but  as  contraction  takes  place  it  is  drawn 
against  the  aperture,  and  prevents  the  fluid  rushing  in  at  once. 
By  withdrawing  it  gradually,  the  water  or  mercury  is  admit- 
ted in  a  more  tranquil  manner  than  would  otherwise  be  the 
case;  and  indeed  the  impetuosity  of  the  action  is  altogether 
restrained,  and  the  probabilities  of  loss  of  the  contents  of  the 
eudiometer  diminished. 

996.  As  before  mentioned  relative  to  a  spark  from  the 
conductor  (986,  &c.),  so  also  here,  if  the  wires  be  pointed,  a 
ball  may  be  advantageously  used ;  and  if  the  interior  be  so 
moist  as  to  transmit  all  the  electricity  of  a  small  or  moderate 
charge,  then  a  large  charge  must  be  passed. 

997.  The  proportion  of  gas  which  may  be  detonated  with 
safety  in  an  eudiometer  tube,  depends  considerably  upon 
the  explosive  power  of  the  particular  mixture  under  exami- 
nation, and  also  upon  the  quantity  detonated  at  once.     A 
mixture  of  oxygen  with  carbonic  oxide  expands,  when  in- 
flamed, with  much  less  force  than  a  mixture  of  oxygen  with 
hydrogen  or  olefiant  gas ;  and  a  large  quantity  will  of  course 
expand  with  more  force  than  a  smaller.     But  besides  con- 
sidering the  efficiency  of  the  eudiometer  tube  in  resisting  the 
expansive  force,  occasioned  by  detonation,  the  experimenter 
has  also  so  to  proportion  the  quantity  of  gas,  that  whilst 
expanding  there  shall  be  abundant  space  in  the  tube  to  re- 
tain the  products  under  their  greatest  volume  and  agitation, 
that  no  loss  may  occur.     No  more  gas  should  be  introduced 
into  a  tube  for  detonation  than  will  occupy  a  sixth  of  its  ca- 


457 

pacity  at  common  temperatures,  and,  generally,  it  will  be 
safer  and  advisable  to  employ  much  less. 

998.  In  operations  with  the  ordinary  eudiometer  tube,  two 
persons  are  usually  required,  one  to  hold  and  manage  the 
instrument,  the  other  to  pass  the  electric  discharge.     The 
second  person  may  however  be  dispensed  with,  by  a  little 
contrivance.     The  jar  may  be  placed  upon  the  table  with  its 
knob  in  contact  with  the  prime  conductor  of  the  machine, 
and  with  a  wire  of  two  feet  in  length,  made  fast  to  one  of  the 
eudiometer  wires,  that  sufficient  motion  may  be  allowed  in 
connexion  with  its  outside.     One  end  of  another  wire   of 
equal  length  is  to  be  attached  to  the  second  eudiometer  wire, 
and  the  other  end  made  fast  to  a  metallic  ball,  which  is  to 
be  placed  within  half  an  inch  of  any  part  of  the  prime  con- 
ductor.    The  ball  with  its  wire,  though  it  is  not  essential, 
may  be  insulated  with  advantage,  and  for  this  purpose  it 
may  be  supported  on  the  mouth  of  a  glass  or  a  bottle,  raised 
upon  a  stool  or  other  convenient  support  (20).     The  opera- 
tor may  then  hold  the  eudiometer  tube  (994)  in  one  hand, 
and  turn  the  machine  with  the  other:  when  the  charge  in 
the  jar  has  acquired  such  intensity  as  to  pass  over  the  half 
inch  of  air  between  the  conductor  and  the  ball,  the  jar  will 
be  discharged  through  the  eudiometer  wires.      The  hand 
which  holds  the  tube  should  be,  as  before  mentioned,  clear 
of  the  wires  (995) ;  and  it  is  proper  not  to  touch  the  outside 
of  the  jar  or  any  of  the  wires  during  the  experiment,  lest  from 
some  unperceived  circumstance  the   discharge  should   be 
made  through  the  body. 

999.  Dr  lire's  eudiometer  *  (989)  renders  the  experiment 
easy  of  performance  by  a  single  person.     This  instrument, 
which  consists  of  a  glass  tube  furnished  with  wires  in  the 
usual  manner,  is  bent,  so  that  the  open  extremity  is  turned 
up  nearly  as  high  as  the  closed  one.     It  is  to  be  filled  with 
water  or  mercury,  and  the  gas  transferred  into  it  in  the  or- 
dinary manner  ;  then,  being  placed  upright,  part  of  the  fluid 
in  the  open  leg  is  displaced  by  inserting  a  glass  rod,  or  in 
some  other  manner.     The  open  leg  being  grasped  by  the 

*  Edinburgh  Philosophical  Transactions,  1818. 

3  H 


458  BATTERY HENLEY'S  ELECTROMETER. 

hand,  the  thumb  is  to  be  placed  tightly  over  the  aperture, 
so  as  to  close  it,  and  at  the  same  time  to  touch  one  of  the 
wires ;  a  spark  taken  from  the  conductor  to  the  other  wire 
passes  through  the  gas,  inflaming  it,  and  is  conducted  off  by 
the  thumb  and  hand.  The  gas  in  expanding  depresses  the 
fluid  beneath  it,  whilst  the  air  in  the  part  closed  by  the  thumb 
acts  as  a  spring  to  restrain  the  violence  of  the  explosion.  If 
a  charge  from  a  jar  (993)  is  to  be  passed,  then  the  thumb 
must  not  be  allowed  to  touch  the  wire  whilst  closing  the 
aperture ;  when  the  jar  is  charged,  the  wire  connected  with 
the  outer  coating  is  first  to  be  hooked  upon  the  eudiometer 
wire  nearest  the  thumb,  and  securely  retained  there,  so  as 
not  to  slip  during  the  experiment,  and  then  the  knob  of  the 
jar  is  to  be  brought  to  the  other  wire,  and  the  gas  will  be 
inflamed. 

1000.  It  will  be  unnecessary  particularly  to  describe  the 
arrangements  of  a  battery,  which  belong  principally  to  the 
electrician.     Whenever  its  use  is  required  in  the  laboratory, 
it  should  be  ascertained  that  all  the  outside  coatings  are  well 
and  securely  connected  together  by  metallic  substances,  as 
wires  or  sheets  of  metal;  that  the  internal  coatings  are  in 
proper  connexion  with  each  other,  through  their  appropriate 
mountings  and  wires;  that  no  wire  or  thread,  or  conducting 
matter  of  any  kind,  extend  in  any  way  from  the  case  or  ex- 
ternally coated  parts  of  the  jars,  towards  the  knobs  and  wires 
connected  with  the  insides;  and  that  no  filamentous  or  pointed 
substance,  nor  any  projecting  metallic   body  remain   in  the 
neighbourhood  of  the  battery  during  the  time  it  is  in  use. 

1001.  If  a  Henley's  electrometer  be  used  to  show  the  pro- 
gress of  the  charge,  it  should  be  so  placed  that,  as  the  index 
moves,  it  shall  not  approach  to  any  ball,  or  wire,  or  surface 
charged  similarly  to  itself,  but  recede  from  it;  if  placed  upon 
the  end  of  the  conductor,  therefore,   the  index  should   be 
allowed  to  move  outwards  and  away  from  the  conductor,  and 
not  in  a  direction  over  it  towards  its  more  central  parts;  the 
latter  would  interfere  with  the  free  indication  of  the  instru- 
ment, and  sometimes  even  render  it  quite  useless.* 

*  In  the  place  of  pith-balls,  such  as   are  usually  attracted  to  the  prime  con- 
ductor, the  Editor  uses  thin  gum-elastic  bags  covered  with  gold-leaf,  which,  by 


RESIDUAL  CHARGE SUBSTITUTE  FOR  JARS.  459 

1002.  When  a   battery   is  in   use,  the  operator  should 
beware  of  discharging  it  accidentally  by  means  of  his  own 
person;  for  though  the  shock  might  do  no  bodily  harm,  it 
might  cause  involuntary  movement,  and  the  derangement 
of  an  important  experiment:  being  therefore  once  well  and  se- 
curely arranged,  the  wires  and  metallic  connexions  should 
not  be  unnecessarily  approached  after  the  charging  has  com- 
menced, until  after  the  explosion. 

1003.  When  a  battery  has  been  used,  the  experimenter 
should  beware  of  the  residual  charge.  During  the  time  occu- 
pied in  charging  a  battery,  a  diffusion  of  electricity  takes 
place  over  that  part  of  the  uncoated  glass  which  is  near  the 
edge  of  the  foil;  this  is  not  entirely  removed  on  the  discharge 
of  the  coated  part,  but  afterwards  gradually  returns  to  the 
coatings  and  recharges  the  battery,  occasionally  to  a  consi- 
derable extent:  hence  if,  after  the  discharge  of  a  battery,  it 
be  left  a  few  minutes  with  its  internal  coating  uncommuni- 
cated  with  the  earth  or  with  the  exterior  coating,  it  will  be 
found,  upon  applying  the  discharger,  to  afford  a  considera- 
ble spark. 

1004.  When  a  regular  electrical  jar  cannot  be  obtained, 
an  excellent  substitute  may  be   formed  from  a  large  thin 
medicine   phial,   by   filling   it    two-thirds   or  three-fourths 
with  metallic  filings,  coating  the  outside  to  the  same  height 
with  pasted  tin  foil,  and  closing  the  mouth  by  a  cork,  thrust  in 
nearly  to  a  level  with  the  top  of  the  neck;  a  thick  wire  is  to  be 
passed  through  the  cork  so  that  one  end  shall  enter  the  filings, 
and  the  other  project  about  three  inches  above  the  cork;  a 
bullet  or  other  convenient  metallic  ball  is  to  be  attached  to 
its  extremity.     A  ready  substitute  for  a  jar  may  also  be  made 
of  a  piece  of  thin  glass  tube  of  large  diameter,  coated  on  the 
inside  and  outside  with  tin  foil,  to  within  two  inches  of  each 
end,  and  furnished  with  a  knob  and  wire  connected  with  the 
inside  coating  as  just  described.     A  plate  of  crown  glass 
coated     on    both    sides  with   tin    foil    to  within  an     inch 
and  a  half  of  the  edges,  also  makes  a  good  substitute,  but  re- 
reason  of  their  lightness,  may  be  made  several  inches  in  diameter,  and  yet  will 
stand  erect  when  the  machine  is  excited.     When.not  gilded,  these   bags  cling 
tenaciously  to  tlie  prime  conductor.— ED. 


460  ORIGINAL  LEYDEN  JAR DISCHARGER. 

quires  care  in  the  handling,  lest  it  be  discharged  through  the 
fingers. 

•  1005.  A  still  simpler,  although  not  so  effectual  an  instru- 
ment, is  the  original  Leyden  bottle.  Fill  a  thin  Florence  flask 
two-thirds  full  of  water,  put  a  nail  or  wire  through  a  cork  in 
the  mouth,  so  that  the  metal  may  dip  into  the  water  an  inch 
or  two;  let  its  outer  end  terminate  in  a  coil  or  ball  (993). 
Wipe  the  flask  dry,  grasp  the  lower  part  in  the  palm  of  the 
hand  and  fingers,  and  then  charge  it  from  the  machine.  It 
will  now  give  a  very  considerable  discharge;  but  the  discharge 
should  be  made  immediately  after  the  charge,  and  the  whole 
arrangement  acts  better  if  it  be  warmed  beforehand.  The 
water  on  the  inside  and  the  hand  on  the  outside  are  the  coat- 
ings of  the  bottle.* 

1006.  A  very  effectual  and  cheap  discharger  is  made  of  a 
piece  of  thick  wire  about  twelve  inches  long,  curved,  termi- 
nated by  a  bullet  at  each  end,  and  supported  in  the  middle 
by  a  stick  of  sealing-wax  as  a  handle;  in  many  cases  even 
the  stick  of  sealing-wax  is  not  required  to  complete  the  dis- 
charger (993). 

1007.  The  electrophorus  is  an  instrument  which  would  not 
claim  the  attention  of  the  chemist,  but  that,  ]being  easily 
constructed  with  materials  obtainable  in  almost  every  place, 
it  may  be  rendered  effectual  in  supplying  the  want  of  an 
electrical  'machine  for  usual  laboratory  purposes.     A  sheet 
of  tin  foil  is  to  be  laid  smoothly  in  the  bottom  of  a  flat  dish, 
so  that  its  edges  may  rise  up  all  round  ;  or  it  may  be  laid 
upon  a  flat  surface,  with  its  edges  rising  up  against  the  in- 
side of  a  hoop  placed  to  confine  them.     Equal  parts  of  com- 
mon resin,  shellac,  and  Venice  turpentine,  are  to  be  mixed 
together,  and  heated  in  a  metallic  vessel,  the  mixture  being 
retained  in  a  state  effusion  at  temperatures  from  230°  to  240°, 
until  all  evolution  of  vapour  has  ceased,  and  the  fluid  is  quiet. 
It  is  to  be  allowed  to  cool  until  it  thickens,  and  is  then  to  be 
poured  tranquilly,  so  as  to  avoid  the  formation  of  air  bubbles, 

*  In  December  1829  the  Editor  formed  an  electrical  accumulator,  by  roll- 
ing up  two  pieces  of  tin  foil  between  two  pieces  of  sheet  gum  elastic,  and  bring- 
ing out  the  ends  of  the  tin  foil,  so  that  the  two  poles  were  placed  as  far  from  each 
other  as  possible. — ED. 


KLECTROPHOKUS —  CONSTRUCTION USE.  461 

upon  the  tin  foil  laid  out  as  before  described,  so  that,  when 
cold,  it  may  Form  a  cake  one  third  or  one  half  of  an  inch  in 
thickness.  The  tin  foil  should  ultimately  be  trimmed  round 
the  edge,  and,  if  convenient,  a  board  attached  to  the  cake  to 
serve  as  a  bottom,  and  prevent  accidental  fracture  or  injury. 
This  is  one  part  of  the  electrophorus  (1011). 

1008.  The  second  part  may  be  a  piece  of  flat  deal  board, 
one  third  or  one  half  of  an  inch  in  thickness ;  less  in  size  than 
the  cake  of  resin  by  an  inch,  or  an  inch  and  a  half  on  every 
side,  and  with  the  edges  rounded  and  smoothed.     This  board 
is  to  be  covered  with  pasted  tin  foil,  smoothly  laid  on,  espe- 
cially at  the  edges,  and  all  asperities  rubbed  down.     The 
smoothest  and  flattest  side  is  to  be  appropriated  to  meet  the 
surface  of  the  resinous  plate  :  a  piece  of  glass  tube,  about 
seven  or  eight  inches  long,  is  to  be  fixed  perpendicularly  on 
the  middle  of  the  other  side  to  serve  as  a  handle ;  and  towards 
the  edge  on  the  same  side  should  be  fixed  a  piece  of  thick 
brass  or  other  wire,  about  two  inches  long,  curved  outwards, 
and  terminated  at  its  upper  extremity  by  a  smooth  metal  ball. 
This  is  the  cover  of  the  electrophorus  (1011). 

1009.  Before  using  this   instrument,  the   resinous   plate 
should  be  warm  and  dry  and  placed  upon  its  board  in  a  conve- 
nient horizontal  position,  with  its  tin  foil  on  its  lower  surface 
connected  by  a  chain  or  wire  with  the  floor  of  the  place,  or 
with  neighbouring  metallic  bodies.     A  piece  of  warm  dry 
flannel  is  to  be  doubled  up  loosely  so  as  to  form  a  roll 
about  ten  inches  long ;  one  end  of  the  roll  is  to  be  held  in 
the  hand,  and   the  other  being  swung  round  in  an  inclined 
direction,  by  a  quick  motion  of  the  wrist,  is  to  strike  the 
surface  of  the  plate  in  an  oblique  manner  each  time  it  pas- 
ses, so  as  to  produce  an  effect  between  that  of  a  rub  and  a 
blow.     This  is  to  be  done  over  the  whole  surface  of  the 
warm  resinous  plate,  by  which  it  will  be  excited  electrically 
to  a  considerable  degree.     Having  previously  warmed  the 
cover  of  the  electrophorus,  it  should  now  be  lifted  by  the 
handle  and  placed  on  the  middle  of  the  plate;  if  the  knob  of 
the  cover  be  touched  when  all  is  in  order,  a  spark  will  pass 
between  it  and  the  finger.     The  cover  is  then  to  be  lifted 
by  the  handle  in  a  horizontal  direction,  and  when  two  or 


462  ELECTROPHORUS. 

three  inches  above  the  plate,  the  knob  upon  it  is  again  to  be 
touched  by  the  finger  or  a  ball,  when  a  spark  much  stronger 
than  the  former  will  be  occasioned ;  the  cover  is  again  to  be 
put  down,  when  a  third  spark  will  pass  between  the  knob 
and  the  knuckle ;  being  again  lifted  as  before,  a  spark  as 
strong  as  the  second  may  be  taken  from  it :  similar  effects 
will  follow  for  a  long  time  by  repetitions  of  the  process. 
All  the  sparks  "which  pass  immediately  after  putting  the 
cover  down  are  negative  as  to  the  approximated  ball  or 
knuckle,  and  those  which  pass  after  taking  it  up  are  positive. 
1010.  When  the  electrophorus  is  in  good  order,  the  sparks 
taken  after  lifting  the  cover  are  quite  sufficient  to  inflame 
the  greater  number  of  explosive  mixtures  operated  upon  in 
eudiometers.  All  that  is  necessary  is,  to  substitute  the  knob 
of  the  cover  for  the  conductor  of  the  electrical  machine.  If 
a  stronger  spark  be  required,  a  jar  must  be  charged :  this 
may  be  done  either  positively  or  negatively,  at  pleasure. 
For  the  first  purpose  it  is  only  necessary  to  bring  the  knob 
of  the  electrophorus  cover  into  contact  with  the  knob  of  the 
jar  immediately  after  raising  it  from  the  plate;  upon  doing 
this  thirty  or  forty  times  in  succession,  the  jar  will  be  charg- 
ed positively :  if  the  ball  of  the  jar  be  applied  to  the  knob  of 
the  cover  each  time  the  latter  is  put  down,  until  several 
sparks  have  passed,  it  will  become  negatively  charged.  It 
must  be  understood,  that  to  obtain  strong  positive  sparks,  it 
is  necessary  to  touch  the  cover  when  on  the  resinous  plate 
with  a  finger  or  other  conducting  body,  which  must  be  re- 
moved before  the  cover  is  raised;  and  that  to  obtain  the 
strongest  negative  sparks,  the  cover  when  raised,  should  al- 
ways be  discharged  of  all  its  electricity  against  the  hand  or 
some  other  convenient  conductor,  before  it  is  again  placed 
on  the  plate.  The  cover  must  always  be  in  a  good  state  of 
insulation,  when  it  is  put  down  to  give  negative  sparks,  or 
when  it  is  taken  up  to  give  positive  sparks;  and  inasmuch  as 
ordinary  glass  has  a  powerful  tendency  to  attract  moisture  to 
its  surface,  and  thus  becomes  a  bad  insulator,  it  is  advisa- 
ble to  varnish  the  glass  tube  handle  with  sealing-wax  dis- 
solved in  spirit  of  wine,  or  to  construct  the  handle  of  a 
stick  of  sealing-wax  or  other  resinous  matter. 


SUBSTITUTES  FOR  THE  RESINOUS  PLATE.  463 

1011.  Instead  of  a  resinous  electrophoms  plate,  that  part 
of  the  instrument  may  be  made  of  a  sheet  of  thin  crown- 
glass,  the  metallic  base  (1007),  which  is  essential  as  a  bot- 
tom for  the  apparatus,  being  tin  foil  pasted  and  attached  to 
it.     A   large  plate  of  mica  without  fissures,  coated  in  the 
same  manner  with  tin  foil  on  one  side,  makes  a  most  excel- 
lent electrophorus.     The  cover  (1008),  instead  of  a  board, 
may  consist  of  a  plate  of  tin  having  its  edges  turned  up 
round  a  thick  wire,  that  no  sharp  edge  or  angle  may  be  pre- 
sented outwards.     These  parts  are  to  be  used  exactly  in  the 
manner  already  described  ;  but  if  glass  be  the  substance  em- 
ployed, it  must  be  well  warmed  at  first,  and  kept  warm  du- 
ring the  experiments.     It  is  most  powerfully  excited  by  be- 
ing rubbed  with  a  piece  of  silk,  having  some  amalgam  spread 
upon  it  (981) ;  this  should  be  p'assed  briskly  over  its  surface 
backward  and  forward,  and  at  last  slidden  rapidly  off  at  the 
edge,  so  as  not  to  rest  upon  any  one  part  of  the  glass,  as  it 
would  then  discharge  that  portion  of  its  surface.* 

1012.  Bennet's  gold  leaf  electrometer,  as  improved  by 
Singer,  is  highly  useful  in  the  laboratory,  for  the  facilities  it 
affords  of  detecting  electricities  of  low  tension,  and  deter- 
mining their  kind.    These  are  constantly  developed  by  chemi- 
cal action ;  by  the  voltaic  pile ;  and  by  other  causes  which 
are  related  to  chemical  science.     This  instrument,  as  im- 
proved by  the  application  of  Singer's  mode  of  insulating  the 
cap  and  gold    leaves,  will,  when  warm  and  dry,  retain  a 
charge  for  hours.     It  would  be  improper  to  enter  minutely 
into  its  applications;  but  repeated  experience,  that  its  indi- 
cations are  not  generally  well  understood  by  persons  having 
occasion  to  use  it,  induces  me  to  describe  more  particularly 
the  kind  of  change  it  receives  under  different  circumstances, 
and  the    precautions  requisite  in  interpreting  the  appear- 
ances. 

1013.  If  an  insulated  portion  of  conducting  matter,  as  a 

*  A  thin  gum-elastic  bag,  inflated  from  ether,  is  easily  excited  by  friction  with 
a  silk  handkerchief,  and  affords,  in  favourable  w.eather,  sparks  which  will  cause 
the  explosion  of  a  mixture  of  hydrogen  with  common  air,  or  oxygen.  By  ap- 
plying to  such  an  excited  bag  the  insulated  cover  of  an  electrophorus,  still 
stronger  sparks  may  be  elicited.— ED. 


464 

brass  ball  at  the  end  of  a  glass  handle  or  silken  thread,  be 
electrified,  and  then  placed  in  contact  with  the  cap  of  the 
electrometer,  the  cap  and  leaves  will  immediately  partake 
of  the  electricity  of  the  ball,  and  the  leaves  will  diverge. 
If  the  charge  in  the  ball  be  of  considerable  intensity,  the 
leaves  will  be  torn  to  pieces  by  their  mutual  repulsion,  and 
the  attraction  of  the  sides  of  the  glass  jar  ;  but  if  the  inten- 
sity be  small,  the  leaves  will  diverge  moderately,  so  as  not 
to  touch  the  glass ;  and  the  degree  of  divergence  will  be  in 
some  proportion  to  the  intensity  of  the  charge  communi- 
cated. The  appearances  will  be  the  same  whether  the  elec- 
tricity communicated  be  positive  or  negative. 

1014.  The   circumstances  will  be  different  if  the  body 
brought  in  contact  with  the  electrometer  is  an  electrified 
portion  of  what  is  usually  called  non-conducting  matter ;  if 
for  instance  it  be  a  stick  of  sealing-wax  rubbed  with  flannel, 
instead  of  a  metallic  ball.     If  highly  electrified,  this  will 
cause  the  same  disturbance  and  appearances  in  the  leaves 
during  its  approach  as  the  ball ;  if  moderately  electrified  it 
will,  when  in  contact  with  the  cap,  cause  the  usual  appear- 
ance of  divergence  in  the  leaves,  but  upon  removing  it,  the 
leaves,  instead  of  remaining  diverged,  will  either  collapse, 
or  remain  very  slightly,  and  frequently  uncertainly,  electri- 
fied.    This  is  a  consequence  of  the  non-conducting  power 
of  the  wax;  and  the  method  of  transferring  electricity  to  the 
electrometer  in  such  a  case  is,  to  draw  the  excited  parts  of 
the  wax  over  the  edge  of  the  cap ;  small  portions  will  be 
communicated,  and  the  electrometer  will  be  left  electrified 
similarly  to  the  wax.     Such  a  process  is,  however,  very  un- 
certain ;  for  if  the  electricity  of  the  wax  be  weak,  the  friction 
of  the  substance  against  the  electrometer  cap  will  sometimes 
generate  an  electricity  stronger  than  that  previously  existing 
on  the  surface  of  the  wax,  and  the  electrometer  will  become 
charged,  not  by  the  previous  electricity  of  the  wax,  but  by 
that  produced  during  its  friction  against  the  cap. 

1015.  This  difficulty  ruay,  however,  be  avoided  in  most  cir- 
cumstances, simply  by  bringing  the  electrified  non-conductor 
into  contact  with  the  cap,  and  retaining  it  there  during  the 
experiment;  for  the  electricity  which  in  this  way  is  made  by 


GOLD-LEAF  ELECTROMETER.  465 

induction  to  exist  in  the  leaves,  and  causes  their  divergence,  is 
the  same  as  that  which  would  exist  over  the  whole  of  the  cap 
and  leaves,  if  the  electricity  of  the  wax  could  be  transferred  to 
them. 

1016.  Such  are  the  circumstances  relating  to  the  charge  of 
the  electrometer,  by  bodies  brought  into  contact  with  it,  and 
communicating  to  it  part  of  the  electricity  they  previously 
possessed.     As  before  mentioned,  when  highly  electrified, 
they  cannot  be  so  applied  to  the  instrument  without  tearing 
the  leaves  to  pieces;  butthey  may  then,  when  held  ata  distance 
be  made  to  diverge  the  leaves  by  induction,  and  even  to 
communicate  a  charge  to  the  instrument,  and  thus  enable  it  to 
exhibit  divergencies  when  the  inducing  electrified  body  is  re- 
moved.  The  effects  thus  produced  by  induction  are  the  same 
in  kind  and  nearly  in  extent,  whether  the  electrified  body  be  a 
mass  of  conducting  or  non-conducting  matter,  so  that  in  this 
respect  the  metallic  ball  and  the  stick  of  wax  are  equal;  the 
only  difference  being  in  the  kind  of  electricity  produced, 
which,  with  bodies  charged  positively,  is  the  reverse  of  that 
occasioned  by  such  as  are  charged  negatively. 

1017.  When  an  electrified  substance  is  placed  at  such  a 
distance  from  the  cap  of  the  electrometer,  as  to  occasion  con 
siderable  divergence,  and  is  retained  there  for  a  few  minutes, 
the  divergence  of  the  leaves  will  generally  diminish,  and  the 
more  rapidly  as  the  instrument  becomes  cold  or  the  glass 
damp,  as  the  leaves  are  ragged,  or  any  part  of  the  cap  angular 
and  pointed.  On  removing  gradually  the  electrified  substance 
to  such  a  distance  that  it  can  no  longer  affect  the  instru- 
ment, it  will  be  found  that  the  leaves  will  collapse  at  first, 
and  afterwards  expand  again  more  or  less,  according  as  they 
had  lost  more  or  less  of  their  first  divergence.     This  ultimate 
divergence  of  the  leaves  will  be  due  to  a  charge  of  electricity 
in  the  instrument,  of  the  opposite  kind  to  that  of  the  inducing 
or  approximated  body. 

1018.  If  no  effect  of  this  kind  takes  place,  and  there  be  no 
diminution  of  the  first  divergence,  nor  any  ultimate  change, 
then  the  insulation  and  goodness  of  the  electrometer  is  proved 
by  a  powerful  test.     This  being  ascertained,  then,  if  whilst 
the  electrified  body  is  in  the  neighbourhood,  and  the  leaves 

3  I 


466  ELECTROMETER. 

diverged,  the  cap  be  touched  by  the  hand,  or  any  other 
conducting  substance  communicating  with  the  earth,  the 
divergence  of  the  leaves  will  instantly  cease.  In  this  state 
of  the  instrument,  if  the  communication  be  broken,  so  as  to 
leave  the  cap  ano!  leaves  insulated,  they  will  still  remain 
collapsed;  but  if  the  inducing  electrified  body  be  now  removed 
from  the  situation  in  which  it  at  first  caused  the  divergence, 
the  leaves  will  immediately  diverge,  and  the  electrometer 
become  charged  with  electricity  of  the  opposite  kind  to  that 
of  the  inducing  body.  The  degree  of  charge  thus  given  to 
the  instrument  will  be  in  proportion  to  the  degree  of  divergence 
induced  in  the  leaves  before  they  were  made  to  collapse  by 
the  touch  of  the  finger. 

1019.  In  the  case  in  which  a  weakly   electrified    non- 
conducting substance  was  directed  to  be  laid  on  the  cap  of 
the  electrometer  (101 5),  to  occasion  adivergence  by  electricity 
like  its  own,  it  may  be  observed  that,  if,  during  the  experi- 
ment, the  cap  be  touched  by  the  fingers,  and  the  electrified 
body  afterwards  removed,  the  leaves  will  first  collapse  and 
then  diverge   with  opposite  electricity,  although  at  the  com- 
mencement of  the  experiment  they  were  diverged  with  the 
same  electricity  as  that  of  the  body  to  be  examined. 

1020.  If  therefore  the  electricity  of  an  excited  body  is  to 
be  examined,  the  leaves  of  the  electrometer  are  in  the  first 
place  to  be  diverged.     This  may  be  done  with  the  same 
electricity,  by  bringing  the  body,  if  weakly  electrified,  into 
contact  with  the  cap,  leaving  it  there  if  of  non-conducting 
matter  (1015),  or  removing  it  after  contact  if  of  conducting 
matter  (1013);  or,  if  strongly  electrified,  by  approaching  it  so 
near  as  to  cause  a  sufficient  divergence  of  the  leaves,  and 
retaining  it  there  until  the  conclusion  of  the  experiment. 
On  other  occasions  however  with  strongly  excited  bodies,  it 
may  be  convenient,  either  because  of  their  size  or  other  cir- 
cumstances, to  communicate  a  charge  of  the  opposite  kind, 
in  the  manner  described  (1018) ;   then  upon  determining 
what  that  kind  is,  in  the  manner  to  be  immediately  described, 
the  electricity  of  the  originally  electrified  body  will  of  course 
be  known  to  be  opposite  to  it. 

1021.  The  tests  of  the  kind  of  electricity  by  which  the 


ELECTROMETER — CONDENSER.  467 

leaves  are  diverged,  are  of  the  following  nature.  A  stick  of 
sealing-wax  rubbed  with  warm  flannel  becomes  negatively 
electrified ;  a  tube  of  warm  glass  rubbed  with  a  dry  silk 
handkerchief,  or,  better  still,  with  a  piece  of  silk,  having  a  lit- 
tle amalgam  upon  it  (98 1  ),becomespositivety  electrified;  both 
these  excitations  being  so  strong,  as  to  make  the  leaves  of 
an  uncharged  electrometer  diverge,  whilst  the  wax  or  glass 
is  at  a  considerable  distance.  If  one  of  these  excited  sub- 
stances be  brought  near  the  cap  of  an  electrometer  already 
diverged,  it  will  either  cause  the  divergence  to  increase  or 
diminish.  The  divergence  will  increase  if  due  to  electricity 
of  the  same  kind  as  that  of  the  body  approached,  but  w\\\  di- 
minish if  of  the  opposite  kind;  so  that  the  electricity  of  the 
body  approached  being  known,  that  of  the  electrometer  will 
also  be  known,  and  consequently  that  of  the  excited  body 
which  had  originally  caused  its  divergence.  The  sealing- 
wax  for  instance  is  rendered  negative  by  flannel :  being  ap- 
proached to  a  diverged  electrometer,  it  may  cause  the  leaves 
to  collapse;  the  conclusion  to  be  drawn  is,  that  the  electro- 
meter leaves  were  in  a  positive  state  :  being  approached  to 
another  diverged  electrometer  it  may  increase  the  divergence, 
in  which  case  it  will  indicate  that  the  leaves  of  the  electro- 
meter were  in  a  negative  state.  An  excited  rod  of  glass 
brought  to  these  electrometers  would  make  the  first  diverge 
still  more,  and  would  cause  the  second  to  collapse,  in  both 
cases  indicating  the  same  states  as  the  wax.* 

1022.  Some  precaution  is  required  with  respect  to  the 
manner  in  which  these  excited  rods  are  to  be  applied.  The 
electrometer  being  diverged,  the  wax  or  glass  is  to  be  ex- 

*  The  author,  from  the  vast  magazine  of  devices,  sometimes  omits  the  selection 
of  some,  which,  neither, want  of  room  nor  inadvertency  should  have  excluded. 
Among  these  are  electrical  condensers.  A  condenser  is  now  usually  attached  to 
gold-leaf  electrometers,  and  properly  so,  because  it  increases  greatly  the  delicacy 
of  their  action.  That  condenser  consists  of  a  metallic  plate  connected  by  a 
hinged  foot-stalk  with  the  earth,  which  when  brought  close  to,  but  not  into  contact 
with,  a  similar  plate  attached  to  the  cap,  enables  the  cap  to  receive  from  the  elec- 
trified body  a  stronger  charge  which  is  rendered  visible  by  the  subsequent  re- 
moval of  the  moveable  plate.  The  contact  of  the  two  plates  is  prevented  by  var- 
nish, or  sealing-wax,  or  mica.  Professor  Johnson  of  the  Franklin  Institute  was 
the  first  to  use  sheet  gum  elastic  for  the  cover  of  condensers  of  all  sorts.  His 
paper  on  that  subject  may  be  found  in  Silliman's  Journal. — ED. 


468  ELECTROMETER. 

cited  at  such  a  distance  as  to  have  no  influence  over  the  in- 
strument; the  most  strongly  excited  part  of  the  wax  or  glass 
is  then  to  be  gradually  approached  to  the  cap,  the  hand  and 
all  other  unnecessary  conducting  bodies  being  kept  out  of 
the  way  as  much  as  possible,  or  at  least  not  moved  into  the 
neighbourhood  of  the  electrometer  during  the  experiment. 
As  soon  as  the  rod  begins  to  effect  the  leaves  (even  though 
the  distance  be  two  or  three  feet),  the  aifect  must  be  watch- 
ed, and  then  their  collapse  or  further  divergence  will  become 
evident  immediately  on  moving  the  rod  a  little  way  to  or 
from  the  instrument.     It  is  this  first  effect  that  indicates  the 
kind  of  electricity  in  the  electrometer,  and  not  any  stronger 
one;  for  although,  if  the  repulsion  be  increased  from  the 
first,  no  approach  will  cause  a  collapse  to  take  place  except 
the  actual  discharge  of  the  leaves  against  the  sides  of  the 
glass,  yet  where  collapse  is  the  first  effect,  it  may  soon  be 
completed,  and  a  repulsion  afterwards  occasioned  from  a  too 
near  approach  of  the  strongly  excited  test  tube.     It  is  there- 
fore, the  first  visible  effect  that  occurs,  as  the  test  rod  is  made 
to  approach  from  a  distance,  that  indicates  the  nature  of  the 
electricity;  and  when  this  effect  is  observed,  the  rod  should 
not  be  brought  nearer,  so  as  permanently  to  disturb  the  state 
of  the  electrometer,  but  should  be  removed  to  a  distance, 
and  again  approached,  for  the  purpose  of  repeating  and  veri- 
fying the  preceding  observation. 

1023.  It  is  to  be  understood,  that  the  approach  of  the  test 
rod,  though  it  affects  the  divergence,  causes  no  permanent 
change  of  the  electricity  in   the  instrument,  unless  it  be 
brought  much  too  near,  and  cause  considerable  disturbance 
of  the  leaves.     The  electrometer  will  remain,  after  a  good 
experiment,  in  the  same  state  as  at  first  (1018). 

1024.  When  the  body  to  be  examined  is  so  strongly  elec- 
trified that  it  may  not  be  brought  near  to  the  electrometer, 
but  has  been  placed  at  such  a  distance  as  to  affect  it  (1020), 
and  left  there  to  cause  a  proper  divergence,  then  its  place 
should  not  be  directly  over  but  rather  on  one  side  the  cap, 
that  the  test  tube,  when  applied  may  be  brought  towards 
the  instrument  on  the  other  side;  the  originally  electrified 


ELECTROSCOPES VOLTAIC  ELECTRICITY.  469 

body  and  the  test  tube  being  retained  in  directions  as  widely 
apart  as  they  conveniently  can  be.* 

§  2.  Voltaic  Electricity. 

1025.  Great  variety  in    the  forms  of  the  Voltaic   pile, 
trough,  or  battery  have  been  introduced  at  different  times, 
of  which  a  knowledge  may  be  obtained  from  elementary 
works  on  Chemistry  or  Electricity,  and  from  particular  me- 
moirs on  the  subject.     The  information  here  to  be  conveyed 
does  not  concern  these  varieties  of  form  so  much  as  the  man- 
agement by  which  they  are  to  be  rendered  serviceable  and 
effectual  in  the  performance  of  experiments.     This  manage- 
ment, though  it  be  spoken  of  generally,  will  be  described 
with  reference,    principally,  to  the  ordinary  form   of  ap- 
paratus, in  which  the  plates  being  arranged  in  sets  of  ten 
each,  and  fixed  to  a  bar  of  wood,  are  inserted  into  earthen- 
ware troughs,  as  suggested  by  Dr  Babington. 

1026.  Troughs  are  usually  charged  with  a  diluted  mixture 
of  acids,  which,  when  the  plates  are  immersed,  confers  power 
and  activity  upon  the  arrangement.     A  mixture  of  a  proper 
strength  is  obtained  by  adding  two  parts  in  bulk  of  oil  of 
vitriol  and  one  part  of  common  nitric  acid  to  80  or  100  parts 
of  water,  the  whole  being  well  stirred  together  until  equally 
mixed.     Its  power  should  in  all  cases  be  ascertained  before 
it  is  poured  into  the  troughs,  by  dipping  a  piece  of  clean 

*  Coulomb's  electroscope  is  more  delicate  than  Bennett's.  It  consists  of  a 
needle  of  shell-lac  suspended  horizontally  by  the  fibre  of  the  silk-worm.  Hare's 
single  leaf  electrometer  is  so  constructed  as  to  permit  the  space  between  the  leaf 
and  a  metallic  ball  to  be  changed  at  pleasure,  is  delicately  graduated,  so  as  not  only 
to  display  slight  excitation,  but  also  to  measure  its  intensity. 

For  common  purposes,  a  very  good  electrometer  is  formed  of  a  very  small  ca- 
outchouc bag  made  of  a  small  section  of  the  sheet,  blown  out  until  perfectly 
transparent.  Tied  by  its  neck  to  the  middle  of  a  vertical  silk  fibre  kept  on  the 
stretch,  the  bag  will  project  from  the  string  in  a  horizontal  direction.  The  slight- 
est blow  with  the  end  of  a  silk  handkerchief  renders  the  bag  electro-negative  and 
gives  to  it  the  power  of  showing  by  its  motion  the  character  of  the  electricity  of 
the  body  to  be  examined.  So  tenacious  is  the  electrical  excitement  that  a  bag 
has  remained  attached  to  an  oppositely  electrified  surface  for  two  weeks,  in  very 
unfavourable  weather.  The  editor  demonstrated  this  curious  power  to  Professor 
Johnson,  Professor  Bache  and  several  other  scientific  gentlemen. — ED. 


470  VOLTAIC  TROUGH — ACID  MIXTURE. 

zinc  into  a  little  of  it  in  a  glass  and  observing  the  degree  of 
action  exerted  upon  the  metal.  A  stream  of  bubbles  should 
be  disengaged  so  small  that  their  size  can  hardly  be  distin- 
guished by  the  naked  eye,  and  which,  as  they  rise  up  through 
the  fluid,  should  be  carried  freely  in  different  directions  by 
the  currents  in  the  fluid  itself.  If  the  action  be  so  strong 
as  to  evolve  bubbles  of  a  considerable  size,  which  rapidly 
rise  to  the  surface,  and  are  numerous,  the  acid  must  be  di- 
luted. If,  on  the  contrary,  little  or  no  chemical  action  can 
be  perceived,  the  charge  must  be  strengthened  by  the  ad- 
dition of  acid.  Although  the  above  charge  is  recommended 
for  ordinary  use,  it  may  frequently  be  necessary,  when  more 
energetic  action  is  required,  to  increase  the  proportion  of 
acid  accordingly. 

1027.  If  the  proportion  of  the  two  acids  differ  from  the 
above,  then  the  indications  by  bubbles  varies  also.     The  sul- 
phuric acid  causes  the  formation  of  bubbles  and  gas;  the 
nitric  acid  tends  to  prevent  the  formation  of  either  when 
present  within  certain  proportions  with  the  sulphuric  acid, 
and  a  mixture  which  evolves  much  gas  from  zinc  may  con- 
sequently have  the  evolution  lessened  by  the  addition  of  ni- 
tric acid,  although  at  the  same  time  its  exciting  power  in 
the  Voltaic  trough  is  increased.     Hence  it  is  often  useful  to 
increase  the  proportion  of  nitric  acid,  for  the  purpose  of 
avoiding  the  production  of  much  gas  or  vapour  from  the  bat- 
tery during  the  experiments. 

1028.  The  cells  are  to  be  filled  to  within  half  an  inch  of 
their  upper  edges ;  when  the  plates  are  in  their  places,  the 
mixture  should  not  flow  from  one  cell  into  another.     The 
fluid  in  the  cells  may  be  levelled,  and  made  equal  in  all,  by 
raising  the  trough  on  one  side,  so  that  the  liquid  may  flow 
from  one  cell  into  another  over  the  divisions ;  its  passage 
from  the  trough  is  prevented  by  the  height  of  the  edges  of 
the  latter  all  the  way  round  above  the  level  of  the  divisions. 
This  superior  height  of  the  edges  of  the  trough  is  atten- 
ded to  in  all  constructions  of  Voltaic  apparatus  with  cells, 
whether  formed  of  earthenware  or  whether  the  cells  are 
made  by  the  plates  themselves  set  at  equal  distances,  and 
cemented  into  a  trough  of  wood. 


IMMERSION  OF  THE  PLATES PRECAUTIONS.      471 

1029.  When  the  plates  of  the  battery  are  separate  from 
the  troughs,  and  are  to  be  immersed  after  the  latter  are  charg- 
ed with  fluid,  great  care  is  necessary  that  they  be  properly 
introduced ;   the  zinc  and  copper  plates  of  two  contiguous 
pairs  are  to  be  placed  in  the  same  cell,  but  not  the  zinc  and 
copper  plates  of  the  same  pair.     There  is  no  fear  of  erring 
on  this  point  with  Wollaston's  double  coppers,  but  when 
the  copper  plates  are  single,  considerable  risk  of  this  kind  is 
incurred.     It  is  also  essential  that  the  plates  be  arranged  in 
the  same  relative  position,  i.  e.  all  the  zinc  plates  in  one  di- 
rection, and  all  the  copper  plates  in  the  other.     When  by 
accident   10  pairs  of  plates  are  turned  the  wrong  way  in  a 
battery  of  100  or  more,  they  do  considerably  greater  harm 
than  merely  results  from  the  loss  of  their  own  power,  and 
the  neutralization  of  that  of  10  other  pairs.     It  is  always  ad- 
visable so  to  arrange  a  battery  that,  whatever  the  number  of 
troughs  may  be,,  the  two  extremes  of  the  series  should  be 
within  two  or  three  feet  of  each  other.     The  troughs  may 
stand  very  well  on  dry  boards;  and  no  material  loss  of  power 
will  occur,  if,  in  the  convolution  of  the  battery,  the  rows  are 
two  feet  apart,  unless  indeed  the  series  be  very  extensive. 
Damp  ground  or  damp  boards  occasion  considerable  loss  in 
the  power  of  extensive  batteries,  especially  if  the  intervals 
between  the  rows  are  small,  and  the  wires  of  communication 
for  the  experiments  thin  and  long  (1036). 

1030.  When  the  battery  is  charged,  and  the  plates  im- 
mersed in  the  acid,  the  good  order  of  the  whole  is  to  be  as- 
certained by  fastening  two  wires  to  the  extreme  plates  to 
serve  as  poles,  twisting  *  their  ends  round  two  pieces  of  well 
burned  box-wood  charcoal  (1033),  and  bringing  these  to- 
gether.    An  immediate  discharge  of  electricity  will  take 
place,  producing  an  exceedingly  brilliant  spark  of  light, 
which  will  be  larger  or  smaller  in  proportion  to  the  size  and 
power  of  the  battery.     If  therefore  it  be  wanting  altogether, 
or  by  no  means  equal  to  what  was  anticipated  from  a  trial 
with  a  single  trough  in  the  same  manner,  then  the  obstruc- 
tion, or  whatever  it  may  be  that  interferes,  is  to  be  sought 
for  by  the  following  method. 

*  See  note  to  (1036).— ED. 


472  ACTION  OF  THE  BATTER?  TESTED. 

1031.  A  piece  of  copper  wire  about  the  ¥^  of  an  inch  in 
diameter,  and  four  or  five  feet  in  length,  is  to  have  one  end 
twisted  round  a  piece  of  box-wood  charcoal,  and  the  other 
brightened  ;  then  beginning  at  one  extremity  of  the  battery, 
the  bright  end  is  to  be  pressed  tightly  against  the  last  plate 
with  one  hand,  whilst  by  means  of  the  other  the  corner  of 
some  plate,  as  far  off  as  can  be  conveniently  reached,  is  to 
be  touched  with  the  charcoal  at  the  opposite  extremity.     If 
the  spark  be  as  brilliant  as  could  be  expected,  it  will  prove 
the  perfection  of  the  arrangement  through  the  portion  tried. 
The  bright  end  of  the  wire  is  then  to  be  brought  to  the  plate 
last  touched,  and  a  second  portion  of  the  battery  tried  in 
the  same  manner,  until  the  whole  has  been  tested.     If,  du- 
ring the  trial,  the  discharge  of  any  portion  seems  imperfect, 
or  is  altogether  wanting,  then,  keeping  the  bright  end  of  the 
wire  against  the  plate  with  which  it  was  in  contact  at  the 
time  of  the  failure,  every  fifth  or  sixth  plate  is  to  be  tried 
backwards   with  the  charcoal,  which  is  to  approximate  at 
each  remove  that  to  which  the  bright  end  is  applied,  and  it 
will  be  found  that  on  a  sudden  the  discharge  is  effected, 
though  with  less  force,  because  of  the  smaller  number  of 
plates  between  the  ends  of  the  wire.     Whenever  this  dis- 
charge occurs,  it  points  out  the  place  where,  from  some  de- 
rangement or  untoward  circumstance,  the  obstacle  to  the  ac- 
tion of  the  battery  exists. 

1032.  The  battery  is  to  be  examined  at  this  point,  and  it 
will  be  found  that  a  plate  is  in  the  wrong  trough ;  or  that 
acid  is  wanting ;  or  that  a  wire  lies  across  to  some  other  part 
of  the  arrangement;  or  that  the  metallic  communication  is 
bad,  the  zinc  plate  being  either  broken  or  injured  by  corro- 
sion; or  some  other  cause  for  the  obstruction  will  be  found. 
This  must  be  removed,  or  if  it  be  of  such  a  nature  that  it 
cannot  immediately  be  corrected,  either  the  trough  where  it 
occurs  must  be  rejected,  or  a  good  metallic  connexion  by 
thick  copper  wire  (1034)  must  be  made  between  the  plates 
on  different  sides  of  the  obstruction,  so  as  to  allow  an  effi- 
cient and  concurring  action  of  the  rest  of  the  battery.     This 
trial  of  the  battery  need  not  necessarily  be  made  on  portions 
of  four  or  five  feet,  but  when,  from  the  convolution  of  its 


VOLTAIC  BATTERY CHARCOAL.  473 

course,  an  opportunity  is  offered  of  connecting  the  battery 
across,  more  extensive  portions  may  be  tried,  as,  for  instance 
one  half  at  a  time,  and  thus  the  half  containing  the  obstruc- 
tion may  be  at  once  discovered. 

1033.  The  charcoal  used  in  these  and  similar  experiments, 
with  the  Voltaic  battery,  is  made  from  box-wood,  which  be- 
ing cut  into  pieces,  having  a  length  of  two  inches,  and  a 
thickness  of  about  a  quarter  of  an  inch,  is  to  be  charred  in 
close  vessels.     The  wood  may  be  packed  in  an  earthenware 
crucible,  and  being  well  covered  over  with  dry  sand,  should 
be  heated  until  it  ceases  to  flame.     Although  the  greater 
part  of  such  charcoal  will  conduct  electricity  almost  as  well 
as  metals,  some  pieces  will  probably  fail.     Before  being  set 
aside,  therefore  for  use,  it  should  be  examined  by  a  single 
trough,  a  wire  being  brought  from  each  end  of  the  trough, 
against  the  opposite  ends  of  each  piece  of  charcoal  in  suc- 
cession.    Such  as  easily  conduct  the  electricity,  and  yield  a 
brilliant  spark,  are  to  be  preserved  in  a  stoppered  bottle; 
those  which  afford  a  small  spark,  or  none,  should  be  rejected. 

1034.  When  two  or  more  troughs  are  to  be  connected, 
and  the  instrument-maker  has  not  furnished  the  necessary 
means  attached  to  the  sets  of  plates,  the  arrangement  should 
first  be  examined  to  ascertain  that  the  plates  of  both  troughs 
are  placed  in  the  same  relative  position  and  order,  and  when 
that  is  the  case  they  may  be  connected,  and  considered  but 
as  one  trough.     The  connexion  should  be  made  by  a  single 
or  double  copper  wire,  not  less  than  one  fifth  of  an   inch 
in  diameter ;  and  the  operator  should  not  be  satisfied  with 
merely  bending  the  wire,  so  that  the  ends  may  drop  into  the 
two  cells  containing  the  plates  to  be  connected,  but  should 
bring  them  into  firm  and  close  contact  with  the  plates  in 
those  cells,  so  that  a  good  metallic  communication  may  exist 
between  them.     If  the  ends  of  the  wires  merely  dip  into  the 
fluid  charge  of  the  cell,  which,  in  comparison  to  the  metal 
of  the  apparatus,  is  a  bad  conductor  of  electricity,  then  all 
the  electricity  has  to  pass  from  the  fluid  to  the  wire  by  a 
very  small  surface;  it  has  consequently  to  pass  through  a 
great  length  of  the  badly-conducting  body,  and  also,  near 
the  wire,  has  to  be  compressed  as  it  were  into  a  small  mass. 

3K 


474  VOLTAIC  BATTERY ITS  POLES. 

,  y 
of  it:  both  of  which  are  circumstances  causing  obstruction 

to  its  course,  and  waste  of  power  in  the  battery.  But,  on 
the  contrary,  if  the  wire  touch  the  metallic  plate,  the  elec- 
tricity then  passes,  comparatively  without  obstruction.  Nor 
is  it  retarded  importantly  when  the  wires  are  soldered  to 
plates  equal  in  size  to  those  of  the  troughs,  even  though  they 
may  not  touch  the  trough  plates,  for  then  a  large  surface  of 
metal  is  afforded  for  contact  with  the  liquid,  and,  conse- 
quently, for  the  transmission  of  the  electricity  :  the  stratum 
of  fluid  between  the  communicating  plate  and  the  trough 
plate  is,  virtually,  not  a  fifth  or  sixth  of  its  former  quantity; 
and  the  additional  plates  also  are  active,  like  the  other 
plates  of  the  trough.  When  these  communicating  wires 
with  plates  at  their  extremities  are  not  at  hand,  ordinary 
wires  are  to  be  used,  and  brought  into  contact  with  the  plates 
already  in  the  cells :  this  is  easily  done  by  bending  the  wires, 
so  that  when  introduced  into  the  cells  they  may  act  as  springs, 
and  press  against  the  plates. 

1035.  The  two  extremes  of  the  whole  arrangement  are 
called  the  poles,  and  require  to  be  connected  in  various  ways 
with  the  solids  and  fluids  to  be  acted  upon,  according  to  the 
nature  of  the  experiments.     Metallic  rods  or  thick  wires  are 
usually  made  to  proceed  from  these  extremes,  and,  as  long 
as  they  remain  in  communication  with  them,  are  often  termed 
the  poles.    It  is  essential  that  these  pole-wires  should  com- 
municate with  the  extremes  of  the  battery,  either  by  plates 
at  their  extremities,  equally  large  with  those  oftthe  bat- 
tery, or  by  actual  and  good  metallic  contact  with  the  end 
plates  of  the  series.     The  simple  immersion  of  their  extrem- 
ities in  the  fluid  of  the  extreme  cells  should  never  be  con- 
sidered as  sufficient  (1034). 

1036.  These  poles  or  terminal  wires  should  be  of  con- 
siderable thickness.     Copper  wire  (1034)  one  fifth  of  an  inch 
in  diameter,  answers  the  purpose  very  well  in  ordinary  ca- 
ses.    In  experiments,  when,  from  the  rigidity  of  such  wire, 
it  may  be  found  necessary  to  complete  the  communication 
with  the  substance   to  be  experimented  upon  by  a  smaller 
wire,  still  the  thicker  one  should  be  continued  as  far  as  pos- 
ible,  and    the   small  wire  made    short.      Even   the   large 
wires,  which  conduct  the  electricity  from  the  battery  to  the 


• 


VOLTAIC  POLES THEIR  SIZE.  475 

substance  under  examination,  should  be  as  short  as  conveni- 
ent; for  though  with  electricity  of  considerable  intensity 
they  may  seem  to  cause  no  obstruction,  yet  when  of  slight 
power  they  will  offer  considerable  resistance.  Metals  them- 
selves vary  much  in  their  power  of  conducting  electricity,  but 
no  one  of  them  is  more  advantageous  for  the  purpose  of  effect- 
ing Voltaic  communications  than  copper  (1347) :  it  is  easily 
drawn  into  wire;  is  very  flexible;  has  a  high  conducting 
power;  and  when  pure  and  in  a  state  of  rest,  exhibits  no 
magnetic  effects,  and  consequently  does  not  interfere  with 
the  magnetic  phenomena  occasioned  by  a  current  of  elec- 
tricity passing  through  it. 

1037.  When   Voltaic   electricity  is  resorted  to  for    its 
chemical    power  over  imperfectly  conducting    matter  (on 
which  only  it  has  hitherto  been  rendered  efficient),  the  sub- 
stance to  be  acted  upon  is  placed  between  the  two  poles  or 
extremes  of  the  wires,  being  made  the  medium  of  conducting 
communication  from  the  one  to  the  other.     These  extremes 
are  best  formed  of  platinum,  which,  of  all  the  metals,  is  the 
one  least  acted  upon  by  the  substances  likely  to  be  opera- 
ted   with  or  evolved.     The  nearer  those  extremes  or  ac- 
ting poles  are  to  each  other,  i.  e.  the  smaller  the  portion  of 
imperfectly  conducting    matter    between    them,  the   more 
powerfully  is  it  affected;  and  the  same  holds  good  to  a  cer- 
tain extent,  with  respect  to  the  size  of  these  poles,  for  the 
greater  the  surface  of  their  contact  with  the  matter  to  be 
decomposed,  the  greater  is  the  action,  provided  the  distance 
between  the  two  surfaces  be  not  increased.  (1052,  <fcc.) 

1038.  These  remarks  are  intended  to  apply  to  an  extent 
of  the  acting  surfaces,  considerably  less  than  the  size  of  the 
plates  of  the  battery,  and  they  become  more  applicable, 
when  the  substance  acted  upon  is  a  worse  conductor  of  elec- 
tricity.    Thus  suppose  a  battery  of  100  pair  of  plates  of  four 
inches  square  to  be  in  use,  and  water  were  to  be  placed  be- 
tween the  poles  for  decomposition ;  then,  instead  of  holding 
the  poles,  which  may  be  two  small  platinum  wires,  in  the 
water,  point  to  point,  half  an  inch  apart,  it  would  be  better 
to  hold  them  side  by  side  at  the  same  distance.     It  would  be 
better  still  to  use  two  slips  of  platinum  foil  instead  of  the 


476  POLES-^COMMUNICATION. 

wires,  placing  them  parallel  to  each  other  in  the  water,  and 
half  an  inch  apart;  and  if,  instead  of  half  an  inch,  the  distance 
were  one  fourth  of  an  inch,  or  still  less,  the  effect  would  be 
proportionably  increased.  Every  increase  in  size  of  these 
slips,  until  they  were  at  least  two-thirds  the  size  of  the  plates 
in  the  battery,  would  also  be  advantageous,  by  increasing 
the  surface  of  action  without  materially  diminishing  its  in- 
tensity. But  if  instead  of  water  a  very  strong  solution  of 
potash  were  the  substance  to  be  acted  upon,  then  though 
the  general  effect  would  be  the .  same,  and  the  advantage 
very  striking  by  the  substitution  of  small  plates  of  foil  for 
wire,  it  would  cease  if  the  plates  were  as  large  as  those  of 
the  battery,  or  even  of  a  size,  which  would  be  beneficial  if 
water  alone  was  used. 

1039.  It  is  essentially  necessary  that  the  metallic  com- 
munication between  the  battery  and  the  acting  poles,  or  the 
extremes  of  the  wires,  should  be  good  and  perfect.     In  any 
place  where  a  permanent  junction  may  be  allowed,  it  is  best 
to  effect  it  by  sound  metallic  soldering  or  brazing.     Where 
a  temporary  junction  only  is  required,  it  is  effected  by  bring- 
ing the  clean  surfaces  into  close  contact,  and  retaining  them 
so  for  the  time  by  pressure  or  otherwise.     Wires  may  be 
twisted  together,  their  surfaces  being  first  well  cleaned  and 
brightened;  or  if,  from  their  thickness,  they  are  stiff  and 
rigid,  they  should  be  first  slightly  twisted  together,  and  then 
bound  round  by  twenty  or  more  turns  of  clean  copper  wire 
of  smaller  size.*     Either  in  twisting  or  in  binding  wires, 
two  or  three  loose  turns  must  never  be  considered  as  suffi- 
cient, but  the  two  pieces  must  be  so  twisted  or  bound  to- 
gether, as  to  have  the  steadiness  of  one  piece. 

1040.  When  a  junction  is  required  to  be  made  and  broken 
again  frequently,  as  happens  in  many  electro-chemical  and 
electro-magnetical  experiments,  it  should  be  done  at  one 
place  only  in  the  metallic  communication.     The  ends  of  the 
wires  should  be  perfectly  clean,  and  when  put  across  each 
other  for  the  purpose  of  effecting  the  communication,  should 
be  held  tightly  in  the  hand,  or  pressed  together  by  a  weight 

*   The  small  hand-vices  are  a  great  improvement  on  the  means  of  junction. — 
ED. 


POLES METALLIC  CONTACT.  477 

placed  upon  them  for  the  time;  or  in  peculiar  situations, 
such  a  bend  must  be  given  to  the  wires  that  they  may  act 
as  springs  and  press  against  each  other.  It  is  often  advanta- 
geous to  amalgamate  the  surface  of  these  ends,  for  then,  if 
they  be  moistened  with  a  little  mercury,  the  fluid  metal 
causes  a  perfect  contact  over  a  comparatively  large  surface 
at  the  point  where  the  wires  meet,  the  moment  they  are  con- 
nected together. 

1041.  Clean  copper  wires  are  readily  amalgamated  on  the 
surface,  by  washing  them  with  a  solution  of  nitrate  of  mer- 
cury, then  rinsing  them   in  water  and   afterwards   dipping 
them  in  mercury.     When  the  experiments  are  of  long  con- 
tinuance, it  is  convenient  to  put  about  a  quarter  of  an  ounce, 
in  bulk,  of  mercury  into  a  cup  or  glass,  with  half  an  ounce 
by  measure  of  moderately  strong  solution  of  nitrate  of  mer- 
cury ;  on  cleaning  the  curved  end  of  the  wire  a  little,  dip- 
ping it  into  the  nitrate,  and  moving  it  about  in  contact  with 
the  solution  and  the  metal  beneathv  it  will  quickly  amalga- 
mate, after  which  it  should  be  removed  into  another  glass 
containing  water,  with  a  little  mercury  at  the  bottom,   the 
adhering  solution  washed  off,  and  the  wire  dried  by  a  piece 
of  bibulous  paper.     This  method  is  very  convenient  for  en- 
suring the  amalgamation  and  perfect  contact  of  chain  or 
link  joints,  by  which  the  necessary  mobility  of  part  of  the 
metallic  communication  in  electro-magnetic  experiments  is 
attained.     The  ends  of  wires  thus  amalgamated,  if  not  well 
washed,  frequently  oxidate,  and  become  covered  in  a  few 
days  with  a  thick  crust  of  badly  conducting  matter.     If,  from 
the  duration  of  the  experiments,  this  be  inconvenient,  the 
wjres  should  be  amalgamated,  not  by  nitrate  of  mercury, 
but  by  the  use  of  a  little  tallow  and  metallic  mercury,  putting 
the  tallow,  with  a  few  globules  of  the  metal,  on  a  piece   of 
chamois  leather,  and  rubbing  the  wire  with  it  until  the  ad- 
hesion is  effected.     Wires  thus  prepared  do  not  tarnish  or 
become  foul  nearly  so  soon  as  those  prepared  in  the  former 
method. 

1042.  Where  flat  surfaces  are  to  be  brought  into  contact, 
the  intervention  of  a  little  mercury  is  very   useful,  but  the 
surfaces  should  previously  be  well  cleaned,  and  if  amalga- 


478  •     POLES— HARE'S  CONJUNCTIVE  RODS. 

mated,  the  contact  is  more  secure.  A  cup  of  mercury  is  also 
convenient  for  making  metallic  communications,  which  re- 
quire to  be  broken  frequently,  for  which  purpose  the  ends 
of  the  two  wires  to  be  connected  should  be  cleaned,  amal- 
gamated and  dipped  into  the  metal.  The  wires  may  be 
readily  arranged,  so  that  one  may  be  displaced  and  restored, 
without  the  slightest  shake  or  disturbance  of  the  apparatus, 
and  the  perfection  of  the  contact  is  ensured  every  time  the 
wire  is  replaced. 

1043.  The  importance  of  these  four  points,  namely,  accu- 
rate metallic  contact ;  sufficiency  of  thickness  in  the  con- 
ducting wires;  their  shortness;  and  also  extent  of  surface 
where  a  good  conductor  and  a  bad  one  are  in   contact, 
should  never  be  forgotten  in  practice ;  and  though  one  or 
the  other,  or  most  of  them,  may  now  and  then  be  of  little  con- 
sequence in  particular  experiments,  yet  attention  to  them  is 
alwaysuseful,  and  often  essential.     This  is  especially  the  case 
in  electro-magnetic  experiments,  where  electricity  in  great 
quantity  but  of  low  intensity  is  frequently  the  subject  of  in- 
vestigation.    One  person  will  not  be  able  to  perform  electro- 
magnetic revolutions  and  motions  with  five  or  six  troughs, 
which  another,  by  attention,    to  these  circumstances,  will 
effect  with  a  single  pair  of  small  plates.* 

1044.  In  all  experiments  with  large  batteries  it  is  advisa- 
ble to  retain  only  one  of  the  poles  in  the  hand  at  a  6time 
^unless  indeed  they  are  previously  in  communication  with 
each  other  by  good  conducting  matter,  or  by  large  surfaces 
and  masses  of  badly  conducting  substances.     The  pole-wires 
should  be  preserved  distinct  from  each  other  in  all  parts  of 
their  course,  so  that  no  accidental  discharge  and  consequent 
waste  of  power  may  take  place  between  them.     For  tnis 
reason  both  should  not  be  allowed  to  come  in  contact  with 
the  same  piece  of  metal  or  wire,  or  be  connected  by  good 
or  even  moderately  conducting  matter.     All  their  energies 

*  Leaden  rods  of  about  three-eighths  of  an  inch  in  diameter,  to  the  ends  of 
which  small  hand-vices  are  soldered,  afford  the  greatest  flexibility,  most  complete 
contact,  and  are  in  most  respects  preferable  to  any  other  conjunctive  apparatus. 
Dr  Hare,  who  suggested  this  application  of  them,  uses  them  almost  exclusively. 
—En. 


VOLTAIC  BATTERY — DECOMPOSITION.  479 

should  be  preserved  unimpaired  until  they  are  exerted  upon 
the  substance  placed  purposely  for  decomposition  between 
their  extremities. 

1045.  In  all  cases  the  experiments  should  be  prepared  as 
far  as  possible  before  the  battery  is  put  into  action,  that  none 
of  its  power  may  be  unnecessarily  wasted  during  such  pre- 
paration. 

1046.  The  methods  of  subjecting  substances  to  the  poles 
of  the  battery  for  the  purpose  of  effecting  their  decomposi- 
tion, and  of  collecting  the  results,  are  very  numerous.     If 
the  substance  be  a  fluid,  for  example  water  or  a  saline  solu- 
tion, it  may  be  put  into  a  glass,  and  the  two  platinum  poles 
(1037)  immersed  in  it:  the  nearer  they  are  brought  to  each 
other  the  more  powerful  will  be  the  action.     Tubes   will 
answer  the  same  purpose.     They  may  be  prepared  very 
conveniently  for  such  experiments  by  closing  one  end,  but 

with  a  platinum  wire  passed  through  it,  ex- 
tending nearly  to  the  other  end.  This  may 
be  done  by  passing  the  wire  through  a  cork, 
and  using  that  cork  to  close  the  tube  ;  or  by 
sealing  the  platinum  wire  into  the  tube,  and 
at  the  same  time  closing  its  extremity  in  the 
manner  to  be  described  in  Section  xix  (1201). 
Such  a  tube  being  fixed  on  a  cork  (67)  with  its  open  end 
uppermost,  may  be  filled  with  the  fluid,  and  then,  if  one  pole 
be  brought  into  contact  with  the  external  end  of  the  tube 
wire,  and  the  other  pole  immersed  in  the  fluid,  action  im- 
mediately commences.  In  all  these  arrangements  it  is  ne- 
cessary, that  however  near  the  poles  may  approach  each 
other,  they  should  not  be  in  contact,  for  then  all  chemical 
action  on  the  surrounding  fluid  ceases. 

1047.  When  the  quantity  of  fluid  to  be  acted  upon  is  small, 
a  watch-glass,  or  a  piece  of  broken  flask  or  retort,  is  very 
convenient  as  a  receiver,  or  when  a  drop  only  of  the  fluid 
canbe  spared,  a  glass  plate  (1348)  will  support  it.   The  pole.s 
are  on  such  occasions  to  be  brought  towards  each  other  on 
opposite  sides  of  the  drop,  and  the  effect  minutely  examined 
and  noted. 


480 


VOLTAIC  ACTION — GASES  COLLECTED. 


1048.  With  a  view  of  increasing  the  acting  surfaces,  a 
platinum  capsule  may  be  used  to  receive  the  fluid  :  one  pole 
is  then  to  be  placed  in  contact  with  the  exterior  of  the  cap- 
sule, and  the  other  dipped  into  the  fluid  within.     Even  the 
surface  of  this  immersed  pole  may  be  extended  by  attaching 
a  piece  of  platinum  foil  to  it.     When  the  experiment  is  to 
be  continued  for  some  time  the  immersed  pole  may  be  sup- 
ported and  kept  from  contact  with  the  capsule,  by  putting  a 
little  piece  of  glass,  or  in  delicate  experiments,  a  fragment 
of  rock  crystal  into  the  solution,  allowing  the  wire  or  foil  to 
rest  upon  it. 

1049.  When  the  products  of  the  experiment  are  gaseous, . 
they  are  best  collected  by  the  use  of  tubes  similar  to  those 
already  described  (1046),  but  placed  in  an  inverted  position. 
If  such  a  tube  be  filled  with  a  saline  solution  for  instance, 
and  inverted  in  a  portion  of  the  same  solution  in  a  glass  or  other 
vessel,  not  of  metal,  then  by  dipping  the  negative  pole  of  a  bat- 
tery into  the  fluid  of  a  vessel,  and  connect- 

f  ing  the  wire  of  the  tube  with  the  positive 
pole,  action  will  take  place,  and  the  oxy- 
gen evolved  from  the  water  of  the  solution 
at  the  positive,  pole  will  be»  collected  in 
the  tube.  If,  in  place  of  one  such  tube, 
two  be  used,  both  standing  in  the  same 
vessel,  and  their  wires  connected  with  the 
poles  of  the  battery,  the  gases  evolved  at 
those  poles  are  collected  separately  in  the  tubes.  Or  if  both 
poles  be  introduced  into  the  same  tube  (1203),  then  the 
gases  are  collected  in  a  state  of  mixture. 

1050.  A  very  convenient  form  of  tube  for  the  collection 
and  examination  of  gases  evolved  in  small  experiments,  by 
either  one  pole  or  the  other,  is  shown  by  the  figure.     The 
tube  is  first  to  be  filled  with  the  solution  to  be  acted  upon, 
and  then  held  in  the  position  represented.     The  kind  of  gas 
collected  is  dependent  upon  the  pole  which  is  made  fast  to 
the  wire  at  a ;  the  other  is  to  be  inserted  at  b,  but  not  so  far 


VOLTAIC  DECOMPOSITION FLUIDS.  481 

as  to  allow  any  of  the  gas  from  it  to  pass  round 
the  bend  into  the  tube  ;  the  fluid  will  flow  out 
of  the  mouth  of  the  tube  as  the  gas  is  evolved 
at  the  pole  a.  When  the  vessel  is  sufficiently 
full  of  gas,  the  pole  6  is  to  be  removed,  and 
the  gas  examined  as  described  (950),  or  else, 
if  necessary,  transferred  and  examined  in  a 
more  minute  and  accurate  manner. 

1051.  In  the  arrangement  of  these  tubes,  and  in  all  de- 
compositions of  solutions,  it  is  better  to  use  platinum  foil  for 
the  termination  of  the  poles,  than  wire,  because  of  the  greater 
surface  of  contact  presented  by  such  a  pole  to  an  imper- 
fectly conducting  substance  (1038).     For  tubes,  therefore, 
which  have  platinum  wires  fused  into  them,  the  wire  should 
be  thick,  and  the  extremity,  for  a  length  nearly  equal  to 
that  of  the  tube,  flattened  out  into  foil ;  or  a  piece  of  plati- 
num foil  should  be  prepared  for  the  pole  inside  the  tube,  and 
be  made  fast  to  a  piece  of  wire,  either  by  close  contact  or 
gold  soldering,  before  the  latter  is  put  through  and  fused 
into  the  glass  (1201). 

1052.  In  all  arrangements  relative  to  the  decomposition 
of  water  or  aqueous  solutions  by  Voltaic  electricity,  the  young 
experimenter  should  keep  in  mind  the  effects  dependent  up- 
on variations  in  the  quantity  and  situation  of  the  fluid.     The 
fluid,  as  compared  with  the  metal  of  the  poles,  is  a  very  im- 
perfect conductor,  and  when  in  large  quantity,  offers  a  seri- 
ous obstacle  to  the  passage  of  electricity  of  the  low  intensity 
generated  by  the  Voltaic  pile :  and  yet  in  proportion  as  this 
passage  is  free  or  obstructed,  is  the  action  more  or  less  en- 
ergetic and  effectual.     The  necessity  for  bringing  the  poles 
near  to  each  other  has  therefore  been  insisted  upon  (1038), 
that  the  column  of  fluid  which  intervenes  between  them  may 
be  as  short  as  possible.     But  the  injurious  effect  which  oc- 
curs by  contracting  the  width  of  this  column  has  not  yet 
been  pointed  out. 

1053.  Suppose  that  the  poles  of  the  battery  are  two  plati- 
num wires,  and  that  they  have  been  immersed  in  a  saline  so- 
lution contained  in  a  glass,  and  placed  half  an  inch  apart ; 

3L 


482  OPPOSITE  POLES — PRECAUTIONS. 

gas  will  be  evolved,  and  a  certain  degree  of  action  will  be 
observed.  If  then  a  plate  of  mica  be  cut  into  such  a  form 
that  it  will  serve,  when  introduced  into  the  glass  vertically, 
to  divide  the  solution  into  two  parts,  each  containing  a  pole, 
and  if  a  notch  be  then  cut  in  the  mica  somewhat  wider  than 
the  immersed  wires,  and  of  equal  depth  with  them,  so  that 
when  returned  into  its  place  there  shall  be  a  passage  for  the 
solution  through  the  notch,  directly  between  the  two  poles 
and  of  equal  size  with  them,  or  even  rather  larger,  it  will 
still  be  found,  though  the  distance  between  the  poles  is  ex- 
actly the  same  as  when  no  mica  was  present,  that  their  ac- 
tion is  very  greatly  diminished.  This  effect  is  entirely  due 
to  the  contraction  of  the  thickness  of  the  connecting  column 
of  imperfectly-conducting  fluid;  and  if  the  mica  were  of  con- 
siderable thickness,  so  as  to  extend  the  notch  into  a  chan- 
nel of  half  or  three-quarters  of  an  inch  in  length,  then,  not- 
withstanding its  width  and  depth  would  be  the  same  as  be- 
fore, the  poles  would  hardly  exert  a  perceptible  power. 

1054.  All  this  may  be  easily  understood  by  considering 
that  what  the  fluid  wanted  in  conducting  power  had   been 
partly  made  up  by  its  mass,  and  that  by  diminishing  this 
mass,  the  channels  of  communication  had  been  in  a  great 
measure  closed;  but  this  is  very  often  forgotten  in  the  construc- 
tion of  apparatus,  and  in  conducting  of  experiments.     When 
two  poles  rise  through  the  bottom  of  a  glass,  they  may  act 
perfectly  well;  but  if  a  tube  of  glass  be  put  over  each,  to 
collect  the  gas  evolved,  the  circumstances  are  entirely  alter- 
ed.    There  are  very  few  parts  of  the  opposite  poles  that  are 
now  virtually  as  near  to  each  other  as  before,   and   those 
farthest  up  the  tubes  are  removed  to  a  distance  equal  to  the 
length  of  the  line  which  might  be  drawn  from  the  end  of  one 
pole  to  the  edge  of  the  tube  containing  it,  across,  to  the 
edge  of  the  other  tube,  and  upwards,  to  the  extremity  of  the 
pole  within  it.     Besides  this  increased  length,  the  thickness 
of  the  intervening  and  conducting  mass  of  fluid  is  very  much 
diminished  also,  being  equal  to  the  diameter  of  the   tubes 
only,  whereas,  before,  it  was   in  some  parts  equal   to  the 
diameter  of  the  glass  containing  solution  and  poles. 

1055.  A  similar  influence  is  exerted  to  a  great  extent  in 


VOLTAIC  BATTERY AQUEOUS  SOLUTIONS.       483 

experiments  where  the  poles  are  placed  in  different  vessels. 
These  vessels  require  to  be  connected  by  syphon  tubes  filled 
with  the  solution,  or  by  moistened  threads  of  cotton  or  ami- 
anthus. If  these  bridges  of  communication  be  small,  much 
power  will  be  wasted,  which  would  be  active  were  larger 
tubes  or  bundles  of  fibres  applied;  and  besides  making  them 
large,  they  should,  for  the  reasons  before  given,  also  be  as 
short  (1052)  as  the  other  circumstances  of  the  experiment 
will  allow.  Generally,  with  regard  to  the  fluid  intervening 
between  the  poles  of  the  battery,  the  endeavour  should  be  in 
all  cases  to  make  it  virtually  as  short,  and,  if  the  expression 
may  be  used,  as  massive  as  possible,  no  more  insulating  or 
retarding  matter  being  allowed  to  occupy  the  space  between 
the  poles  than  can  possibly  be  helped. 

1056.  Aqueous  solutions  generally  have  greater  conduct- 
ing power  than  pure  water,  and  advantage  may  be  taken  of 
this  circumstance  in  effecting  the  decomposition  of  water, 
and  even  of  some  other  bodies.     It  will  be  found  that  a  bat- 
tery which  will  scarcely  act  upon  water,  so  as  to  evolve  sen- 
sible portions  of  gas,  will  appear  to  acquire  twice  or  thrice 
its  former  power  by  putting  a  little  common  salt,  sulphate  of 
soda,  or  almost  any  saline  body,  into  the  water  under  decom- 
position.    A  small   quantity  only  is  required,  one  part  of  a 
saturated  solution  of  these  salts  to  six  or  eight  parts  of  water, 
producing  a  great  effect.     These  solutions  are  very  useful 
as  tests  of  the  existence  of  a  Voltaic  current,  capable  of 
effecting  chemical  changes.     When  substances  are  so  ar- 
ranged, that  it  is  supposed  an  electrical  current  of  some  in- 
tensity is  produced,  all  that  is  required  to  ascertain  the  cor- 
rectness of  the  opinion  is,  to  bring  a  wire  from  each  end  of 
the  arrangement,  and  immerse  their  extremities  in  a  drop  of 
a  weak  solution  of  salt;  if  gas  be  evolved,  it  is  a  proof  the 
opinion  is  well  founded.* 

1057.  The  plates  of  a  voltaic  battery  should  be  removed 

*  To  facilitate  the  galvanic  decomposition  of  water,  borax  is  preferred  by  Dr 
Hare  to  any  other  salt.  As  it  is  not  readily  affected  by  even  a  powerful  deflagra- 
tor,  it  does  not  very  sensibly  alter  the  transparency  or  colour  of  the  aqueous  so- 
lution.— ED. 


484      VOLTAIC  BATTERY  -  HARE?S  IMPROVEMENTS. 

from  the  action  of  the  charge  at  every  considerable  inter- 
mission of  the  experiments.  The  acid  rapidly  dissolves  and 
destroys  the  zinc  plates  during  the  time  it  is  in  contact  with 
them,  and  though  the  degree  of  action  may  not  be  of  such 
importance  as  to  justify  the  raising  of  the  plates  during  the 
cessation  of  experiments  for  a  minute  or  two,  or  even  for  a 
longer  time  in  particular  circumstances,  yet  they  should 
never  unnecessarily  be  left  to  the  action  of  the  charge,  when 
the  electricity  they  evolve  is  not  actively  employed  on  other 
bodies.  When  five  or  ten  minutes  intervene  between  one 
experiment  and  another,  it  is  worth  while  raising  the  plates 
of  a  battery  of  ten  or  twelve  troughs,  or  less,  from  the  cells; 
this  affords  the  additional  advantage  of  an  increase  of  action 
upon  their  re-immersion,  due  in  some  way  to  draining  or 
exposure  to  air.*  Instrument-makers  sometimes  hang  the 
plates  to  a  frame,  which  being  suspended  by  a  cord,  and 
connected  with  a  lever,  allows  the  whole  to  be  raised  or  de- 
pressed at  pleasure;  and  Dr  Hare  has  constructed  a  trough,f 
in  which  the  cells  being  formed  by  the  metallic  plates  (1028), 
the  charge  is  poured  on  and  off  at  pleasure,  by  a  quarter 
revolution  of  a  handle. 


*  "  The  passage  is  quoted  to  introduce  an  experiment  devised  by  Dr  Hare, 
which  shows  that  the  recovery  of  power  depends  solely  on  the  presence  of  oxy- 
gen or  other  electro-negative  substances.  For  if  we  place  a  voltaic  arrangement 
in  a  tubular  bell-glass,  and  apply  to  its  tubular  aperture  a  pipe  and  stop-cock, 
and  then  immerse  it  in  an  acidulous  solution,  the  bell-glass  will  be  filled  with 
hydrogen  gas.  No  recovery  ensues  from  repose  in  that  gas,  nor  when  nitrogen 
gas  is  substituted  ;  but  chlorine,  or  oxygen,  or  common  air  re-invigorates  the  in- 
strument, and  in  them  it  returns  to  its  ordinary  efficiency.  We  are  thus  enabled 
to  advance  a  step  towards  an  explanation  of  the  power  obtained  by  the  use  of 
acidulous  and  saline  solutions,  inasmuch  as  they  cause  the  readier  extrication  of 
oxygen  from  the  water  of  the  solution."  North  Amer.  Med.  and  Surg.  Journ. 
1829,  p.  355.—  ED. 

f  Philosophical  Magazine,  Ixiii.  241. 

t  Nothing  better  evinces  the  potency  of  the  prejudice  of  habit,  than  the  very 
casual  notice  of  Dr  Have's  improvement  on  the  discovery  of  Cruickshank.  Had 
so  acutely  practical  an  eye  as  that  of  Faraday,  once  rested  for  a  moment  on  the 
movements  and  effects  of  Hare's  apparatus,  we  should  have  had,  in  this  section, 
a  minute  description  both  of  its  construction  and  application.  It  fully  obviates 
every  difficulty,  for  the  avoidance  of  which,  in  the  usual  apparatus,  our  author 
goes  so  much  into  detail.  The  apparatus  of  Hare  consists  of  two  troughs,  at- 
tached to  each  other  lengthwise,  lip  to  lip,  at  right  angles,  so  that  when  one  is 
in  its  erect  position,  the  other  is  placed  horizontally,  an  order  which  may  be  re- 


VOLTAIC  BATTERY SIZE.  485 

1058,  Although  it  is  highly  advantageous  to  operate  with 
a  large  battery,  as  for  instance  of  100  pair  of  plates  four 
inches  square,  when  such  can  be  had,  and  when  the  object 
is  to  render  the  experiments  and  other  results  evident  at  a 
distance,  yet  such  a  power  is  by  no  means  always  necessary. 
Even  the  repetition  of  the  most  refined  and  admirable  ex- 
periments may  be  made  with  a  battery  no  way  comparable 
to  one  of  this  size,  if  the  object  of  the  experimenter  be  only 
to  satisfy  himself  or  those  close  to  him,  and  if  he  use  the 
precautions  as  to  contact,  vicinity,  &c.,  already  given.     A 
single  trough,  of  ten  pairs  of  plates  four  inches  square,  will 
suffice  to  repeat  nearly  all  the  experiments  that  have  yet 
been  made  on  the  decomposition  of  bodies  in  solution,  and 
all  those  relating  to  electro-magnetism.     Nor  is  it  essential 
that  a  greater  power  should  be  used  in  many  new  investiga- 
tions.    In  the  same  manner,  a  small  trough  with  40  or  50 
pairs  of  plates,  one  inch  square,  will  be  found  a  very  useful 
instrument  in  a  laboratory  not  affording  the  opportunity  of 
working  with  a  larger  arrangement  ;  and  the  habit  of  expe- 
rimenting with  small  apparatus,  and  on  a  minute  scale,  is 
highly  valuable  for  the  independence,  which  it  gives  to  the 
philosopher,  of  larger,  more  expensive,  and  consequently 
scarcer  instruments. 

1059.  Where  copper  and  zinc  in  sheets  can  be  obtained 
(and  there  is  now  scarcely  a  large  town  in  England  without 
them),  a  Voltaic  arrangement  may  easily  be  constructed. 
The  metals  are  to  be  cut  into  single  plates  of  equal  size,  two 
inches  square  for  instance,  arid  are  then  to  be  arranged  as  a 
pile  with  equal-sized  pieces  of  flannel  dipped  in  dilute  acid 
(1026)  in  the  order  zinc,  flannel,  copper;  zinc,  flannel,  cop- 
per; zinc,  flannel,  copper;  until  twelve  or  more  pairs  of  me- 

versed  by  a  quarter  revolution  of  a  handle  attached  to  an  axle,  which  is  nearly  in 
the  line  of  junction.  In  one  of  these  troughs  is  placed  the  metallic  plates,  the 
other  is  made  to  hold  the  solution.  A  quarter  of  a  revolution  precipitates  the 
liquid  instantaneously  on  the  plates,  and  a  reverse  movement  readily  throws  it  off 
again.  Thus  is  obtained  the  maximum  of  effect ;  while  even  during  the  shortest 
intervals,  the  acid  is  taken  off  with  convenience.  For  a  more  minute  account  of 
this,  in  this  country  the  most  common  because  the  most  useful  of  batteries,  the 
reader  is  referred  to  the  appendix  to  Dr  Hare's  Lectures  on  Electricity  and  Gal- 
vanism.— ED. 


486  VOLTAIC  ARRANGEMENTS. 

tallic  plates  have  thus  been  put  together.  Such  an  arrange- 
ment should  be  made  in  a  plate,  that  any  acid  exuding  from 
it  may  be  caught  and  retained.  The  surfaces  of  the  con- 
tiguous metallic  plates  should  be  clean,  that  the  contact 
between  them  may  be  good.  To  ensure  this,  it  is  convenient 
to  solder  the  plates  together  at  their  edges  into  pairs;  each 
comprising  a  zinc  and  a  copper  plate.  On  building  these 
up  with  the  intervening  flannels,  the  order  will  be  copper, 
zinc,  flannel ;  copper,  zinc,  flannel ;  copper,  zinc,  &c.  The 
wires,  which,  when  attached  to  the  top  and  bottom  of  this 
pile,  serve  as  its  poles,  should  be  clean  and  in  good  contact 
with  the  end  plates,  and  then  a  pile  of  twenty  of  these  pairs 
will  be  found  to  have  very  considerable  power,  and  be 
competent  to  the  performance  of  a  great  number  of  experi- 
ments. 

1060.  The  nature  of  the  poles  of  an  ordinary  battery  may 
be  determined  by  inspection  of  any  one  of  the  pairs  of  me- 
tallic plates  employed  in  its  construction.     The  end  of  the 
battery  on  the  zinc  side  of  the  pair  examined  is  the  positive 
pole ;  the  end  on  the  copper  side  of  the  same  pair  is  the  ne- 
gative pole.     This  holds  good  wherever  the  pair  may  be  in 
the  battery,  or  however  far  the  ends  may  be  removed. 

1061.  Electro-magnetic,  and  many  other  experiments  re- 
lative to  the  transmission  of  electricity  through  good  con- 
ductors, such  as  the  metals,  and  the  effects  produced  there- 
by, often  require  for  their  performance  Voltaic  arrangements, 
consisting  of  a  few  large  plates  rather  than  many  small  ones. 
It  is  easy  to  arrange  the  ordinary  troughs,  consisting  of  ten 
pairs  of  plates  four  inches  square,  so  as  to  produce  intensity 
or  quantity  at  pleasure.     Thus  if  four  of  these  troughs  were 
to  be  used  for  chemical  experiments,  it  would  be  best  to 
place  them  end  to  end  in  their  proper  order,  so  as  to  forma 
battery  of  forty  pairs  of  plates  four  inches  square,  connect- 
ing them  if  necessary  in  the  manner  described  (1034):    but 
if  large  plates  and  few  in  number  be  more  advantageous, 
then  these  four  troughs  may  be  arranged  so  as  to  form  a 
battery  equivalent  to  one  of  ten  pair  of  plates  eight  inches 
square.     For  this  purpose  they  must  be  placed  with  their 


ELECTRO-MAGNETIC  EXPERIMENTS.  487 

sides  together,  their  similar  ends 
being  in  the  same  direction;  and 
they  should  be  connected  by  two 
thick  pieces  of  copper  wire,  bent 
according  to  the  figure,  in  such  a  manner  that  the  lower 
angles  of  one  piece  will  enter  the  four  terminal  cells  at  one 
end  of  the  battery;  this,  if  in  perfect  contact  with  the  plates 
(1034),  will  connect  them  together.  The  second  piece  will 
perform  the  same  office  at  the  other  ends  of  the  troughs, 
and  the  projecting  terminations  of  these  wires  are  to  be  used 
as  the  poles  of  the  battery. 

1062.  A  single  pair  of  plates  is  sufficient  for  the  perform- 
ance of  nearly  all  electro-magnetic  experiments,  and  a  com- 
bination of  this  kind  may  be  constructed  with  great  facility 
by  those  who  possess  a  piece  of  plate  zinc  and  a  piece  of  plate 
copper.    They  require  merely  to  be  put  neareachother  in  a  jar 
or  vessel  of  dilute  acid,  and  connected  by  a  wire.     The  plates 
may  be  conveniently  tied  together  with  a  couple  of  pieces  of 
glass  rod  or  tobacco-pipe  between  them,  to  prevent  metallic 
contact.    A  thick  wire  a  few  inches  in  length  should  be  attach- 
ed to  each  plate,  to  act  virtually  as  the  poles  (though  they  are 
not  really  poles  according  to  the  usual  acceptation  of  that  word 
in  Voltaic  electricity),  and  these  wires  or  poles  should  be 
connected  by  the  experimental  wire,  which,  though  thinner 
than  the  former,  should  not  be  unnecessarily  long.     This  ar- 
rangement has  been  described  as  formed  of  flat  pieces  of 
zinc  and  copper  plate,  but  any  shape  may  be  given  to  them, 
so  that  their  relative  position  is  the  same:  they  may  be  coil- 
ed ;  or  even  a  copper  vessel  may  be  used  instead  of  a  copper 
plate,  and  then  the  jar  for  containing  the  acid  may  be  dis- 
pensed with  altogether. 

1063.  The  double  copper  arrangement  described  by  Dr 
Wollaston  is  excellent  for  ordinary  experiments,  and  may 
easily  be  constructed.    It  consists  of  a  plate  of  zinc  surround- 
ed on  both  sides  by  a  plate  of  copper,  so  that  a  surface  of 
the  latter  is  brought  into  opposition  with  both  surfaces  of 
the  zinc.     This  arrangement  when  immersed  in  acid  is  very 
powerful ;  a  zinc  plate  of  less  than  an  inch  square  being  able 
to  effect  the  ignition  of  fine  platinum  wire,  the  deflection  of 


488  DR  WOLLASTON'S  ARRANGEMENT. 

the  magnetic  needle,  and  most  of  the  electro-magnetic  ex- 
periments. 

1064.  It  is  necessary  the  student  should  be  informed  that 
instruments  consisting  of  a  single  pair  of  plates  have  no  che- 
mical action.5* 

1065.  Dr  Wollaston's  beautiful  Voltaic  arrangement  for 
the  precipitation  (523)  of  certain  metals,  is  so  instructive,  and 
in  many  cases  so  useful,  that  it  must  not  be  here  omitted. 
It  was  devised  for  the  separation  of  cadmium  from  the  so- 
lution of  the  ore  or  metal  under  examination,  after  all  that 
could  be  precipitated  by  zinc  alone  (522)  had  been  thrown 
down.     The  solution  rendered  slightly  acid  was  put  into  a 
platinum  crucible,  and  a  rod  of  zinc  also  introduced,  so  as  to 
rest  on  the  bottom  and  at  the  edge  of  the  vessel :  this  formed 
a  Voltaic  combination  with  the  platinum  and  the  fluid ;  elec- 
tro-chemical action  took  place,  and  the  cadmium  was  pre- 
cipitated on  the  platinum,  which  was  the  negative  part  of 
the  arrangement.     When  the  separation  of  the  cadmium  had 
been  completed,  the  zinc  was  removed,  the  solution  poured 
out,  the  crucible  with  the  cadmium  adhering  to  it  washed 
with  distilled  water ;  then  a  little  nitric  acid  being  used,  it 
dissolved  the  latter  metal  without  causing  any  injury  to  the 
platinum. 

1066.  A  very  usual   problem  which  the  chemist  has  to 
solve  is,  whether  a  substance  be  a  conductor  of  electricity  or 
not,  or  what  is  the  degree  of  conducting  power  which  it 
possesses  with  regard  to  electricity.     Whether  it  conduct 
like  a  metal  or  not  may  be  ascertained  in  the  following  man- 
ner.    If  a  piece  of  zinc  and  a  piece  of  silver  be  placed  one 
above  and  the  other  below  the  tongue,  and  the  edges  be 
then  brought  into  contact,  a  peculiar  taste  will  be  perceived 
at  the  moment,  which  will  be  repeated  every  time  the  contact 
is  broken  and  renewed.     If,  instead  of  bringing  the  zinc  and 
silver  in  direct  contact,  a  piece  of  metal,  as  a  wire,  inter- 
vene, the  taste  will  still  be  perceived ;  but  if  the  interposed 

*  The  author  cannot  be  supposed  to  mean  that  the  surfaces  or  poles  of  a  sin- 
gle pair  suffer  no  modification  of  attractive  and  repulsive  power.  That  is  a  ne- 
cessary consequence  of  their  position. — Ei>. 


CONDUCTING  POWER EXAMINED.  489 

substance  be  a  body  not  metallic,  or  one  of  those  numerous 
substances  which,  though  they  conduct  electricity,  are  less 
efficient  than  the  metals,  a  piece  of  wet  paper  for  instance, 
a  piece  of  starch,  or  even  a  piece  of  galena,  then  no  taste 
will  be  occasioned.  The  experiment  should  therefore  be 
made  first  with  the  zinc  and  silver,  and  having  succeeded, 
the  substance  to  be  tried  should  be  placed  between  the  two 
metals,  and  the  attempt  repeated;  the  production  or  non-pro- 
duction of  taste  will  immediately  indicate  whether  it  con- 
ducts electricity  or  not.  All  the  pure  metallic  bodies,  and 
all  combinations  of  them  with  each  other,  conduct  electric- 
ity so  well  as  to  occasion  the  taste ;  but  as  yet  no  other 
substance  has  been  ascertained  to  do  so,  nor  even  any  of  the 
definite  compounds  of  metals  with  other  substances,  as  sul- 
phur or  oxygen.  Dr  Wollaston's  method  of  preventing  ac- 
cidental contact  of  the  zinc  and  silver  on  one  side  of  the  sub- 
stance to  be  tried  is  very  useful  *  :  it  is  to  cut  a  hole  in  a 
piece  of  card,  and  lay  the  doubtful  body  in  this  hole  between 
the  other  metals;  its  contact  and  retention  in  its  place  is  se- 
cured, and  the  accidental  contact  of  the  known  metals  per- 
fectly prevented. 

1067.  Evidences  of  the  conducting  power  of  solutions  and 
transparent  fluids  are  of  the  following  kind.     If  on  placing 
a  small  portion  between  the  Voltaic  pojes,  gas  be  evolved, 
or  metals  or  other  substances  separated,  or  any  change  effect- 
ed which  would  not  have  taken  place  by  mere  contact  of 
the  liquid  and  the  metal  of  the  pole  distinct  from  the  battery, 
such  action  is  a  proof  that  a  current  of  electricity  is  passing, 
and  consequently  that  the  fluid  is  a  conductor;  and  the  en- 
ergy of  the  action  is  to  a  certain  degree  an  indication  of  the 
degree  of  conducting  power.     A  small  Voltaic  battery  is 
sufficient  for  this  purpose. 

1068.  It  is,  however,  possible,  though  not  usual,  that  no 
apparent  change  may  take  place,  notwithstanding  the  body 
is  a  conductor,  equally  good  with  those  fluids  which  suffer 
decomposition  ;  this  is  the  case  with  fluid  chlorine.     In  such 
instances,  besides  the  portion  of  fluid   to  be  tested,  there 
should  be  in  another  vessel  a  portion  of  a  solution  of  salt; 

*  Philosophical  Transactions,  1823,  p.  20. 
3M 


490  CONDUCTING  POWER — TESTS. 

one  of  these  should  be  connected  with  one  pole  of  the  bat- 
tery, the  other  with  the  other  pole,  and  a  piece  of  platinum 
wire  should  be  bent  so  as  to  dip  into  both  portions  of  fluid, 
and  its  ends  should  be  brought  near  to  the  ends  of  the  poles 
immersed.  There  are  thus  two  portions  of  matter  ready  to 
be  decomposed  by  the  electric  current :  if  the  decomposition 
is  seen  by  the  liberation  of  gas  to  proceed  in  the  solution  of 
salt,  it  is  a  proof  that  the  other  fluid  is  a  conductor  of  elec- 
tricity sufficient  for  this  purpose :  if  no  decomposition  take 
place  in  the  solution,  then  the  other  fluid  will  not  permit 
Voltaic  electricity  of  this  intensity  to  pass,  and  is  in  that 
respect  a  non-conductor. 

1069.  The  same  kind  of  trial  serves  for  such  solid  bodies 
as  are  not  comparable  to  metals  with  regard  to  this  property, 
they  being  then  substituted  for  the  liquid  in  this  experiment, 
and  the  solution  of  salt  acting  the  part  of  a  test  as  before. 
It  will  in  this  way  be  found  that  several  of  the  native  and  ar- 
tificial compounds  of  the  metals  and  other  bodies  conduct 
electricity,  though  by  no  means  with  a  readiness  sufficient  to 
answer  the  test  of  taste  first  proposed  (1066). 

1070.  Again,  there   are   very  many   substances   which, 
though  so  inferior  in  conducting  power  as  to  appear  perfect 
insulators  by  these  modes  of  trial,  will  yet  show  many  de- 
grees of  it  by  more  powerful  tests,  that  is,  by  electricity  of 
higher  intensities.    These  are  generally  classed  amongst  very 
bad  conductors,  and  are  most  readily  examined  perhaps  by 
the  gold  leaf  electrometer  (1012).     If  the  electrometer  be 
diverged,  and  its  cap  then  touched  by  any  substance  held  in 
the  fingers,  or  at  the  end  of  a  wire,  it  will  be  discharged,  and 
the  leaves  collapsed  with  more  or  less  rapidity,  according  to 
the  conducting  power  of  the  substance.     If  the  leaves  retain 
their  first  divergence,  it  is  a  proof  of  the  entire  absence  of 
conducting  power,  as  far  as  our  tests  usefully  extend.     For 
the  application  of  this  method  to  a  liquid,  the  latter  should 
be  placed  in  a  convenient  vessel,  a  capsule  or  tube  for  in- 
stance, connected  by  a  wire  or  the  hand  with  the  earth,  and 
then  a  piece  of  bent  wire,  well  ineulated  by  a  stick  of  sealing- 
wax  or  gum  lac,  is  to  be  made  to  touch  the  cap  of  the  elec- 
trometer by  one  end,  and  the  surface  of  the  fluid  by  the  other. 
If  the  leaves  collapse  entirely,  it  is  a  proof  that  the  fluid 
conducts  electricity. 


ROUSSEAU'S  TEST — GAS  IN  CIRCUIT.  491 

1071.  M.  Rousseau  *  has  devised  a  very  ingenious  varia- 
tion of  this  test.     He  brings  one  end  of  a  dry  electric  col- 
umn into  contact  with  the  cap  of  the  electrometer,  and  re- 
tains it  there.     This  occasions  a  divergence  of  the  leaves  to 
an  extent  dependent  upon  the  power  of  the  pole.     He  then 
connects  the  cap  of  the  electrometer  with  the  earth  through 
a  portion  of  the  fluid  or  substance  to  be  tried,  and  observes 
to  what  extent  this  reduces  the  previous  divergence  of  the 
leaves.     If  the  divergence  be  entirely  destroyed,  it  shews  a 
conducting  power  which  is  considerable,  compared  to  that 
of  most  bodies  which  may  be  tried  by  this  method;  if  but 
slightly  diminished,  it  indicates  but  little  conducting  power. 
Decided  distinctions  may  be  established  between  even  the 
different  oils  by  this  method. 

1072.  Although  the  great  use  of  the  Voltaic  pile  is  to  ef- 
fect chemical  change  by  means  of  the  peculiar  power  of  its 
poles,  it  is  often  otherwise  applicable.     When  the  discharge 
of  a  powerful    battery  is  made  through  air    between  two 
pieces  of  charcoal,  the  heat  is  very  intense,  and  is  extended 
over  a  larger  space  than  when  the  discharge  takes  place  be- 
tween two  pieces  of  metal.     To  this  temperature  any  gas 
may  be  subjected,  in  which  the  discharge  is  made,  and  the  ef- 
fects upon  it  may  be  observed.     Carburetted  or  sulphuretted 
hydrogen  are  thus  decomposed.     Other  gases  examined  in 
the  same  manner  would  probably  present  peculiar  phenomena. 

1073.  By  transmitting  the  Voltaic  current  through  thin 
wires,  they  are  heated,  ignited,  and  fused.     This  effect  sup- 
plies a  means  of  conveying,  or  rather  of  producing  and  ap- 
plying heat  in  situations  in  which  it  could  not  otherwise  be 
excited,  and  thus  facilitates  certain   refined   experiments. 
Substances  having  wires  passed  through  them  may  be  placed 
within  globes  under  water,  or  in    remote  situations,  and 
then  be  heated,  ignited,  and  exploded :  eudiometers  have 
been  constructed  in  which  a  fine  wire  passing  across  the  cav- 
ity has  been  ignited  by  a  Voltaic  battery,  and  thus  used  to 
inflame  the  included  mixture  of  gases.f 

*  Annales  de  Chimie,  xxv.  373. 

t  Hare's  Eudiometer  (sliding-rod  hydroxygen  Eudiometer)  is  constructed  so  as 
to  admit  of  the  inflammation  of  the  mixed  gases  by  galvanic  ignition    Our  limits 


492 

1074.  The  insulation  of  substances  is  frequently  required 
in  electro-chemical  investigation,  and  numerous  methods 
must  be  resorted  to,  according  to  the  circumstances  of  ex- 
periments. When  an  insulating  plane  is  required,  a  plate  of 
mica  is  the  best  substance  for  the  purpose,  then  a  plate  of 
resin  or  wax,  or,  in  their  absence,  a  plate  of  warm  glass.  In 
all  similar  insulations,  the  substance  to  be  supported  should 
be  placed  so  far  from  the  edges  of  the  insulating  planes,  as  to 
be  independent  in  its  electrical  state  of  the  neighbouring  bo- 
dies; and  it  is  also  convenient  to  support  the  insulating  planes 
themselves  upon  a  glass  jar  or  other  vessel,  in  those  cases  at 
least  where  the  state  and  degree  of  electricity  of  the  insula- 
ted substance  is  to  be  minutely  examined.  For,  if  the  insu- 
lating plane  lie  on  a  table  or  other  conducting  body,  it  al- 
lows of  induction  through  it;  and  thus,  without  any  actual 
communication,  permits  the  electricity  of  the  body  upon  it 

do  not  permit  a  full  description  of  this  beautiful  specimen  of  philosophical  inven- 
tion, for   which   the  reader  is  referred  to  Hare's  Compendium,  p.  121  et  seq- 


W      W 

The  essential  parts  of  this  instrument  are,  1.  A  cavity  extending  from  A  to  Hof 
which  G  is  glass  and  the  remainder  metal.  At  A  is  seen  a  capillary  orifice  opened 
or  closed  at  pleasure,  by  a  lever  and  spring,  which  Dr  Hare  sometimes  assists  by 
a  gallows-screw.  2.  At  H,  is  another  aperture,  through  which  passes  easily  a 
graduated  rod  surrounded  at  that  point  by  a  collar  of  leather,  so  as  to  make 
the  passage  air-tight.  3.  Through  the  metallic  bottom  of  the  socket  S,  pass  two 
wires  of  brass,  surmounted  by  a  small  platinum  arch.  One  of  these  wires  is 
wrapped,  so  as  to  prevent  its  contact  with  the  metallic  bottom. 

By  means  of  the  sliding- rod,  the  Eudiometer  is  easily  filled  with  wafer,  and  is 
prepared  for  use  by  afterwards  thrusting  the  rod  into  the  cavity  up  to  the  handle. 
In  examining  the  atmosphere  100  measures,  or  degrees  of  the  rod  being  drawn  out, 


INSULATION — HARE'S  CALORIMOTOR.  493 

to  be  influenced  in  an  uncertain  and  variable  manner.  For 
the  same  reason  when  a  body  is  insulated  for  minute  and  deli- 
cate examination,  no  projecting  mass  of  conducting  matter 
should  be  allowed  to  exist  in  its  immediate  neighbourhood, 
because  of  the  influence  which  will  then  be  exerted  upon  it 
by  induction  through  the  air. 

1075.  When  glass  pillars,  or  stools  with  glass  legs,  or  a 
common  glass  (36S),  is  used  for  insulation,  they  should  al- 
ways be  well  warmed  and  dried;  and  glass  apparatus,  which  is 
constantly  appropriated  to  this  use,  should  be  varnished  with 

that  quantity  of  air  will  enter  at  A,  and,  by  placing  the  apex  under  an  inverted 
glass  holding  hydrogen  gas,  an  equal  retraction  of  the  rod  will  add  to  the  air  100 
measures  of  hydrogen.  The  lever  being  applied  closely  at  A,  and  the  gases  well 
mixed;  the  mixture  is  ignited  by  applying  the  wires  W  W  to  Hare's  Calorimotor. 


The  combustion  lessens  the  quantity  of  gaseous  matter,  and  produces  a  rare- 
fied state,  so  that  when  the  instrument  is  opened  under  water,  as  much  water  en- 
ters as  is  equal  in  bulk  to  the  gases  destroyed.  The  ascertainment  of  that  quan- 
tity is  accomplished  by  pushing  inwards  the  rod,  until  all  the  remaining  gas  is 
excluded,  and  the  cavity  is  full  of  water  only.  The  portion  of  the  rod  left  with- 
out represents  the  quantity  of  water  which  entered  after  the  explosion,  and  of 
course  the  quantity  of  the  gases  consumed.  One.  third  of  the  quantity  is  the 
oxygen  contained  in  100  measures  of  air.  So  convenient  is  this  instrument, 
that  the  analysis  may  be  completed  at  least  twice,  in  the  space  of  time  occupied 
in  its  description*.— ED. 


*  Both  the  Eudiometer  and  Calorimotor  may  be  had  of  Alva  Mason,  Green- 
leaf's  court,  Philadelphia;  who  can  furnish  most  of  the  instruments  described 
in  this  volume. — ED. 


494  INSULATION — BY  GLASS — RESINS — SILK. 

a  solution  of  sealing-wax  in  strong  alcohol.  Ordinary  glass 
has  such  an  attraction  for  water,  that  at  common  tempera- 
tures its  exposed  surface  is  constantly  moistened  to  a  certain 
degree;  in  consequence  of  which  it  becomes  a  conductor  of 
electricity  of  such  tensions  as  are  sensible  by  the  gold  leaf 
electrometer,  and  is  therefore  a  bad  insulator.  A  glass  rod 
well  warmed  and  rubbed,  and  then  left  exposed  to  the  air  to 
cool,  will  be  found,  after  a  few  hours,  capable  of  discharging 
a  gold  leaf  electrometer,  solely  by  the  film  of  moisture  on  its 
surface;  for  if  glass  be  examined  in  an  unexceptionable  man- 
ner, it  has  not  itself  those  conducting  powers  at  common 
temperatures.  Resins  are  very  superior  to  glass  in  this  re- 
spect, and  hence  the  use  of  the  varnish  recommended. 

1076.  In  experiments  upon  the  manufacture  of  glass  for 
optical  purposes,  I  have  found,  that  with  such  as  contained  no 
alkali,  but  consisted  of  silica,  boracic  acid,  and  oxide  of  lead, 
the  insulation  was  so  perfect  as  to  equal  if  not  surpass  that 
of  lac  resin  *.     This  glass  is  not  at  present  in  use,  but  may 
hereafter,  because  of  this  and  other  properties,  be  very  use- 
ful in  electrical  investigations. 

1077.  When  a  small  mass  of  solid  matter  is  to  be  insulat- 
ed by  a  handle,  it  may  be  effected  by  a  piece  of  white  silk 
thread  dipped  into  and  stiffened  by  melted  gum-lac,  or  by  a 
rod  or  thread  of  the  same  resin.    This  substance  is  easily 
melted  and  drawn  out  into  threads  of  different  diameters, 
and  surpasses  every  other  in  insulating  power  at  common 
temperatures. 

1 078.  If  a  body  is  to  have  a  suspensive  insulation,  then  silk 
thread  or  cord  may  be  advantageously  resorted  to,  but  in 
such  cases  white  silk  should  be  used.     Black  silk  frequently 
conducts  as  well  as  a  moistened  thread,  and  coloured  silks 
are  often  very  inferior  in  this  respect  to  white,  in  consequence 
of  the  dye  stuff  they  contain  conferring  a  certain  degree  of 
conducting  power. 

1079.  There  are  no  particular  instructions  required  in  re- 
lation to  electro-magnetic  experiments  beyond  those  which 
have  already  been  given.     The  contacts  should  be  carefully 

*  Philosophical  Transactions,  1830,  p.  49. 


LUTES CEMENTS THEIR  NATURE.          495 

attended  to ;  the  part  of  the  connecting  wire  which  is  experi- 
mented with  removed  and  preserved  as  far  as  it  can  be  from 
other  parts  of  the  wire,  and  from  the  battery,  that  the  needle 
or  apparatus  experimented  with  may  be  subject  to  no  other 
influence  than  that  of  the  wire  alone.  The  magnets  used 
should  be  strong,  their  magnetic  poles  well  determined,  and 
not  irregularly  diffused  over  the  steel  of  which  the  magnets 
consist.  The  points  of  support  for  the  magnetic  needles 
should  be  attended  to  (1390, 1398),  and  the  needles  should  be 
in  an  active  state. 


SECTION  XVIII. 

LUTES— CEMENTS. 

1080.  IT  is   intended  in  this  section  to  comprise  such  an 
account  of  Lutes  and  Cements,  with  the  methods  of  apply- 
ing them,  as  shall  enable  the  student  to  select  that  which  is 
most  fitted  for  his  particular  purpose,  and  make  it  answer  the 
required  end  with  the  greatest  success. 

1081.  Lutes  are  soft  adhesive  mixtures,  principally  earthy, 
used  either  for  closing  apertures  existing  at  the  junction  of 
different  pieces  of  apparatus,  or  for  coating  the  exterior  of 
vessels  which  are  to  be  subjected  to  a  high  temperature;  the 
latter  application  being  either  for  the  purpose  of  strengthen- 
ing them,  and  preventing  their  fracture  (489),  or  for  repair- 
ing a  fracture,  or  to  prevent  the  contact  of  the  air.     There  are 
but  few  lutes  used  for  the  latter  purpose;  and  the  success  of 
the  operation,  which  is  usually  called  coating,  is  generally 
more  dependent  upon  the  manner  in  which  it  is  performed, 
than  upon  the  lute  itself.     But  those  which  have  been  ap- 
plied for  the  purpose  of  rendering  junctions  tight,  are  very 
numerous,  in  consequence  of  the  variety  of  vapours  which  re- 
quire to  be  confined,  and  the  difference  of  temperature  to 
which  they   are  occasionally  subjected.     The  term  luting 
has  occasionally  been  confined  to  this  application. 


496  LUTES — COATING  A  VESSEL. 

1082.  The  lutes  which  are  used  for  junctions  pass  by  de- 
grees into  cements,  the  two  sets  of  bodies,  if  considered  as 
distinct,  being  frequently  convertible  in  their  uses  into  each 
other.     For  this  reason,  both  will   be  comprised  in  this  sec- 
tion, and  also  such  other  applications  of  these  substances  as 
may  be  useful  in  the  laboratory. 

1083.  The  vessels  which  require  coating  are  generally  re- 
torts, flasks  and  tubes,  sometimes  crucibles  and  other  vessels. 
Occasionally  the  temperature  to  be  sustained  is  very  high,  at 
other  times  a  high  red  heat  only  is  to  be  provided  against; 
and  in  other  instances  the  coating  is  rather  for  the  purpose 
of  rendering  vessels  impervious  to  air  (491,  492),  than  to  de- 
fend them  from,  or  strengthen  them  in  the  fire. 

1084.  When  the  coating  must  sustain  a  very  high  tempera- 
ture, as  in  the  preparation  of  potassium  by  the  gun-barrel,  or 
in  the  attachment  of  a  crucible  to  its  support,  it  should  be 
made  of  the  best  Stourbridge  clay,*  no  other  earthy  sub- 
stance found  in  this  country  being  so  capable  of  resisting  fire 
without  softening  or  fusion. 

1085.  The  lute  is  to  be  made  into  a  paste,  varying  in  thick- 
ness or  composition  according  to  the  opinion  of  the  experi- 
menter, as  will  immediately  be    pointed  out.      The  paste 
should  be  beaten  until  it  is  perfectly  ductile  and  uniform,  and 
a  portion  should  then  be  flattened  into  a  cake  of  the  required 
thickness,  and  of  such  size  as  shall  be  most  manageable  with 
the  vessel  to  be  coated.     If  the  vessel  be  a  retort  or  a  flask,  it 
should  be  placed  in  the  middle  of  the  cake,  and  the  edges  of 
the  latter  raised  on  all  sides,  and  gradually  moulded  and  ap- 
plied to  the  glass:  if  it  be  a  tube,  it  should  be  laid  upon  one 
edge  of  the  plate,  and  then  applied  by  slowly  rolling  the  tube 
forward.     In  all  cases  the  surface  to  be  coated  should  be  rub- 
bed over  with  a  piece  of  the  lute  dipped  in  water,  for  the  pur- 
pose of  slightly  moistening  and  leaving  a  little  of  the  earth 
upon  it;  and  if  any  part  of  the  surface  becomes  dry  before 
the  lute  is  applied,  it  should  be  moistened.     The  lute  should 
be  pressed  and  rubbed  down  upon  the  glass  successively, 

*  Stourbridge-clay,  fire-clay,  or  indurated  clay,  is  commonly  of  a  bluish-gray 
colour,  resists  the  action  of  the  nail  when  first  dug  up,  but  falls  to  pieces  by  ex- 
posure to  air  and  moisture,  and  becomes  plastic.— ED. 


COATING  OP  A  VESSEL.  497 

from  the  part  where  the  contact  was  first  made  to  the  edges, 
until  all  air  bubbles  are  excluded,  and  an  intimate  adhesion 
effected.  If  the  lute  be  inconsiderately  and  carelessly  press- 
ed upon  small  surfaces,  as  by  the  thumb  or  a  finger,  it  will 
frequently  extend  laterally,  become  of  greater  dimension 
than  the  vessel  beneath,  and  consequently  will  form  a  kind  of 
bag  about  it,  with  air  intervening.  This  must  be  avoided  by 
moderating  the  pressure,  making  it  more  general,  and  ap- 
plying it  so  that  the  coat  rather  tends  to  thicken  than  other- 
wise ;  and  if  an  air  bubble  should  accidentally  be  formed,  the 
endeavour  should  not  be  to  expel  the  air  by  passing  it  along 
between  the  coat  and  the  vessel  to  the  edge  of  the  luting, 
but  by  a  hole  to  be  pricked  with  a  pin  through  the  luting 
over  the  bulb. 

1086.  When  one  cake  of  lute  has  been  applied,  and  is  not 
large  enough  to  cover  the  whole  required  surface,  another 
must  be  adapted  in  a  similar  manner.     Particular  care  must 
be  taken  in  joining  the  edges;  for  which  purpose  it  is  better 
to  make  them  thin  by  pressure,  and  also  somewhat  irregular 
in  form,  and  if  at  all  dry  they  should  be  moistened  with  a 
little  soft  lute.     Afterwards  they  should  be  well  pressed  to- 
gether, that  the  adhesion  may  be  as  perfect  there  as  in  every 
other  part. 

1087.  If  from  irregularity  in  the  form  of  the  vessel  coated, 
as  for  example  about  the  neck  of  a  retort,  the  thickness  of 
lute,  after  a  little  pressure  and  moulding,  should  be  somewhat 
uncertain,  it  may  easily  be  ascertained  by  passing  a  needle 
through  it,  and  observing  the  depth  to  which  it  penetrates. 
The  minute  hole  thus  formed  is  rarely  of  consequence,  and 
may  be  obliterated  by  a  little  pressure  towards  it  upon  the 
lute  in  the  immediate  vicinity.     The  general  thickness  may 
be  from  one  fourth  to  one  third  of  an  inch. 

1088.  Being  thus  luted,  the  vessels  are  afterwards  to  be 
placed  in  a  warm  situation  over  the  sand-bath,  or  near  the 
ash-pit  of  the  furnace,  or  in  the  sun's  rays.     They  should  not 
be  allowed  to  dry  rapidly  or  irregularly,  and  should  be  moved 
now  and  then  to  change  their  positions.     When  dry  they 
should  never  again  be  allowed  to  become  damp. 

1089.  With  respect  to  the  best  state  of  the  lute,  there  is 
3N 


498  LUTES THEIR  STATE. 

considerable  variety  of  opinion  and  practice.  The  object  is  to 
diminish  the  contraction  which  the  moist  clay  undergoes,  first 
in  drying  in  the  air,  and  afterwards  when  heated  in  the  fire. 
By  some,  the  clay  is  beaten  into  a  very  fine  and  uniform  paste 
with  water,  just  so  much  of  the  latter  being  added  as  to  make 
the  mass  ductile  and  capable  of  application  ;  it  is  then  applied 
to  the  surface  of  the  retort  or  tube,  in  the  manner  described, 
until  it  forms  a  coat  upon  its  surface,  from  the  fourth  to  the 
half  of  an  inch  in  thickness,  according  to  the  size  of  the  ves- 
sel, and  the  degree  of  strength  required  in  the  coating.  Du- 
ring the  drying  this  coating  will  crack;  these  cracks  are  to 
be  carefully  filled  up  with  a  portion  of  the  same  lute,  again 
dried,  and  again  repaired  if  necessary,  until  the  exterior  ap- 
pears sound  and  perfect. 

1090.  Others  apply  their  lute  in  a  much  softer  and  more 
ductile  state.     This  facilitates  the  operation,  but  upon  dry- 
ing, the  cracks  are  generally  larger,  and  though  these  may 
be  filled  up,  and  the  whole  exterior  made  to  appear  sound 
and  perfect,  it  will  be  evident  that  the  separation  of  the  coat- 
ing from  the  vessel,  which  must  necessarily  occur  during  the 
contraction  of  the  clay,  must  proceed  to  a  greater  extent 
with  the  latter  kind  of  luting  than  the  former. 

1091.  When  vessels  thus  luted  are  introduced  into  the 
fire,  and  highly  heated,  further  contraction  of  the  aluminous 
coating  takes  place.     If  the  vessel  itself  be  iron  or  earthen- 
ware, it  does  not  give  way  to  the  diminished  bulk  of  the 
coating,  but  actually  expands  beneath  it,  and  thus  new  di- 
visions in  the  coating  are  produced  ;  the  former  partial  ad- 
hesion of  it  to  the  vessel  is  much  diminished,  and  its  tenden- 
cy to  separate  and  fall  off  in  fragments  is  much  increased. 
When  the  coated  vessel  is  glass,  this  does  not  happen  to  such 
an  extent,  for  the  heated  glass  yields,  and  gives  way  to  the 
contraction  of  the  coating,  which,  if  it  retain  its  unity  and 
form  until  the  glass  has  softened,  actually  becomes  an  earth- 
enware vessel  lined  with  vitreous  matter  (489). 

1092.  To  prevent  cracking  during  desiccation,  and  the 
consequent  separation  of  the  coat  from  the  vessel,  some  chem- 
ists recommend  the  introduction  of  fibrous  substances  into 
the  lute,  so  as  mechanically  to   increase  the  tenacity  of  its 


LUTES — COATED  VESSELS— CRACKING.  499 

parts.  Horse  dung,  chopped  hay  and  straw,  horse  and  cow 
hair,  and  tow  cut  short,  are  amongst  the  number.  When 
they  are  used  they  should  be  added  in  small  quantity,  and  it 
is  generally  necessary  to  add  more  water  than  with  simple 
lute,  and  employ  more  labour  to  obtain  an  uniform  mixture. 
It  is  best  to  mix  the  chopped  material  with  the  clay,  before 
the  water  is  put  to  it;  and  upon  adding  the  latter  to  effect 
the  mixture  at  first  by  stirring  up  the  mass  lightly  with  a  point- 
ed stick  or  fork :  it  will  then  be  found  easy  by  a  little  man- 
agement to  obtain  a  good  mixture  without  making  it  very 
moist.  If  the  fibres  be  long,  more  than  an  inch  in  length 
for  instance,  it  will  be  almost  impossible  to  mix  them  uni- 
formly with  the  lute,  and  they  will  interfere  much  with  its 
after  application.  Hay  cut  to  the  length  of  one  half  or  one 
third  of  an  inch,  is  a  very  good  substance  for  the  purpose. 

1093.  Retorts  coated  wfth  lute  thus  prepared  may  be  dried 
gradually,  without  the  production  of  any  considerable  cracks 
on  the  surface.     The  effect  of  these  intermixed  substances 
is  not  merely  to  confer  additional  tenacity  on  the  lute,  but  to 
give  a  direction  to  the  separations  which  are  formed  during 
the  contraction  occasioned  by  drying,  so  that,  ultimately,  in- 
stead of  having  the  lute  in  three  or  four  pieces,  with   large 
open  cracks  intervening,  the  separation  has  resulted  in  nu- 
merous minute  fissures.      These  do  not,  however,  prevent 
the  whole  from  adhering  together  as  one  coating ;  the  re- 
moval of  any  one  part  of  the  coating  far  from  its  original  sit- 
uation during  the  contraction  from  drying  is  thus  avoided, 
and  the  places  of  adhesion  between  the  tube  and  the  vessel 
are  more  generally  dispersed  and  more  numerous  than  before. 

1094.  A  similar  object  is  sometimes  obtained  by  applying 
a  bandage  of  coarse  canvass  or  other  open  wove  cloth  over 
the  surface  of  the  freshly  applied  lute  (699).     Thus  a  tube, 
when  coated  may  have  a  moistened  slip  of  such  canvass  car- 
ried round  it,  the  edges  of  each  turn  being  allowed  to  over- 
lap considerably,  the  whole  being  afterwards  rubbed  with  a 
little  moist  lute,  so  as  to  make  the  adhesion  between  the 
wrapper  and  the  coat  perfect.     When  dried,  the  lute  does 
not  crack,  and  the  coating  remains  whole,  but  it  has  a  ten- 
dency to  split  when  in  the  fire  in  the  direction  of  the  edges 


500  COATING — ITS  LIABILITIES IN  THE  FIRE. 

of  the  folds.  Where  the  form  of  the  vessel  is  such  as  to  pre- 
vent the  application  of  a  slip  of  cloth,  tow  or  hemp,  drawn 
out  into  lengths,  may  be  used  for  the  same  purpose;  but  it 
must  be  carried  over  the  surface  in  different  directions,  or  the 
cracks  will  not  be  prevented,  but  merely  a  direction  given  to 
them.  The  tow  envelope  should  be  afterwards  well  moist- 
ened with  soft  lute,  so  as  to  adhere  closely  to,  and  form  one 
mass  with,  the  coating. 

1095.  The  most  serious  evil  to  which  the  lute  or  coating 
is  liable  is  cracking  in  the  fire ;    and  unfortunately  this  evil 
increases  with  the  heat,  and  consequently  is  greatest  when  the 
coating,  if  good,  would  be  most  valuable  and  serviceable. 
A  luting  of  pure  clay  contracts  much  more  in  the  fire  than  a 
•luting  of  clay  mixed  with  as  much   sand  as  it  will  contain 
without  entirely  losing  its  plasticity  and  tenacity.     The  mix- 
ture of  sand  with  the  lute,  however,  renders  it  more  fusible; 
and  hence,  though  this  is  a  very  useful  expedient  when  the 
vessel  to  be  luted  has  not  to  support  more  than  a  bright  red 
or  a  yellow  heat,  it  is  not  applicable  with  equal,  or  with  any 
advantageous  effect,  when  very  high  temperatures  are  to  be 
sustained.    In  the  latter  cases  it  has  been  found  advantageous 
first  to  heat  a  portion  of  the  clay  intensely,  then  to  break 
it  small  and  use  it  instead  of  sand,  adding  so  much  to  the  re- 
cent clay  as  shall  leave  the  mass,  when  moistened  and  beat- 
en, with  such  a  degree  of  plasticity  and  adhesion  as  to  allow 
of  its  application.     If  access  can  be  had  to  a  glass-house, 
the  fragments  of  the  broken  glass  pots  may  be  pulverized 
and  used  instead  of  the  heated  clay,  particular  care  being  ta- 
ken that  all  parts  with  glass  upon  them,  or  with  the  exterior 
glaze  which  occurs  upon  glass  pots,  be  rejected.     Or  pulver- 
ized Hessian  or  Cornish  crucibles  may  be  used  for  the  same 
purpose ;  but  old  crucibles,  when  soiled  by  flux  or  other  im- 
purities, must  not  be  so  employed. 

1096.  Lute  which   has  had  fibrous  substances   diffused 
through  it  (1092)  does  not  separate  by  contraction  and  fall 
off  so  readily  as  that  which  is  altogether  earthy,  probably 
because  the  contraction  is  compensated  by  smaller   fissures 
in   greater    number.     Those  fibrous  matters    which  have 
comparatively  large  apertures,  as  hay,  straw,  dung,  &c.? 


COATING LUTING  OF  JOINTS.  501 

appear  to  be  the  best,  and  lute  which  has  been  mixed 
with  one  third  its  weight  of  pulverized  coke,  according  to 
Mr  Marshall's  method  of  making  crucibles  (647),  has  ap- 
peared to  be  improved  in  cases  where  the  luting  had  no  great 
weight  or  mechanical  power  to  resist. 

1097.  The  liability  to  crack  by  heat  in  all  these  coatings  is 
diminished  by  their  being  washed  over  when  dry  with  oil. 

1098.  Retorts,  flasks,  and  other  vessels  of  irregular  forms, 
are  sometimes  coated  by  being  dipped  into  a  thick  cream  of 
the  )ute  with  water,  and  sprinkling  dry  lute  over  them  during 
desiccation;   when  dry  they  are    again  to  be  immersed  in 
the  thin  paste  and  re-sprinkled,  and  the    process  repeated 
until  the  coat  which  they  have  received    is    of  sufficient 
thickness. 

1099.  All  coated  vessels  should  be  supported  as  much  as 
possible  when  in  the  fire  (599),  to  prevent  or  retard  the  de- 
rangement or  separation  of  the  lute  in  consequence  of  its 
weight. 

1100.  The  methods  of  luting  joints  vary  according  to  the 
joint  or  aperture  to  be  closed,  and  the  kind  of  lute  to  be  em- 
ployed.    In  the  time  of  Lavoisier,  accurate  joints  were  more 
essentially  necessary  than  at  present.     The  general  direc- 
tions then  given  were,  to  fix  the  apparatus  firmly,  and  to  ce- 
ment it  tightly  and  stiffly  by  strong  luting.     In  this  way 
many  complicated  instruments    were  combined    into   one 
great  apparatus,  so  rigid  in  all  its  parts  as  to  render  it  almost 
impossible  to  retain  every  junction  perfectly  close.     The 
number  of  these  junctions  has,  in  later  times,  been   very 
much  diminished,  and  the  introduction  of  elastic  caoutchouc 
connecters  (449)  has  almost  entirely  removed  that  rigidity 
which  was  so  dangerous  to  the  apparatus  and  fatal   to  its 
soundness. 

1101.  The  following  are  brief  accounts  of  various  lutes 
and  cements  that  may  be  advantageously  used  in  different 
circumstances. 

Stourbridge  clay :  it  should  be  ground  to  fine  powder  ;  is 
highly  useful  in  coating  retorts,  tubes,  &,c.,  and  in  effecting 
junctions  between  crucibles  and  their  stands.  It  is  to  be 


502  WINDSOR  LOAM — WILLIS'S  LUTE. 

applied  in  the  manner  already  described  (1084).     It  sustains 
a  higher  heat  than  any  other  English  lute. 

1 102.  Windsor  loam :  obtained  at  Hampstead,  &c.     It  is 
a  natural  mixture  of  clay  and  sand  in  such  proportions  as  to 
make  an  excellent  lute,  though  it  will  not  resist  the  heat 
sustained  by  Stourbridge  clay.     It  is  frequently  used  for  the 
lining  of  furnaces,  pots,  &c. 

1103.  These  lutes  are  also  very  useful  for  making  the  hot 
joints  of  metallic  vessels  tight,  as  for  instance,  the  iron  tube 
which  is  attached  to  an  oxygen  bottle  for  the  purpose  of  con- 
veying away  the  gas.     These  joints  are  generally  ground 
air-tight  at   first,  but  by  use  in   the  fire   soon  become    un- 
sound.    When  that  is  the  case,  a  little  smooth  and  rather 
soft  lute  should  be  mixed  up,  put  round  the  end  of  the  tube, 
and  the  latter  pressed  into  its  place.     Care  should  be  taken 
in  moving  the  apparatus  afterwards  that  no  agitation  or  blow 
be  given  it,  so  as  to  derange  the  junction  and  break  the 
continuity  of  the  lute. 

1104.  Willis's  lute.     When    earthenware   retorts   (491) 
are  required  to  be  rendered  impervious  to  air  or  vapours, 
Mr  Willis  directs  that  an  ounce  of  borax  be  dissolved  in  half 
a  pint  of  boiling  water,  and  as  much  slaked   lime  added  as 
will  make  it  into  a  thin  paste.     This  is  to  be  spread  over  the 
retort  with  a  brush,  and  when  dry,  a  coating  is  to  be  applied 
of  slaked  lime  and  linseed  oil  beaten  together  until  it  be- 
comes plastic.     This  will  dry  sufficiently  in  a  day  or  two, 
and  is  then  fit  for  use.     Earthenware  retorts  thus  prepared 
may  be  used,  it  is  said,  several  times  with  safety,  the  coating 
of  lime  and  oil  being  renewed  each  time. 

1105.  Mixtures  of  pulverized  borax  with  the  clay  lutes 
above  described,  or  with  common  clay,  form  fusible  fluxes, 
which  are  often  useful  in  glazing  over  the  surfaces  of  vessels 
so  as  to  close  their  pores.     About  one  tenth  by  weight  of 
borax  is  sufficient  for  the  purpose.     The  mixture  made  into 
a  thick  paste  with  water  may  be  laid  on  with  a  brush,  and 
the  vessel  should  be  handled  carefully  until  the  heat  has. at- 
tained redness,  lest  the  slightly  adhering  crust  should  be 
.knocked  off  previous  to  its  fusion. 

1106.  Fat  lute  is  applied  to  the  junctions  of  apparatus 


FAT  LUTE CEMENT PLASTER  OF  PARIS.  503 

which  are  liable  to  considerable  elevation  of  temperature,  or 
to  prevent  the  escape  of  corrosive  vapours  (475).  It  is 
prepared  by  beating  dried  and  finely  pulverized  clay  (pipe- 
clay or  Cornish  clay)  with  drying  linseed  oil,  until  the  mix- 
ture be  soft  and  ductile.  It  is  to  be  closely  applied  to  the 
junction  intended  to  be  made  tight,  the  glass  or  other  sub- 
stance being  first  wiped  perfectly  dry.  If  the  joint  has  to 
sustain  heat,  the  lute  will  soften ;  it  then  requires  to  be  con- 
fined by  strips  of  bladder,  which  being  put  round  it,  should 
be  tied  tightly  above  and  below  the  mass  of  lute,  and  after- 
wards two  or  three  turns  of  twine  passed  round  the  middle 
part.  When  moisture  or  vapours  escape  between  this  lute 
and  the  vessel,  it  is  very  difficult  to  close  the  leak,  and  hence 
the  great  importance  of  making  a  dry  tight  joint  at  the  com- 
mencement. Glazier's  putty  resembles  fat  lute,  and  may  be 
used  for  similar  purposes. 

1107.  Parker's  cement  is  a  brown  powder,  which  should 
be  preserved  for  use  out  of  contact  with  the  air.    When  mixed 
with  water  into  a  thin  paste,  it  gradually  sets,  and  becomes 
quite  solid  and  hard.     It  may  be  used  occasionally  with  ad- 
vantage in  making  joints  tight,  either  at  common  or  mode- 
rately high  temperatures.     It  may  be  rendered  quite  tight  by 
being  brushed  over  with  a  melted  mixture  of  equal  parts  of 
wax  and  oil.     It  resists  a  red  heat  sufficiently  well  to  make  it 
a  useful  coating  for  glass  retorts  or  tubes  upon  numerous  occa- 
sions. 

1108.  Plaster  of  Paris,  when  mixed  into  a  thick  cream 
or  thin  paste  with  water,  sets  after  a  short  time  and  becomes 
solid.     It  is  best  mixed  by  putting  a  little  water  into  a  cup, 
sprinkling  the  powder  into  it,  and  stirring  the  mixture.     It 
may  be  used  for  the  same  purposes  as  Parker's  or  Roman 
cement  (475),  being  generally  superior  to  it  in  convenience; 
and  may  be  made  air-tight  in  the  same  way  by  washing  it 
with  oil  or  wax  and  oil,  and  should  also  be  preserved  from 
the  air  when  in  powder.     When  Plaster  of  Paris  is  mixed  up 
with  very  weak  glue  instead  of  water,  it  is  somewhat  longer 
before  it  solidifies,  but  ultimately  makes  a  very  hard  and 
strong  lute. 

1109.  A  lute  of  Plaster  of  Paris  may  be  raised  to  dull  red 


504  LUTES LIME  AND  EGG. 

heat  without  injury,  but  if  oiled  or  waxed  to  prevent  the 
passage  of  vapours,  it  will  not  support  so  high  a  temperature 
unchanged. 

1110.  Caustic  lime,  mixed  with  various  mineral  and  vege- 
table substances  in  solution,  affords  numerous  cements  and 
lutes,  which  when  dry  are  hard,  and  impervious  to  vapours. 
The  lime  should  be  well  burnt,  and  slaked  with  just  sufficient 
water  to  make  it  fall  into  a  dry  powder;  after  which  it  should 
be  preserved  in  a  close  bottle  until  wanted..    One  of  the  most 
powerful  of  these  cements  is  obtained  by  using  white  of  egg 
diluted  with  its  bulk  of  water.     The  fluids  are  to  be  beaten 
together  until  the  mixture  pours  with  perfect  liquidity.     This 
is  best  effected  by  means  of  a  little  stick  made  to  rotate  by 
rolling  it  between  the  hands,  and  having  at  its  lower  end  a 
cross  piece,  the  arms  of  which,  when  in  motion  and  immersed 
in  the  liquids,  effectually  mix  them.    This  being  done,  the  dry 
slaked  lime  in  powder  is  to  be  added  by  sprinkling  in  such 
quantities,  that  the  whole  when  mixed  shall  have  the  consist- 
ency of  thin  paste.     This  should  be  done  quickly,  after  which 
the  mixture  should  be  put  upon  slips  of  cloth  and  applied 
round  the  junction  to  be  luted,  and  a  little  of  the  dry  lime 
should  be  sprinkled  over  the  exterior.     The  substance  soon 
hardens  and  adheres  strongly. 

1111.  This  cement  is  often  conveniently  applied  by  moist- 
ening slips  of  cloth  with  white  of  egg  beaten  up  without  the 
addition  of  water,  and  then  sprinkling  the  lirne  in  powder  over 
it,  in  such  quantity  as  to  make  a  moist  paste  on  the  cloth. 
The  slips  should  be  immediately  applied  to  the  junction,  a 
little  lime  being  shaken  over  the  exterior. 

1 1 12.  In  place  of  white  of  egg,  a  moderately  strong  solu- 
tion  of  glue  may  be  used;  or  the  serum  of  blood;  or  diluted 
blood;  or  a  mixture  made  by  rubbing  down  very  poor  cheese 
with  water  in  a  mortar,  until  of  the  consistency  of  cream. 

1113.  If  a  leak  take  place  through  or  by  one  of  these  lime 
lutes  during  an  operation,  no  difficulty  occurs  in  stopping  it 
by  the  application  of  a  fresh  portion  of  the  lute,  which  adheres 
readily  and  perfectly,  and  is  not  liable  to  the  difficulty  which 
occurs  with  fat  lute.     They  will  bear  a  heat  approaching  to 
visible  ignition  without  injury. 


IRON  CEMENT— WHITE  LEAD BLADDER.  505 

1114.  Iron  cement.     This  mixture   is    used  for    making 
permanent  joints  generally  between  surfaces  of  iron,    dean 
iron   borings,  or  turnings,  are  to  be  slightly  pounded,  so  as 
to  be  broken  but  not  pulverized;  the  result  is  to  be  sifted 
coarsely,  mixed  up  with  powdered  sal  ammoniac  and  sulphur, 
and  enough  water  to  moisten  the  whole  slightly.     It  is  then 
to  be  rammed  or  caulked  into  the  joints,  and  the  latter  drawn 
together  as  tightly  as  possible.     The  proportions  are,  1  sul- 
phuf,  2  sal  ammoniac,  80  iron;  and  no  more  should  be  mix- 
ed than  can  be  used  at  once. 

1115.  White  lead  ground  up  with  oil,  when  spread  upon 
slips  of  cloth,  is  very  useful  for  making  joints  tight,  especially 
those  of  metal,  glass  or  other  tubes.     The  lead  when  laid  on 
the  cloth  should  be  made  to  penetrate  it.     The  slips  should  be 
drawn  tightly  round  the  joint,  and  then   bound  with  twine, 
the  ends  of  the  joints  being  tied  first,  and  afterwards  the 
middle.     Sometimes  tow  is  used  with  the  white  lead  instead 
of  cloth;  it  should  then  be  so  laid  over  the  joint  as  to  allow 
the  fibres  to  pass  each  other  and  the  joint  obliquely,  that 
lateral  strength  may  be  given  to  it. 

1116.  Bladder.     Moistened  bladder  is  in  constant  requisi- 
tion in  the  laboratory  for  closing  joints;  when  soaked  for 
some  time  in  water  either  warm  or  at  common  temperatures, 
it  becomes  clammy,  is  very  adhesive,  and  adheres  well  to 
glass.     It  should   be  cut  into  slips  of  the  proper  size,  and 
then  applied  as  a  bandage  to  the  place.     It  does  not  always 
require  the  application  of  twine  to  keep  it  in  its  situation, 
so  that  occasionally,  when  inconvenient,  tying  may  be  dis- 
pensed with. 

If  after  being  soaked  it  b£  wiped  dry  with  a  cloth,  and 
then  moistened  on  the  surface  with  white  of  egg,  its  adhe- 
sion is  increased,  and  the  use  of  twine  rendered  quite  unne- 
cessary. 

1117.  Paste  and  Paper  are  frequently  useful  in  making 
joints.     The  paste  should  be  well  boiled  and  thick.     It  is 
better  to  use  bibulous  than  sized  paper,  for  the  paste  more 
freely  enters  its  pores  and  incorporates  with  it,  and  the  joint 
is  less  permeable ;  but  from  the  greater  tenderness  of  such 
paper  when  moist,  more  care  is  required  in  handling  the 

3  O 


506  PASTED  PAPER GLUE MEAL CAOUTCHOUC. 

pasted  slips  and  applying  them.  If  sized  paper  be  used,  the 
pasted  surface  should  be  doubled  inwards,  then  redoubled 
several  times,  and  left  for  a  few  minutes  to  soak:  evaporation 
is  thus  prevented,  and  the  paste  and  paper  preserved  moist. 
When  opened  out,  the  pasted  surfaces  should  not  be  sepa- 
rated from  each  other,  until  the  doubled  paper  has  been  cut 
into  slips  of  the  size  required. 

1118.  Paper  which  has  been  pasted,  and  has  been  allow- 
ed to  dry  without  having  been  folded  together,  is  very  use- 
ful in  the  laboratory.     A  slip  of  it  moistened  on  the  pasted 
side,  and  allowed  to  soak  for  a  few  moments,  is  ready  for  ap- 
plication to  a  joint,  or  in  any  other  situation  where  its  adhe- 
sive powers  may  be  useful.     It  is  also  very  convenient  for 
making  labels,  to  be  attached  to  bottles  and  glasses  the  in- 
stant they  are  required  (1303,  1345). 

1119.  Paper  prepared  with  a  mixture  of  wax  and  turpen- 
tine is  also  very  useful  for  many  of  these  purposes,  especially 
the  labelling  of  bottles  (1345). 

1120.  Glue  with  paper  makes  a  very  useful  and  conveni- 
ent application.     With  cloth  it  makes  a  strong  one,  which 
may  be  rendered  nearly  tight  by  an  exterior  fold  of  paper, 
and  quite  tight  if  the  joint  when  dry  is  brushed  over  with 
drying  oil,  or  drying  oil  and  wax  (1107). 

1121.  Linseed  meal  or  almond  paste,  well  beaten  up  with 
water  until  of  an  uniform  and  proper  consistence,  is  an  ex- 
cellent lute  for  cold  joints  of  glass  (475),  or  metal  appara- 
tus.    It  should  be  applied  thickly,  and  will  then  adhere 
well :  it  will  in  some  hours  become  a  hard  mass,  and  will 
resist  most  vapours;  but  water  must  not  be  allowed  to  run 
upon  it,  either  within  or  without  the  joint     It  will  not  bear 
a  heat  above  600°  Fahrenheit.     When  made  up  with  milk, 
lime-water,  or  weak  glue,  it  becomes  firm  sooner,  and  forms 
a  harder  substance  than  when  water  alone  is  used. 

1122.  Caoutchouc.    Connecters  of  this  substance  have 
been  already  referred  to  and  described  (449).     Joints  may 
be  made  tight  by  means  of  them,  and  consequently  stiff  tubes 
may  be  dispensed  with,  in  a  great  number  of  instances. 
These  connecters  when  applied  should   be  tied  round  the 
edges  with  twine,  but  not  be  drawn  so   tightly  as  to  incur 
any  risk  of  cutting  the  caoutchouc,  for  a  slight  degree  of 


CAP-CEMENT WAX SOFT  CEMENT.  507 

tension  is  sufficient  to  make  the  joint  secure.  When  the 
caoutchouc  tubes  require  slight  extension  to  make  them  pass 
over  the  joints,  their  own  contraction  is  generally  sufficient 
to  make  their  contact  with  the  tube  (if  of  glass)  perfectly 
air  tight.* 

1123.  Cap-cement.     This  is  one  of  the  numerous  cements 
which  contain  resin  or  wax,  and  are  applied  for  causing  ad- 
hesion, or  making  close   joints  at  common   temperatures. 
Their  principal  use  is  with  pneumatic  apparatus  belonging 
to  the  air-pump,  and  the  water  and  mercurial  trough.     Cap- 
cement  is  used  for  the  attachment  of  caps  to  retorts  in  the 
manner  described  (833).     It  may  be  formed  of  5  parts  by 
weight  ef  resin,  1  part  of  yellow  bees'  wax,  and  1   part  of 
red  ochre  or  Venetian  red  in  fine  powder.     The  earthy  sub- 
stances should  be  well  dried  in  an  evaporating  basin  on  the 
sand-bath,  at  temperatures  above  212°.     The  wax  and  resin 
should  be  melted  together,  the  powder  stirred  in  by  degrees, 
and  the  heat  continued  a  little  above  212,  until  all  frothing 
ceases  and  the  mixture  becomes  tranquil.     It  is  then  to  be 
cooled,  the  stirring  being  continued,  until  it  has  become  so 
thick  that  no  probability  remains  of  the  'separation  of  the 
matters  by  standing. 

1124.  Yellow-wax  may  frequently  be  made   to  answer 
the  purposes  of  a  cement.     It  resists  most  acid   fumes  at 
common  temperatures,  and  hence  is  often  applied  not  merely 
for  making  the  joints  of  apparatus  used  in  operations  with 
acids,  but  even  for  coating  or  lining  vessels  intended  for  the 
retention  of  peculiar  vapours  and  liquids,  as  those  of  the 
compounds  of  fluorine,     It  will  not,  however,  resist  the  ac- 
tion long.     It  is  less  brittle  (though  more  fusible)  if  melted 
with  one  eighth  its  weight  of  common  turpentine.     It  should 
be  moulded  into  cylinders  or  sticks,  and  thus  preserved  for 
use. 

1125.  Soft  cement  consists  of  yellow  wax,  melted  with  its 
weight  of  turpentine  and  a  little   Venetian  red  to  give  it 
colour.     When  cold,  it  has  the  hardness  of  soap,  but  by  the 

*  A  strap  of  sheet  gum-elastic,  wound  round  the  joint  tightly,  affords  perfect 
security.  Twine  should  be  applied,  not  to  tighten  the  wrapper,  but  to  prevent  it 
from  unfolding  itself.— ED. 


508  SOFT  CEMENT. 

warmth  of  the  fingers  and  a  little  pressure  it  becomes  pliant, 
and  may  be  moulded  into  any  form  required.  It  is  very 
serviceable  in  many  hasty  operations  at  common  tempera- 
tures, as  making  a  tube  and  cork  tight  into  the  neck  of  a 
flask  (484) ;  closing  the  apertures  where  tubes  have  passed 
through  vessels  which  are  afterwards  to  be  filled  with  water; 
inclosing  deliquescent  substances  in  tubes  (973),  stopping  a 
sudden  leak,  &c.  In  all  these  cases  it  requires  merely  to 
be  moulded  into  form  and  pressed  upon  the  joint  in  a  dry 
state,  and  will  then  adhere  perfectly.  It  will  not  adhere  to 
wood  or  other  porous  substances  in  a  moistened  state,  but 
in  cases  of  necessity  it  may  be  made  to  adhere  to  wet  metal 
and  glass.  The  surface  of  cement  to  be  applied  should  then 
be  of  a  convex  form  at  first,  that  as  it  meets  with' and  adapts 
itself  to  the  surface  to  which  it  is  to  adhere,  it  may  thrust 
the  water  before  it ;  more  care  than  is  ordinarily  required 
should  afterwards  be  given  to  press  the  cement  into  perfect 
contact. 

1126.  Soft  cement  is  better  for  joints  of  apparatus  which 
are  liable  to  be  shaken  during  the  operations  performed  in 
them  than  hard  cement  or  lutes,  for  it  allows  of  a  degree  of 
motion  which  would  infallibly  cause  the  separation  of  the 
hard  substance  from  the  glass  or  metal,  and  so  occasion 
leakage.     It  not  unfrequently  happens  that   this  allowable 
motion  is  a  cause  .of  safety  to  the  vessels  by  permitting  such 
slight  changes  of  adjustment  as  are  sufficient  to  relieve  the 
apparatus  from  any  degree  of  tension  or  irregular  bearing, 
which  may  have  occurred  during  the  experiment,  and  which, 
if  not  thus  allowed  for,  might  endanger  the  fracture  of  the 
weaker  parts  (854). 

1127.  The  mouths  of  bottles  which  contain  gases,  mine- 
ral waters,  or  acids,  whether  corked  or  stoppered,  are  fre- 
quently covered  with  cement  to  render  them  perfectly  tight. 
In  these  cases  soft  cement  is  very  superior  to  hard  cement, 
or  sealing-wax,  being  much  more  likely  to  retain  its  adhe- 
sion to  the  glass  during  travelling.     The  top  of  the  bottle, 
with  the  cork  or  stopper,  should  be  made  quite  dry,  and  the 
cement  then  applied  all  over  it  to  a  considerable  thickness. 
After  being  pressed   into  its  place?   the  whole  should  be 


SOFT  CEMENT POWDERED  GUM.  509 

covered  with  a  piece  of  moistened  bladder  or  cloth,  and 
tightly  tied  down.  When  the  object  is  to  preserve  a  corked 
bottle  of  water  or  any  other  substance  having  no  action  upon 
the  soft  cement,  it  is  well  to  melt  a  little  of  the  latter,  to  dip 
the  cork  into  it  (973),  and  having  previously  dried  the  neck 
of  the  bottle  within,  immediately  to  thrust  it  into  Its  place, 
and  then  to  proceed  as  above.  In  this  way  many  waters 
containing  carbonic  acid,  and  holding  particular  substances 
in  solution,  may  be  sent  to  a  considerable  distance  with 
scarcely  any  change. 

1 128.  Soft  cement  is  also  very  useful  for  taking  up  small 
particles,  as  crystals  or  fragments  of  bodies,  for  the  purpose 
of   submitting  them    to  ocular  examination.     It  is  easily 
moulded  between  the  fingers  into  an  acute  cone,  the  fine  ter- 
mination of  which  being  brought  into  contact  with  the  body, 
adheres  to  it  by  a  mere  point,  with  sufficient  power  to  sup- 
port it,  and  allow  its  examination  in  any  position.     It  is  also 
convenient  for  effecting  the  adjustment  of  any  crystal  or  re- 
flecting body  placed  upon  it,  in  the  desired  position ;  a  cir- 
cumstance which  makes  it  serviceable  in  experiments  on  light 
or  with  the  reflective  goniometer. 

1 129.  Powdered  gum  should  be  retained  in  the  laboratory, 
as  supplying  a  ready  means  of  attaching  paper  labels  to  bot- 
tles, minerals,  or  other  articles.    A  little  of  the  powder  stirred 
up  by  the  finger  with  a  drop  of  water,  if  necessary,  upon  the 
label  or  paper  itself,  is  ready  for  immediate  application. 
Paper  which  has  been  covered  on  one  side  with  a  thick  so- 
lution of  gum,  and  dried,  is  useful  in  the  same  manner  as  the 
pasted  paper  already  described  (1118),  but  there  are  few 
bodies  to  which  gum  adheres  so  well  as  paste,  and  the  for- 
mer almost  always  separates  from  glass.     The  best  kind  of 
prepared  paper  is  made,  by  using  a  paste  formed  of  equal 
parts  by  bulk,  of  flour  and  powdered  gum,  and  a  small  quan- 
tity of  alum;   these  being  mixed  with  sufficient  water  to 
make  them  into  a  thin  cream,  are  to  be  heated  in  an  evapo- 
rating basin  and  continually  stirred  until  they  boil ;  the  ebulr 
lition  is  to  be  continued  a  few  minutes,  but   evaporation 
should  be  prevented  as  much  as  possible,  lest  the  paste  be- 
come too  thick.     If  that  happen,  a  little  more  water  should 


510  LEAKS  DETECTED — STOPPED. 

be  added,  and  the  whole  well  mixed  together.  This  paste 
is  to  be  applied  to  one  side  of  the  paper,  and  allowed  to  dry 
as  before  described  (1118). 

1130.  When  a  leak  occurs  at  a  luted  joint,  or  at  any  other 
part  of  the  apparatus,  it  is  often  necessary  to  search  for  the 
exact  place  of  the  aperture.     If  the  vapours  or  gases  which 
issue  are  acid,  the  place   may  be  detected  by  bringing  a 
piece  of  paper  dipped  in  solution  of  ammonia  towards  it; 
fumes  will  be  produced.     If  they  are  ammoniacal,  then  a 
little  muriatic  acid  on  paper,  or  a  glass  rod,  will  detect  the 
aperture  whence  they  issue.     If  the  vapours  are  aqueous,  the 
spot  may  frequently  be  found,  by«  bringing  a  cold  glass  plate, 
or  the  surface  of  a  bottle  towards  it,  the  condensation  and 
dimness  on  the  cold  surface,  leading  to  the  aperture.     On 
other  occasions,  a  small  taper  flame  may  be  brought  near,  the 
bias  given  to  the  flame,  when  it  comes  across  the  issuing 
current,  or  the  actual  inflammation  of  the  vapours,   will 
show  the  spot  where  they  find  vent.     When  it  can  be  al- 
lowed, that  is,  where  the  heat  is  not  great,  and  the  luting 
will  not  be  injured  by  a  little  water,  a  thick  solution  of  soap- 
suds, or  of  gum,  or  paste,  may  be  washed  over  the  suspected 
place :  a  bubble  will  be  blown  over  the  aperture  at  which 
the  gaseous  contents  of  the  apparatus  issue  forth. 

1131.  The  leak  thus  found  must  be  stopped  by  applying  a 
little  soft  cement  (1125),  or  fat  lute  (1106),  or  lime  and 
white  of  egg  (1110),  or  paste  and  paper  (1118),  according  to 
the  nature  of  the  lute  originally  used,  and  other  circumstan- 
ces.    Many  leaks,  which  can  hardly  be  remedied  in  any  other 
way,  may  be  stopped  by  tying  a  piece  of  sheet  caoutchouc 
(449)  upon  them.* 

*  For  further  instruction  relative  to  the  subject  of  this  section,  see  Lavoisier's 
Elements  of  Chemistry,  chap.  vi.  sect.  5,  and  Aikins's  Chemical  Dictionary,  vol. 
i.  p.  273. 


GLASS-BLOWING — APPARATUS HEATING.  511 

SECTION  XIX. 
BENDING,  BLOWING,  AND  CUTTING  OF  GLASS. 

1132.  MANY  occasions,  upon  which  a  knowledge  of  the 
methods  of  softening,  bending,  and  blowing  of  glass  by  means 
of  a  lamp  and  blow-pipe  would  be  useful,  have  been  already 
mentioned  (130,  463,  559,  &c.).    The  attainment  of  a  ready 
practice  on  these  points,  together  with  that  of  facility  in  ef- 
fectually substituting  an  apparatus  or  vessel  at  hand,    for 
another  that  is  wanting,  are,  perhaps  of  all  experimental  ac- 
quirements, those  which  render  the  chemist  most  indepen- 
dent of  large  towns  and  of  instrument-makers. 

1133.  The  apparatus  necessary  for  the  most  effectual  prac- 
tice of   this  kind,  is  the  table  blow-pipe  already  described 
(242),  the  precautions  with  regard  to  the  state  of  the  flame, 
which  have  been  pointed  out,  being  particularly  attended  to. 
The  methods  of  working  glass  with  this  instrument  will  be 
first  described,  and  afterwards  the  best  mode  of  supplying 
its  deficiency,  by  means  of  the  common  spirit-lamp  and  mouth 
blow-pipe.    The  chemist's  operations  are  generally  confined 
to  glass  in  the  form  of  tube  or  rod;  but  though  thus  limited, 
they  are  daily  useful,  and  it  is  only  by  practice  and  the  fre- 
quent performance  of  such  manipulatory  processes  as  those 
described  in  Section  XVI.,  that  any  adequate  idea  of  their 
great  value  and  service  can  be  obtained. 

1134.  Supposing  the  operator  sittingbefore  the  table  (242), 
the  lamp  trimmed  and  burning,  the  bellows  put  in  action  by 
the  foot,  and  the  flame  clear,  pointed,  and  steady,  it  will  be 
desirable,  in  the  first  place,  to  consider  the  particular  circum- 
stances requiring  his  attention,  whilstraisingthe  middle  or  the 
end  of  a  piece  of  glass  tube  to  a  red  heat,  and  also  whilst  cool- 
ing it  to  its  first  temperature.     This  is  the  simplest  case  re- 
quiring instruction,  and  mu$t  be  performed  with  facility  and 
readiness,  before  any  further  steps  tie  taken.     If  the  tube  is 
to  be  heated  in  the  middle,  its  ends  may  be  supported  by  the 
fingers  of  each  hand,  so  that  the  hands  shall  bo  beneath  them, 


512  GLASS  TUBE HEATED THICK  AND  THIN. 

with  the  palms  upwards;  and  the  arms  may  be  rested  (till  by 
practice  they  have  acquired  steadiness)  upon  the  edge  of  the 
table.  The  part  to  be  heated  is  to  be  brought,  not  into  the 
flame,  but  into  the  current  of  hot  air  which  passes  off  in  the 
same  direction  as  the  flame  from  it  (1142),  and  the  tube  is  to 
be  turned  so  as  to  become  heated  all  round,  and  also  moved 
a  little  to  the  right  and  left,  that  the  temperature  of  the 
neighbouring  parts  may  be  raised.  After  a  few  seconds, 
when  the  glass  has  become  hot,  it  should  be  brought  towards 
the  point  of  the  flame  (220,  244),  and  ultimately  into  it,  being 
turned  round  all  the  time,  and  also  moved  laterally,  though 
not  to  the  same  extent  as  before,  that  the  heat  may  be  gene- 
rally applied.  By  the  time  that  the  tube  (supposed  to  be 
about  half  an  inch  in  diameter,  and  one-tenth  of  an  inch  in 
thickness)  is  within  the  flame,  occupying  a  place  about 
midway  between  the  commencement  and  end  of  the  nearly 
transparent  part  (229,  232),  it  should  be  of  a  bright  red  or 
yellow  heat,  to  the  width  of  half  an  inch  all  round,  so  as  to 
be  perfectly  soft  at  that  part;  and  the  heat  should  gradually 
diminish  from  it  on  each  side,  towards  those  parts  which 
are  still  but  little  above  common  temperatures. 

1135.  The  tube  is  brought  at  first  into  the  heated  air, 
and  not  into  the  flame,  because  the  hasty  application  of  heat 
endangers  fracture.     Glass  suddenly  heated  breaks,  because 
a  part  is  rendered  hot  directly  in  the  neighbourhood  of  a  cold 
part,  and  expanding,  tears  the  cold  and  unexpanded  part 
asunder.     But  when  the  heat  is  gradually  applied,  it  has  time 
to  diffuse  itself  over  the  neighbouring  parts,  so  that  no  con- 
tiguous portions  have  such  differences  of  temperature  as  to 
occasion  differences  of  expansion  greater  than  the  glass  can 
allow,  without  separation  of  continuity.     Hence  the  reason 
why  the  heat  is  directed  to  be  applied  gradually  ;  and  hence 
the  reason  also  why  the  parts  near  to  the  particular  spot  re- 
quiring to  be  heated  are  also  purposely  raised  in  temperature. 

1136.  Thin  glass,  being  heated  through  more  rapidly  than 
thick,  requires  less  precaution  than  the  latter:  sometimes  but 
little  previous  warming  will  be  necessary  for  it,  and  on  other 
occasions  it  may  be  brought  directly  into  the  flame.     Some 
tubes  are  so  small  and  thin  that  it  will  be  found  impossible  to 


GLASS  HEATED DISCOLORATION.  513 

break  them  by  the  most  sudden  application  of  the  flame  ; 
whilst  with  large  and  thick  tubes  it  will  be  found  almost 
equally  impossible  to  heat  them  without  making  them  fly  to 
pieces.  The  precaution  adopted  must  be  in  proportion  to  the 
size  and  thickness  of  the  tube,  and  by  a  little  practice  will 
soon  be  duly  appreciated. 

1137.  When  the  end  of  the  tube  is  to  be  heated  instead 
of  the  middle,  more  care  is  required,  in  consequence  of  the 
great  facility  with  which  cracks  commence  at  an  edge.     A 
heat  which  would  cause  no  danger  if  applied  to  the  middle 
of  a  tube,  would  instantly  cause  the  extremity  to  fly  to  pieces. 
In  such  cases  it  is  best  to  begin  by  warming  the  tube  an  inch 
or  a  little  more  from  the  end,  and  from  thence  to  proceed 
slowly  to  the  end ;  always  keeping  the  temperature  of  the 
part  first  heated  rather  higher  than  that  of  the  end,  until  the 
glass  softens,  which  will  be  below  a  visible  red  heat  in  day 
light;  after  that,  the  end  is  safe,  and  the  highest  heat  may  be 
applied  there. 

1138.  The  glass  must  not  be  blackened  or  discoloured 
during  the  operation  of  heating.     This  is   a  fault  that  may 
happen  from  either  of  two  circumstances,  namely,  the  incor- 
poration of  charcoal  with  the  glass,  or  the  reduction  of  the 
oxide  of  lead  in  it.     When  glass  below  a  red  heat  is  brought 
into  the  bright  part  of  the  flame*,  a  coat  of  charcoal  is  de- 
posited, which  in  many  cases  does  not  disappear  as  the  heat 
rises  above  redness,  because  of  the  incorporation  of  the  char- 
coal with  the  melted  glass;  and  occasionally  it  even  increases 
in  quantity.     Being  thus  brought  into  contact  with  the  oxide 
of    lead  in  the   glass,   that    substance  is  decomposed  by 
the  carbonaceous  matter,  and  the  lead,  being  reduced,  forms 
another  kind  of  stain  which  mingles  with  the  former.     When 
the  stain  happens  by  accident,  it  is  removed  by  bringing  the 
glass  to  the  apex  of  the  flame,  that  the  oxygen  of  the  air  may 
act  upon  it ;  and  if  the  discolouration  be  superficial,  it  is  soon 
reduced  and  disappears.     But  this  process  is  often  inconveni- 

*  The  brightness  of  the  flame  depends  upon  the  presence  of  particles  of 
charcoal  ignited  in  it.  See  Sir  H.  Davy  on  Flame,  Quarterly  Journal  of  Science, 
ii.  124. 

3   P 


514  GLASS  HEATED POWERS  OF  FLAME. 

ent,  because,  during  the  time  the  charcoal  is  burning  away, 
and  the  lead  becoming  oxidized,  the  glass,  which  is  ne- 
cessarily in  a  melted  state,  is  gathering  together  and  thicken- 
ing, or  is  contracting  into  inconvenient  forms. 

1 139.  If  after  the  glass  has  been  raised  to  a  full  heat  with- 
out any  stain,  it  be  brought  into  the  bright,  or  especially  the 
smoky  part  of  the  flame,  a  part  of  the  oxide  of  lead   is  im- 
mediately reduced,  and  a  stain  occasioned.     This  should  be 
immediately  rectified,  and  removed  as  before,  but  it  is  far 
better  that  it  should  be  altogether  avoided. 

1 140.  The   heat  produced  should  not  be  irregular    or 
patchy,  varying  with  every  turn  or  motion  of  the  glass,  but 
uniform  all  round  a  certain  length  of  the  tube;  the  greater 
the  length  which,  by  the  turning  and  lateral  motions  of  the 
tube,  can  be  thus  retained  at  a  fair  uniform  red  heat,  the 
greater  and  more  efficient   is  the  skill  of  the  operator.     To 
this  end  it  will  occasionally  be  found  advantageous  to  incline 
the  tube  towards  the  direction  of  the  flame,  and  not  to  hold 
it  directly  across 

1141.  After  having  proceeded  thus  far  successfully,  the 
operator  should  vary  the  temperature  and  obtain  the  power 
of  governing  it;  sometimes  retaining  the  tube  at  a  low  red- 
heat  by  carrying  it  out  of  the  flame;  or  raising  it  to  as  high 
a  temperature  as  possible,  by  bringing  it  into  the  flame;  or  by 
confining  the  greatest  heat  to  a  narrow  ring,  or  extending  it 
as  before  mentioned  over  a  broad  one. 

1142.  By  this  kind  of  practice,  a  knowledge  of  the  heating 
power  of  different  parts  of  the  flame  will  be  acquired.     It 
will  be  found  greatest  within  the  pale  flame  just  before  the 
point  of  the  bright  flame  (229),  and  that  part  will  also  heat 
the  greatest  quantity  of  matter.     Its  power  will  diminish 
towards  the  extremity,  though  it  will  still  be  very  considerable, 
and  capable  of  heating  a   large  tube.     The  current  of  air 
which  issues  from,  and  may  be  considered  as  a  prolongation 
of  the  flame,  should  also  be  properly  appreciated  (234).     It 
has  the  power  of  keeping  glass  at  a  visible   red  heat  at  the 
distance  of  two  or  three  inches  from  the  point  of  the  flame, 
and  is  of  constant  use  in  annealing  tube  and  tube  apparatus, 
both  in  raising  and  lowering  its  temperature  (1134,  234). 


HEATED  GLASS ITS  SOFTNESS.  515 

1143.  Besides  this  examination  of  the  flame  in  the  direc- 
tion of  its  length,  it  should  also  be  investigated  laterally,  as 
regards  the  power  it  possesses  over  a  piece  of  tube,  placed 
directly  across  and  through   it,  compared  with  that  which  it 
exerts,  when  the  tube  is  a-little  above  or  below  the  axis  of 
the  cone. 

1144.  In   this  manner  every  variation  produced  by  ap- 
proaching the  glass  in  different  directions  to  the  hottest  part 
of  the  flame,  may  be  ascertained  and  fixed  in  the  mind.     The 
glass  worker,  instead  of  varying  the  temperature  of  his  source 
of  heat,  varies  the  position  of  his  material  in  relation  to  it,  and 
thus  gains  command  of  all  temperatures,  up  to  the  highest 
which  the  flame  can  produce.     The  more  perfectly  he  knows 
the  necessary  position,  and  the  more  readily  he  applies   his 
knowledge  and  attains  the  temperature  required,  the  quicker 
and  the  better  will  his  operations  be  performed. 

1145.  Besides  the  difference  of  heat  dependent  upon  the 
different  parts  of  the  flame  in  which  the  glass  is  placed,  much 
depends  upon  the  size  and  thickness  of  the  tube  itself.     It 
must  be  a  powerful  flame,  and  well  managed,  that  will  fully 
heat  an  inch  in  length  of  the  middle  of  a  glass  tube  two-thirds 
of  an  inch  in  diameter,  and  the  eighth  or  more  of  an  inch  in 
thickness.     But  a  tube  half  an  inch  in  diameter  is  easily  heat- 
ed ;  and  when  thin,  or  of  much  smaller  size,  care  is  actually 
required  that  it  be  not  brought  into  the  most  powerful  part 
of  the  flarne,  and  become  so  over  heated  and  soft,  as  to  be 
unmanageable.     Practice  alone  affords  a  perfect  acquaint- 
ance with  these  points :  the  size  and  thickness  of  tube,  the 
state  of  the  flame  itself,  and  its  power  in  different  parts,  va- 
rying almost  infinitely. 

1146.  The  softness  of  the  glass  depends  upon  the  tempera- 
ture to  which  it  is  subjected.     It  begins  to  soften  and  bend 
below  a  visible  red  heat,  and  when  in  small  portions  is  easily 
brought  to  a  semi-fluid  state.     The  condition  of  the  glass  is 
judged  of  as  much  by  the  fingers  as  the  eye ;  the  feeling 
which  the  hands  appreciate  of  bending  with  greater  or  less 
facility,  or  of  giving  way  more  or  less  readily  as  the  ends  are 
pushed  or  pulled,  is  a  better  .criterionas  to  the  proper  mo- 
ment of  working  it  than  the  appearance.     Glass,  being*  a 
transparent  substance,  does  not  assume  such  striking  appear- 


516  HEATED  GLASS — APPEARANCE — BENT. 

ances,  when  ignited  to  different  degrees,  as  opaque  bodies, 
and  its  visible  red  heat  is  far  higher  than  the  visible  red  heat 
of  metal  or  charcoal.  Hence  it  is  that,  if  the  glass  has  be- 
come stained  as  above  described  (1138),  those  parts  will  ap- 
pear red-hot  long  before  the  glass.  Notwithstanding  these 
circumstances,  glass  when  highly  heated  becomes  visibly 
ignited,  and  these  appearances  help,  together  with  the  feel, 
to  indicate  its  state.  When  of  moderate  thickness,  the  glass, 
in  consequence  of  the  oxide  of  lead  that  is  in  it,  assumes  a 
greenish  yellow  tinge  when  heated;  this  occurs  before  a  red 
heat,  and  helps  with  other  circumstances  to  indicate  its  state. 
The  experimenter  should  make  himself  well  acquainted  with 
these  indicative  appearances. 

1147.  When  the  tube  is  in  a  thoroughly  heated  state,  the 
experimenter  should  bend  it ;  draw  it  out  so  as  to  render  it 
thinner ;   and    press  it  up  again  to  increase  its  thickness. 
Stopping  one  end  with  his  finger,  and  applying  his  mouth  to 
the  other,  he  should  also  blow  it  out  and  expand  it;  and  by 
introducing  a  smooth  piece  of  thick  iron  wire  into  a  tube 
heated  at  the  end,  he  should  observe  in  what  manner  it  gives 
way  to  the  pressure,  and  to  what  extent  it  may  be  moulded 
(1163).     He  will  find  that  the  glass  may  be  bent  as  soon  as 
it  yields  in  the  hands;*  that  it  must  be  much  hotter  before  it 
can  be  properly  drawn  out  or  pressed  up  again  and  thickened; 
and  that,  generally,  the  heat  must  be  still  higher  for  blowing 
and  moulding.     These  comparative  but  necessary  degrees 
of  softness  should  be  observed  and  remembered,  as  also  the 
variations  necessary  for  tubes  of  different  thicknesses ;  thin 
tube  is  worked  generally  at  lower  temperatures  than  that 
which  is  thick. 

1148.  The  experimenter  should  also  acquire  that  steadi- 
ness yet  lightness  of  hand,  and  that  power  of  retaining  the 
tube  between  the  fingers,  which  is  necessary  to  prevent  the 
distortion  of  soft  glass.     When  heating  a  tube  in  the  middle, 
it  is  impossible,  whilst  all  is  hard,  not  to  hold  it  in  a  straight 
position,  and  any  slight  irregular  strain  or  pull  does  no  harm. 

*  Although  glass  may  be  bent  at  a  comparatively  low  temperature,  its  curves 
should  be  made  at  a  higher  one,  because  then  the  particles  are  enabled  to  accom- 
modate themselves  to  the  new  position,  unequal  tension  is  avoided,  and  the  ten- 
dency to  spontaneous  fracture  is  in  a  great  degree  obviated. — ED. 


HEATED  GLASS— SUPPORTED COOLED.        517 

But  when  the  heat  has  brought  the  glass  into  a  soft  state,  it 
is  by  no  means  easy  so  exactly  to  turn  the  tube  at  both  ends 
alike,  and  so  lightly  yet  equally  to  hold  them,  that  the 
soft  part  shall  retain  its  cylindrical  shape  ;  being  neither 
twisted,  nor  bent,  nor  elongated,  nor  thrust  up.  Again, 
when  the  end  of  a  tube  is  heated  for  an  inch  or  more  at  once, 
or  when  a  tube  is  heated  so  near  the  end  that  it  cannot  be 
supported  there,  but  must  be  sustained  from  the  other  end, 
then  the  soft  glass  will  tend  by  its  weight  to  bend  downwards. 
This  must  be  counteracted  by  turning  round  the  tube  in  the 
hand,  so  as  continually  to  correct  the  inclination,  letting  the 
weight  of  the  soft  part  at  one  moment  rectify  the  bend  it  had 
received  the  instant  before.  During  this  practice,  it  should 
rather  .be  held  with  the  hot  end  inclining  upwards  than 
downwards,  the  latter  position  causing  the  tendency  of  the 
soft  piece  of  glass  to  draw  off  and  separate  from  the  remainder. 

1149.  In  this  kind  of  practices  is  included  that  of  retain- 
ing the  glass  steadily  in  one  particular  part  of  the  flame  at 
pleasure,  and  not  moving  it  by  uncertain  motions  of  the  hand 
from  place  to  place.     Very  little  experience  will  give  a  mode- 
rate degree  of  facility  in  these  operations,  and  will  enable  a 
student  to  make  his  apparatus  in  a  form  adapted  for  use. 
Every  fresh  trial  will  increase  his  facility  of  working,  and 
render  his  results  more  perfect. 

1150.  Work  of  this  kind  should  generally  be  performed  at 
or  towards  the  lower  surface  of  the  flame  (1143),  and  al- 
most always  be  removed  out  of  the  flame  downwards.     By 
this  arrangement  the  hottest  part  of  the  glass  is  constantly 
at,  or  towards,  the  top  of  the  tube,  so  that  it  may  be  seen; 
and  consequently  the  operations  whatever  they  may  be,  as 
sealing  apertures,  or  fastening  in  platinum  wire,  are  more 
conveniently  watched.     The  position  of  the  hottest  part  of 
the  tube  being  also  constant  and  known,  allows  of  an  advan- 
tage in  bending  or  forming  the  glass,  the  force  necessary 
being  applied  in   the  proper  direction  with   certainty  and 
readiness. 

1151.  When  the  glass  has  received  the  required  form,  it 
is  to  be  cooled;  this  must  be  effecte^f^fith  some  care.     It 
must  never  be  taken  directly  from  the  flame,  and  laid  on  cold 
bodies,  as  it  is  then  almost  sure  to  crack.     When  thin,  it  is 


518        GLASS  ROD  —  CUT  —  HEATED  —  FORMED. 

not  necessary  to  pay  much  attention  to  the  annealing,  but 
being  brought  to  the  end  of  the  flame  or  beyond  it,  and  there 
allowed  to  fall  below  a  red  heat,  it  may  afterwards  be  laid 
aside  on  a  tray  or  across  some  raised  body,  as  a  fragment  of 
tube,  that  the  hot  part  may  be  in  the  air.  But  if  the  glass 
be  large  or  thick,  it  then  requires  annealing;  for  which  pur- 
pose it  should  be  carried  slowly  from  the  hot  to  the  cooler 
parts  of  the  flame,  the  appearances  and  tints  being  watched, 
that  the  temperature  may  be  very  gradually  lowered;  and  it 
should  be  kept  for  several  minutes  in  the  stream  of  hot  air  be- 
yond the  flame  for  the  same  purpose,  being  gradually  carried  to 
the  less  heated  part  of  it,  and  ultimately  entirely  removed.  An 
instance  of  the  necessity  of  this  kind  of  annealing  has  been 
already  pointed  out  (967).  When  laid  aside,  it  is  advisable 
to  cover  the  cooling  glass  with  a  fold  or  two  of  paper  or 
cloth,  to  make  the  loss  of  temperature  still  more  gradual. 
These  precautions  are  the  more  necessary,  if  the  glass  varies 
in  thickness,  as  for  example,  at  the  junction  of  one  tube 
with  another,  or  at  the  end  of  a  tube  sealed  hermetically; 
and  they  are  equally  indispensable  with  the  irregularities 
resulting  from  the  awkward  form  of  a  bend,  the  fusion  of 
wires  into  glass,  or  other  circumstances. 

1152.  The  applications  of  these  general  directions  will  be 
best  understood  by  describing  some  of  the  more  directly 
useful  operations.  One  of  the  simplest  of  these  is  that  of 
forming  the  termination  of  a  piece  of  glass  rod  to  fit  it 
for  use  as  a  stirrer  (374).  The  piece  of  which  it  is  to  be 
formed  is  to  be  cut  of  a  proper  length.  For  this  purpose, 
a  deep  mark  is  to  be  made  round  the  rod  with  the  edge  of  a 
sharp  three-square  file,  and  being  then  grasped  by  the  two 
hands  placed  one  on  each  side  of  the  mark,  force  is  to  be 
applied  in  a  manner  similar  to  that  which  is  adopted  in  break- 
ing a  stick  in  two,  except  that  in  addition  the  hands  are  to 
pull  slightly  in  opposite  directions.  If  the  separation  be 
not  readily  effected,  the  file-mark  must  be  deepened.  Tubes 
are  cut  in  a  similar  manner  (128,  910);  such  as  are  small, 
without  difficulty  or  accident;  larger  ones  with  a  little  more 
care.* 


*  Rods  or  tubes,  less  than  half  an  inch  in  diameter,  are  most  neatly  broken 
across,  after  the  file  has  made  one  single  notch  on  one  side.     The  force  should  be 


GLASS  ROD  COMPLETED TUBE  BENT.          519 

| 

1153.  When  separated  by  the  file,  the  end  of  the  rod  is 
flatand  the  edges  are  sharp.     Being  heated  carefully  (1136), 
because  of  its  thickness,  beginning  at  a  little  distance  from 
the  extremity,  it  will  be  found  that  as  soon  as  the  glass  has 
attained  a  visible  hea^at  the  end,  the  sharp  angle  at  the 
edge  will  disappear,  yielding  to  the  cohesive  force  of  the 
particles  of  glass,  which  will  cause  the  end  to  assume  a  form 
more  or  less  approaching  to  roundness.     This  effect  being 
attained,  the  rod  is  to  be  annealed  for  a  short  time,  cooled 
carefully,  and  is  then  ready  for  use.     If  a  conical  termination 
be  required  (70),  then,  when  the  end  of  the  rod  is  hot  and 
soft,  the  extremity  of  a  fragment  of  glass  tube  should  be 
heated  and  pressed  against  it,  and   will  adhere.    The  rod 
should  then  be  moved  a  little,  so  that  the  greatest  heat  may 
be  given  at  a  tenth  or  twelfth  of  an  inch  from  the  end,  and 
then  by  withdrawing  the  fragment,  which  serves  as  a  handle, 
the  end  of  the  rod  will  be  drawn  away  with  it,  leaving  the 
termination  of  a  conical  form.     When  this  is  obtained,  the 
tail  of  glass  may  be  separated  from  what  is  to  be  the  blunt' 
apex  of  the  cone,  by  bringing  the  point  of  the  flame  upon 
it,  which  causes  the  thin  thread  to  fuse,  and  separate,  and 
the  portion  still  remaining  on  the  rod  to  run  together.     By 
retaining  the  end  of  the  rod  in  the  hot  flame,  the  extremity 
will  become  more  and  more  rounded;  but  when  the  desired 
form  is  acquired,  the  temperature  must  be  lowered  and  the 
glass  cooled  as  before  described  (1151). 

1154.  The  operation  next  in  simplicity  is  bending  a  tube, 
requisite  for  the  making  of  syphons,  tube  retorts,  and  for 
tube  operations  of  all  kinds.     An  unpractised  person  will 
effect  this  most  easily  with  a  piece  of  tube  about  six  or  seven 
inches  in  length,  half  an  inch  in  diameter,  and  the  twelfth 
or  fourteenth  of  an  inch  in  thickness.     Such  a  piece  is  easily 
handled,  retains  its  heat  longer  than  a  smaller  or  thinner 

applied  on  the  same  side  with  the  file-mark,  the  direction  of  the  movement  being 
towards  the  opposite  side.  Besides  the  greater  trouble  of  making  a  mark  around 
the  tube  or  rod,  there  is  less,  certainty  by  that  method,  of  forming  a  neat  and 
regular  fracture. 

By  using  a  wet  file  the  work  is  done  not  only  more  expeditiously  but  more 
safely.  This  is  more  obvious  when  the  end  of  a  tube  is  to  be  made  uniform  by 
rasping.— ED. 


520  GLASS  TUBE HEATED BENT. 

tube,  and  requiring  more  power  to  bend  it,  it  is  for 
that  reason  more  steady  in  the  hand.  Being  heated  in  the 
manner  already  described  (1134),  nothing  will  be  found 
more  easy  than  to  bend  it ;  but  if  this  be  done  hastily  or  inat- 
tentively, the  bend  will  be  of  a  bad  form;  contracted  in  its 
channel;  thin  in  one  part  and  thick  in  another;  probably 
wrinkled  and  distorted,  and  then  very  liable  to  crack  on 
cooling. 

1155.  To  avoid  these  errors,  when  the  glass  is  uniformly 
heated  for  the  length  of  half  an  inch  or  more,  and  to  such 
a  degree  that  it  is  manifestly  soft  by  the  feel,  it  should  be 
taken  out  of  the  flame ;  and  the  two  ends  being  now  simply 
inclined  in  oppositedirections,  but  without  any  other  tendency 
by  the  hand,  the  glass  is  to  be  bent  gradually  in  such  a  direc- 
tion that  the  convex  part  shall  be  towards  the  eye.     The  ope- 
ration should  be  continued  until  the  required  degree  of  curva- 
ture, or  the  desired  angle  formed  by  the  two  straight  parts  is 
attained,  or  until  the  glass  from  cooling  has  become  too  hard 
to  yield  ;  in  the  latter  case  it  must  be  re-heated,  and  the  ope- 
ration completed. 

1156.  The  heat  in  this  operation  should  be  nearly  uniform 
all  round  the  glass,  that  on  applying  force  the  parts  may 
give  way  together,  the  glass  at  the  convex  surface  being  ex- 
tended to  a  certain  degree,  and  drawn  out,  whilst  that  at  the 
concave  surface  is  equally  but  uniformly  thickened  by  its 
necessary  contraction  into  a  smaller  space.     If  the  glass  be 
much  hotter,  and  consequently  much  softer,  on  one  side  than 
the  other,  weakness  or  distortion  of  the  bend  usually  happens. 
For  if  the  hot  part  be  on  the  convex  side,  it  yields  during  the 
operation  much  more  than  the  stiffer  glass  on  the  cooler 
part,  which  consequently  undergoes  but  little  contraction, 
whilst  on  the  contrary  the  soft  glass  is  extended  considera- 
bly, rendered  very  thin,  and  usually  assumes  a  flattened  form 
or  if  the  hotter  part  be  on  the  concave  side  of  the  bend,  the 
cooler  and  convex  part  will  scarcely  extend  during  the  opera- 
tion, the  hot  glass  beneath  giving  way  to  the  force,  and  be- 
coming generally  thrust  up  into  a  sharp  fold  or  into  wrink- 
les ;  or  if  the  hotter  surface  be  on  one  side  of  the  bend,  then 
the  glass,  yielding  more  easily  on  one  side  than  the  other, 
usually  acquires  an  irregular  and  disturbed  form. 


GLASS  TUBE BENDING.  521 

1157.  On  the  whole  it  is  better  that  the  heat  should  be 
somewhat  greater  on  the  convex  than  on  the  concave  part, 
inasmuch  as,  though  it  yields  rather  more  than  it  ought,  it  is 
not  so  readily  formed  into  wrinkles,  and  also  because  it  cools 
more  rapidly  than  the  concave  side.     This  more  rapid  degree 
of  refrigeration  depends  upon  the  fact,  that  the  glass  on  the 
convex  side  becoming  extended  and  thinner,  consequently 
loses  heat  faster  than  the  concave  part,  which,  owing  to  con- 
traction during  the  operation,  becomes  thicker;  this  circum- 
stance may  therefore  be  compensated  by  a  little  extra  heat  at 
the  commencement. 

1158.  If  the  glass  be  too  hot,  it  gives  way  so  readily 
during  the  operation  as  to  assume  irregular  forms,  and  some- 
times, especially  in  sharp  bends,  becomes  flattened;  the  con- 
vex and  concave  sides  approaching  each  other,  and  the  lateral 
portions  extending  outwards.     This  particular  condition  is 
even  useful  occasionally,  as  it  prevents  the  necessity  of  great 
extension  or  contraction  of  the  glass  on  the  convex  or  concave 
surfaces;  but  an  irregular  and  wrinkled  bend  should  never 
purposely  be  allowed,  the  bore  of  the  tube  being  preserved 
nearly  as  round  and  free  there  as  elsewhere.     If  a  part  be 
observed  on  bending  to  lose  its  proper  form,  and  to  become 
flattened  or  wrinkled  into  folds,  from  the  heat  being  either 
too  great  or  irregular,  that  part  should  be  allowed  to  cool 
a  little,  whilst  the  heat  is  applied  to  the  neighbouring  portions, 
particularly  to  such  as,  by  contraction  on  the  concave,  or 
expansion  on  the  convex  sides,  during  the  continuance  of  the 
operation,  are  likely  to  rectify  the  irregularity  of  form  just 
commencing. 

1159.  Thin  and  small  tube  will  require  much  less  heat,  and 
generally  more  care,  than  that  which  is  thick  or  large;  but  it 
is  the  degree  of  softness  which,  indicated   by  the  feeling, 
must  principally  guide  the  operator  in  his  proceedings. 

1160.  When  a  considerable  bend  is  to  be  made,  the  angle 
formed  by  the  two  arms  being  very  small,  as  in  a  syphon  for 
instance,  it  should  not  be  effected  entirely  at  one  particular 
part  of  the  glass,  but  a  portion  having  been  heated  and  bent 

3  Q, 


522  BENDING  OF  GLASS — CARE  REQUIRED. 

as  far  as  possible,  without  weakening  or  distorting  the  tube  or 
contracting  the  bore,  the  neighbouring  parts  should  be  heated 
and  the  curvature  continued  until  the  desired  inclination  of 
the  two  arms  is  obtained.  Small  and  thick  tube  may  be  bent 
more  sharply  than  large  or  thin  tube,  the  latter  requiring 
greater  extent  of  curvature  for  the  preservation  of  the  proper 
form. 

1161.  When,  during  the  operation  of  bending,  different 
parts  are  to  be  heated  and  bent  in  succession,  it  is  best  to 
begin  the  operation  at  one  end  of  that  part  over  which  it  is  to 
extend,  and  gradually  proceed  from  it  to  the  other  end.     By 
thus  proceeding  the  operator  may  contrive,  when  one  part  is 
heated  and  ready  to  be  curved,  to  remove   it  sideways  from 
the  flame,  so  as  to  bring  the  next  portion  into  the  heat,  which 
will  then  be  acquiring  temperature  whilst  the  former  part  is 
bending,  and  in  consequence  of  its  previous  high   tempera- 
ture resulting  from  mere  vicinity  will  soon  be  in  a  properly 
heated  state.     This  transition,  as  it  were',  of  the  tube  through 
the  flame,  must  not  take  place  irregularly,  but  gradually,  the 
heating  and  bending  going  on  without  interruption,  and  over 
successive  portions  of  the  tube,  at  the  same  time*     A  clear 
idea  of  the  manner  in  which  this  is  to  be  done,  and  very  use- 
ful first  practice,  may  be  easily  acquired  by  using  a  spirit- 
lamp  flame  without  a  blow-pipe,  and  drawing  a  piece  of  quill 
tube  through  it  so  gradually,  that  the  part  in  the  flame  shall 
be  heated  red  hot  before   leaving  it.     It  will   then  be  found 
that  by  giving  lateral  pressure  on  one  end  of  the  tube  the 
parts  will  be  bent  and  curved  in  succession  as  they  become 
heated,  and  fixed  as  by  their  motion  onwards  they  become 
cooled. 

1162.  When  the  flexure  is   required  so  near  the  end  of  a 
piece  of  tube  as  to  render  it  impossible  to  hold  the  shorter  side 
with  the  fingers,  the  force  required  must  be  given  by  pressing 
against  the  end  with  a  piece  of  wood  or  another  piece  of  glass 
tube.     But  if  the  bend  is  to  be  continued  to  the  very  extre- 
mity, then  wood  or  glass  will  not  answer  the  purpose,  for  the 
first  would  burn  or  soil  the  tube,  and  the  last  melt  and  adhere 
to  the  heated  part. 


GLASS  MOULDED — CLOSING  TUBES.  523 

1163.  In  such  cases  cold  metal,  as  a  metallic  rod,  is  the 
best  adapted  for  use;  but  it  should  be  applied  only  at  the  mo- 
ment when  pressure  is  wanted,  and  never  be  retained  so  long 
in  contact  with  the  hot  glass  as  to  reduce  its  temperature  be- 
low the  point  of  softness;  for,  as  soon  as  the  glass  becomes 
solid,  the  cold  metal  would  crack  it.     For  the  same  reason, 
metal  should  not  be  used  in  the  cases  where  wood  and  glass 
have  just  been  recommended,  as  it  would  probably  crack 
the  hot  but  solid  part  of  the  glass.     Whenever  cold  metal 
is  brought  into  contact  with  glass  for  the  purpose  of  mould- 
ing or  working  it,  the  glass  should  be  hot,  and  not  be  allowed 
to  cool  to  its  point  of  hardness.     The  metal  itself  should 
always  be  cold  in  such  cases,  or  at  least  not  very  hot,  other- 
wise it  will  adhere  to  the  glass  and  cause  injury  ;  neither 
should  it  be  small,  like  a  wire,  lest  the  glass  itself  should 
communicate  so  much  heat  as  to    cause  its  adhesion.     If 
the  metal  be  hot,  and  the  glass  below  its  soft  point,  they 
may  be  brought  together  without    risk  of  fracture  to  the 
glass. 

1164.  Quill  tube,  as  has  been  already  remarked,   may  be 
bent  in  the  flame  of  a  spirit-lamp.     It  may  also  be  bent  over 
the  glass  of  an  argand  lamp  in  good  combustion.     Larger 
tubes  may  be  curved  over  acharcoal  fire,eitherln  the  crucible 
furnace  (157),  or    arranged  on    a  piece    of  metal    plate. 
Their  flexures  are  large  and  gradual,  not  so  short  and  sharp 
as  those  effected  by  the  lamp  and  blow-pipe.     Cooper's  lamp 
furnace  (7 1 0)  is  a  very  excellent  instrument  for  softening  con- 
siderable lengths  of  tubes  when  the  bend  required  is  to  be 
very  gradual  and  extensive.     The  tube  should  be  continually 
moved  in  the  flame,  both  with  a  lateral  and  rotary  motion, 
until  uniformly  heated  to  a  sufficient  degree. 

1 165.  The  next  operation  to  be  described  is  equally  useful 
with  the  last:  it  is  that  of  closing  the  extremities  of  tubes  so 
as  to  shut  up  one  end  and  form  those  useful  vessels  (127, 
9 1 0)  already  often  referred  to.   This  operation  is  most  readily 
performed  with  a  piece  of  straight  tube,  open  at  both  ends, 
and  long  enough  to  make  two  closed  tubes.     Let  it  be  there- 
fore supposed  that  a  piece  of  tube,  such  as  that  before  men- 


524  TUBES  CLOSED. 

tioned  (1154),  is  now  to  be  formed   into  two  tubes,  each 
closed  at  one  extremity. 

1 166.  The  piece  of  tube  is  first  to  be  heated  in  the  middle ; 
but  in  place  of  endeavouring  to  extend  the  heated  part  as 
far  as  possible,  it  should  rather  be  contracted  into  a  narrow 
ring  (1 141).     The  hands  are  then  to  be  separated,  the  glass 
being  pulled  in  the  direction  of  its  length,  when  it  will  be 
found  to  elongate,  and  at  the  same  time  contract  in  diameter 
at  the  hot  and  soft  part.     Some  degree  of  management  in  the 
fieat  is  now  required.     If  it  were  still  to  be  urged  upon  the 
middle  of  the  contraction,  and  the  pulling  force  also  conti- 
nued, the  tube  would  suddenly  be  divided  into  two  parts  with 
irregular,  long,  and  pointed  terminations.     For  as  the  glass 
is  drawn  out,  and  the  diameter  as  well  as  thickness  diminish- 
ed, the  flame  acts  upon  it  as  if  it  were  a  smaller  tube ;  the 
smallest  part  is  consequently  always  hottest,  it  yields  most 
readily  to  the  force  applied,  and  thus  the  hasty  and  imper- 
fect result  mentioned  would  be  obtained.  If  on  the  contrary, 
to  avoid  this,  the  glass  were  moved  so  that  the  flame  fell  upon 
and  heated  the  portions  at  the  side,  then  their  softness  might 
be  made  to  surpass  that  of  the  contracted  part  of  the  tube, 
and  the  pulling  would  merely  tend  to  elongate  and  contract 
this  part  also,  and  so  to  reduce  the  whole  of  the  tube  to  por- 
tions of  tube  of  greater  length,  but  smaller  diameter. 

1 167.  It  is  an  effect  between  these  that  the  operator  should 
produce.     As  soon  as  the  glass  yields  to  the  pull,  and  in  pro- 
portion as  the  diameter  diminishes,  he  should  relax  the  force 
so  as  to  apportion  it  to  the  softness  of  the  glass,  and  proceed 
gradually  with  the  operation;  he  should  at  the  same  time 
move  the  glass  towards  the  extremity  of  the  flame,  and  even 
out  of  it,  that  he  may  be  able  to  moderate  the  heat  and  apply 
it  principally  to  a  small  surface.     He  should  no  longer  en- 
deavour to  keep  the  two  pieces  of  glass  of  equal  form,  but 
using  one  as  an  adjunct,  turn  all  his  attention  to  finishing  the 
extremity  of  the  other,  which  probably  will  be  that  in  his 
left  hand,  because  the  piece  in  his  right  hand  becomes  the 
tool  with  which  he  works,  and  which   is  thus  most  adroitly 
used.     Directing  therefore  the   point  of  the  flame   upon 


TUBES  CLOSED — PROGRESS.  525 

what  is  to  be  the  bottom  of  the 
closed  tube,  a  little  above   the 
thinnest    part,   but   still  not   so 
/a  much   above  as    to  render   the 

thicker  part  the  softest,  let  him 
carefully  retract  his  right  hand, 
by  which  operation  the  narrow 
part  will  become  more  and  more 
attenuated,  and  finally,  when 
capillary,  fuse  and  separate.  The 

end  of  the  tube  will  be  left  closed  of  a  round  form,  with  pro- 
bably a  little  knob  of  glass  at  the  middle  of  the  bottom, 
whilst  the  other  piece  will  be  drawn  out  rather  irregularly, 
though  closed  also  at  its  extremity.  The  accompanying  wood- 
cut illustrates  the  successive  changes  in  the  form  and  appear- 
ance of  the  tube ;  the  part  to  which  the  greatest  heat  should 
be  applied,  being  pointed  out  by  the  lines  a  a  a. 

1168.  The  tube  is  seldom  perfectly  finished  by  this  opera- 
tion. To  complete  it,  the  knob  of  glass  at  the  end,  if  small, 
and  the  whole  of  the  bottom  of  the  tube,  should  be  heated 
until  the  glass  is  soft.  Then  applying  the  open  end  of  the 
tube  to  the  mouth,  and  propelling  air  into  it  with  a  degree 
of  force  proportionate  to  the  heat  of  the  glass,  it  will  yield 
(1194),  the  knob  expanding  more  than  any  other  part,  be- 
cause of  its  higher  temperature,  and  of  its  continuing  for  a 
greater  length  of  time  in  a  soft  state.  In  this  manner,  by  a 
little  address,  the  knob  may  be  made  to  disappear,  and  the 
bottom  of  the  tube  to  assume  a  regular  round  form  (127,  142), 
and  a  thickness  nearly  equal  in  every  part  (1198). 

1 169.  If  the  knob  be  so  large  and  clumsy,  in  consequence 
of  the  partial  failure  of  the  first  operation,  that  if  heated  so 
as  to  run  up  and  make  part  of  the  bottom  of  the  tube,  it  would 
cause  the  formation  of  a  very  thick  portion  of  glass  there, 
then  it  must  be  removed.  For  this  purpose  it  is  to  be  heated, 
and  a  piece  of  waste  glass,  previously  warmed  in  another 
part  of  the  flame  while  held  in  the  right  hand,  applied  to  it: 
then  directing  the  point  of  the  flame  above  the  junction  and 
against  the  part  intended  for  the  bottom  of  the  tube,  the 
glass  should  be  melted,  the  thick  clumsy  knob  drawn  off, 


526  TUBE  FULLtf  CLOSED. 

and  a  fresh  closing  of  the  tube  effected  and  finished  as  be- 
fore. Or  if  from  want  of  practice  the  end  of  the  tube  be 
irregular,  misshapen,  and  altogether  bad,  then  after  attach- 
ing the  piece  of  waste  tube,  which  serves  as  a  tool,  the  heat  is 
to  be  applied  a  little  way  up  the  tube,  the  glass  softened  in 
another  place  as  near  to  the  first  as  possible,  and  the  opera- 
tion recommenced  ;  the  piece  of  glass  at  the  end  being  drawn 
off  and  managed  by  means  of  the  fragment  of  tube  which 
had  been  attached  to  it  for  the  occasion.* 

1170.  If  the  end  of  the  tube  when  finished  be  thin,  it 
should  be  raised  to  a  red  heat,  with  a  little  of  the  neighbour- 
ing thicker  part,  when  it  will  gradually  contract  and  thicken, 
and  it  may  thus  be  made  of  equal  strength  with  the  sides  of 
the  tube.     Its  thickness  must  be  judged  of  by  inspection,  in 
the  manner  formerly  described  (372).     On  the  contrary,  if 
it  be  too  thick,  it  may  be  rendered  thinner  by  being  blown 
out  as  mentioned  above  (1168).     The  precautions  requisite 
in  doing  so  will  be  immediately  described  (1194,  1198). 

1171.  Having  finished  one  of  the  tubes  to  be  formed  out  of 
the  original  piece,  the  other  which  had  been  laid  down  is  to 
be  resumed  and  completed.     For  this  purpose,  when  held 
in  the  left  hand,  the  point  of  the  flame  is  to  be  directed  as 
before  mentioned  upon  that  part  of  the  contracted  termina- 
tion, which  is  to  form  the  bottom  of  the  tube,  and  when  soft 
the  tail  of  glass  is  to  be  drawn  off  in  the  manner  just  de- 
scribed for  removing  a  knob  (1169).     The  tube  is  then  to 
be  finished  according  to  the  directions  already  given  (1 168). 

1172.  When  the  piece  of  tube  to  be  operated  with  is  thin, 
the  extent  of  surface  heated  at  first  must  be  greater,  and  the 
operation  carried  on  more  carefully,  than  is  necessary  with 
thicker  tube.     For  if  a  small  extent  only  be  heated,  and  then 
drawn  out  quickly,  the  glass  becomes  so  attenuated,  that 
when  very  hot  it  will  of  itself  run  into  holes,  or  if  it  remain 
undivided,  will  form  a  bottom  to  the  tube,  so  thin  that  it  will 
not  be  safe  to  trust  such  a  vessel  for  an  experiment,  lest  a 
slight  concussion  should  break  it.     In  this  case,  after  the 

*  The  speediest  way  of  getting  rid  of  a  solid  button  at  the  end  of  a  closed  tube 
is  to  cut  it  off  when  red  hot,  with  scissors.  A  very  slight  inflation  will  then 
round  off  the  sealed  extremity. — ED. 


THIN  TUBES  CLOSED THICKENED.  527 

tube  is  partly  drawn  out  and  its  diameter  contracted,  the 
heat  should  be  raised  considerably  but  uniformly  round  the 
thin  narrow  part,  and  the  glass,  being  retained  in  an  undis- 
turbed state,  should  be  allowed  to  draw  together  and  thicken 
(1179).  When  that  has  taken  place  to  a  sufficient  degree, 
it  is  again  to  be  drawn  out,  and  if  a  second  time  it  become 
too  thin,  it  must  be  thickened  as  before:  in  this  manner  the 
operation  must  proceed,  until  the  bottom  is  closed  and  com- 
pleted. 

1 173.  When  a  piece  of  tube  is  too  short  to  be  formed  into 
two  tubes,  it  must  be  sealed  at  one  extremity — an  operation 
often  required  for  other  purposes.     In  these  cases  the  end 
to  be  sealed  must  be  heated  carefully  (1 137),  the  tube  being 
inclined  a  little  with  the  heated  aperture  towards  the  direc- 
tion of  the  course  of  the  flame,  that  the  force  of  the  blast 
may  not  throw  hot  air  into  and  along  it,  and  burn  the  hand 
at  the  other  extremity;   and   in  some  cases  also  that  the 
products  of  the  combustion  may  be  prevented  from  entering 
the  tube  and  affecting  the  substances  already  placed  within 
it  (1 184).     When  the  end  is  soft,  a  piece  of  waste  glass  tube 
is  to  be  held  in  the  right  hand,  and  its  extremity  used  to 
press  the  sides  of  the  hot  end  together,  and  when  three  or 
four  places  on  the  edge  have  been  thus  made  to  approach 
each  other,  the  end  of  the  spare  tube  is  to  be  attached  to 
them,  and  the  heat  being  raised  a  little  above  the  termina- 
tion, the  piece  is  to  be  drawn  off  and  the  operation  proceeded 
with  exactly  in  the  manner  already  described  (1167,  1 169). 

1 174.  When  a  piece  of  tube  is  too  short  to  be  held  by  the 
fingers  during  the  operation  because  of  the  heat,  a  cork, 
square  or  of  irregular  form,  that  it  may  not  close  the  tube 
perfectly,  should  be  put  into  the  mouth  to  serve  for  a  handle, 
by  which  it  may  be  conveniently  held  (918);  even  a  plug  of 
paper  or  a  piece  of  wood  will  answer  the  same  purpose. 

1 175.  The  information  given  relative  to  glass-blowing  will 
enable  the  student  to. make  much  of  the  apparatus  already 
referred  to.     Tube  retorts  (924)  are  made  by  first  closing 
the  end  of  a  piece  of  tube,  and  then  the  parts  representing 
the  body  and  the  neck  are  to  be  separated  by  a  bend  more  or 
less  sharp,  according  to  the  intended  application  of  the  vessel. 


528  MAKING  SYPHONS  AND  CAPILLARY  TUBES. 

In  the  same  manner  are  the  tubes  necessary  for  the  conden- 
sation of  gases  to  be  made  (962).  Syphons  (550)  are  made 
merely  by  bending  glass  tube;  or  if  their  apertures  are  to  be 
contracted,  the  proceeding  is  the  same  as  that  necessary  in 
the  first  part  of  the  process  for  closing  a  tube  (1 167),  the  ope- 
ration being  carried  no  farther  than  to  lessen  the  diameter: 
that  done,  the  glass  is  to  be  allowed  to  cool,  and  the  narrow 
part  is  then  to  be  cut  by  a  file  (1152). 

1176.  If  when  the  glass  tube  is  heated  all  round  and  much 
softened,  the  parts  be  pulled  asunder  quickly,  and  not  in  the 
guarded  manner  already  advised,  then  instead  of  a  mere  con- 
traction of  a  small  portion  of  the  tube  to  two-thirds  or  one- 
half  its  first  diameter,  it  will  become  extended  and  capillary; 
and  the  two  portions  of  the  tube  held   by  the  fingers,  thus 
connected,  will   be  found  to  contract  in  diameter  for  the 
space  of  half  an  inch  or  an  inch,  gradually  becoming  capil- 
lary.    This  operation  is  frequently  useful  in  the  preparation 
of  capillary  tubes  for  various  purposes,  as  in  the  contraction 
and  elongation  of  the  ends  of  glass  retorts  or  other  similar 
apparatus  (463,  559);  and  in  making  tube  funnels  (924), 
syringes,  (560),  &c.     It  should  always  be  performed  in  the 
air,  and  not  in  the  flame  of  the  lamp,  unless  the  operator  be 
very  expert :  when  the  glass  therefore  is  heated,  it  is  to  be 
removed  from  the  flame  and  drawn  out. 

1177.  The  greater  the  heated  portion  of  glass,  the  longer 
will  be  the  tube  thus  formed.     Its  length  and  fineness  also 
increase  with  the  rapidity  with  which  it  is  drawn,  and  with 
the  temperature  given  to  it  in  the  first  instance.     The  velo- 
city with  which  the  hands  should  separate  is  most  generally 
useful  at  the  rate  of  about  a  foot  in  a  second.     The  thick- 
ness, length,  and  general  character  of  the  capillary  tube 
produced  is  also  considerably  dependant  on  the  kind  of  tube 
out  of  which  it  is  made :  the  relation  of  the  diameter  to  the 
thickness  of  the  glass  will  be  nearly  the  same  in  the  tube 
both  before  and  after  it  is  drawn  out. 

1178.  When  a  contracted  tube  is  required  too  long  to  be 
made  at  once,  then  having  drawn  one  length,  the  original 
tube  is  again  to  be  heated  so  near  to  the  part  already  drawn, 
that,  when  extended,  only  a  little  swelling  or  bulb  may  in- 


CAPILLARY  TUBES TUBE-FUNNELS.  523 

fervene  between  the  capillary  portions.  It  is  not  safe  to 
endeavour  to  heat  the  tube  so  near  to  the  already  extended 
part,  as  on  drawing  it  out,  to  make  one  tube  with  the  latter 
without  irregularity;  for,  owing  to  its  delicacy,  the  pre- 
viously extended  part  will  almost  certainly  give  way  :  no 
difficulty  occurs  in  afterwards  softening  and  drawing  down 
the  small  expansions ;  for  by  making  use  of  a  little  spirit- 
lamp  flame  (205),  placed  under  the  bulbs,  they  are  soon^ 
raised  to  a  red  heat,  and  then  by  careful  management  are 
easily  drawn  down. 

1179.  When  the  ends  of  retorts  or  other  tube  apparatus 
are  to  be  thus  reduced  in  diameter  (463),  they  should  not 
be  drawn  out  more  than  is  necessary,  but  left  with  sufficient 
strength  to  resist  the  slight  mechanical  accidents  to  which 
they  are  liable  in  the  course  of  experiments.     The  same 
remark  applies  to  such  vessels  as  the  small  receivers  or  re- 
tainers recommended  for  scarce  fluids  (92§).     If  the  neck 
of  the  retort,  or  tube,  to  be  drawn  out  be  thin,  it  is  for  the 
same  reason  advantageous  to  thicken  the  part  before  it  is 
extended  (1172);  for  which  purpose  the  glass  must  be  soft- 
ened in  the  flame,  and  retained  at  a  high  temperature  for 
some  time,  and  rather  thrust  together  than  pulled  out ;  in 
this  manner  the  thickness  of  the  glass  may  be  nearly  doubled, 
and  consequently  the  capillary  tube  resulting  from  its  linear 
extension  rendered  stronger. 

1180.  When  capillary  tubes   are  drawn  for  air-guages 
(1369),  several  should  be  made  of  different  diameters,  thick- 
nesses, and  lengths;  and  the  most  advantageous  afterwards 
selected. 

1181.  The  same  proceeding,  with  slight  variations,  is  suf- 
ficient for  the  production  of  several  kinds  of  useful  apparatus. 
A  tube  funnel  (924)  is  made  by  elongating  a  piece  of  tube 
in  this  manner,  at  about  an  inch  from  the  end,  and  then 
separating   it,  leaving   the   short   piece  with    so  much  of 
the  capillary   tube  attached   to  it   as  will  form   a  funnel 
of  sufficient  length.     Tube  syringes  of  various  kinds,  for 
the    removal    of    azotane,   washing    of   precipitates,   &c. 
(547,  560),  and  the  tubes  recommended  as  being  useful  in 
estimating  volumes  and  in  measuring  (130,  139),  are  made 

3R 


530  SYRINGES SEALING  OF  TUBES. 

with  equal  facility.  When  the  end  of  a  piece  of  tube  is 
heated  and  drawn  out,  a  form  more  or  less  acute  may  be 
given  to  the  termination,  which  being  cut  so  as  to  leave  an 
aperture  of  the  proper  size,  is  only  to  be  held  for  a  moment 
in  the  flame  to  soften  and  obliterate  the  edges  (1153),  and 
a  very  good  syringe  bpdy  is  formed.  A  little  tow  wrapped 
round  the  end  of  a  wire  and  moistened,  forms  an  effectual 
piston,  and  thus  an  instrument  of  great  use  in  numerous 
operations  is  quickly  made.  If  it  be  required  that  the 
termination  of  the  syringe  should  pass  off  obliquely,  it  is 
effected  by  drawing  out  the  tube  in  that  direction  when  hot. 

1182.  In  the  same  manner  the  separator  delineated  (559) 
is  made,  by  drawing  off  the  end  of  a  piecre  of  tube,  so  as  to 
form  a  moderately  stout  capillary  continuation,  and  then 
bending  this  upwards  as  in  the  figure.     The  gas  tube,  for 
conveying  products  into  small  tube  receivers  (448,  463),  is 
made  by  drawing  out  the  end  of  a  tube  until  of  capillary  di- 
mensions, and  then  bending  it  downwards. 

1183.  It  is  very  frequently  necessary  with  tube  apparatus, 
to  seal  apertures  hermetically,  so  as  entirely  to  close  the  ves- 
sel, and  make  it  continuous  in  every  part.     This  process  re- 
sembles that  by  which  one  end  of  an  open  tube  is  sealed 
(1173),  so  far  as  regards  softening  the  glass,  bringing  it  to- 
gether,  contracting  the  aperture,  and  ultimately  closing  it; 
but  it  differs  very  much  in  other  circumstances,  dependant 
upon  the  state  of  the  interior  of  the  vessel.     In  the  open  tube 
the  glass  is  equally  pressed  on  both  sides;  but  that  is  rarely 
the  case  in  the  closed  tube,  a  tendency  of  the  contents  to 
pass  outwards,  or  of  the  air  inwards,  almost  always  occurring. 

1184.  The  simplest  case  of  the  kind  is,  where  solid  fixed 
matter  is  to  be  confined  in  a  tube  for  the  purpose  of  preserv- 
ing it,  in  the  manner  already  spoken  of  (974).     The  included 
substance  then  sends  off  no  vapour,  and  all  that  is  to  be 
guarded  against  is,  the  expansion  and  contraction  of  the  air 
within  by  the  variations  of  temperature.     Suppose  the  tube 
closed  at  one  extremity,  and  that  one-half  or  two-thirds  of  it 
is  filled  with  the  substance;  care  should  be  taken  that  the 
latter  does  not  rise  so  near  to  the  upper  part  of  the  tube  as 
to  be  affected  by  the  heat,  especially  if  it  be  an  easily  fusible 


TUBES  SEALED DRAWN  OUT — CLOSED.  531 

or  changeable  body.  The  top  of  the  tube  when  brought 
towards  the  flame  should  be  inclined  (1173),  that  the  pro- 
ducts of  the  combustion  may  not  enter  it;  and  the  bottom 
should  be  inclined  downwards,  that  the  contents  may  not  fall 
towards  the  heated  part.  The  upper  part,  being  heated, 
should  be  drawn  out  and  contracted,  precisely  as  if  it  were 
the  end  of  an  open  tube  that  was  to  be  closed,  except  that 
the  glass  generally  should  be  retained  as  thick  (1172)  as  it 
will  be  required  when  finished,  in  order  that  the  capillary 
tube  may  be  of  considerable  comparative  thickness,  and  that 
an  aperture  for  the  air  through  the  middle  of  it  may  be  pre- 
served the  whole  time.  The  wood- 
cut will  illustrate  this  state  of  the 
tube.  No  difficulty  will  be  found 
in  directing  the  heat  about  a,  in 
drawing  off  the  end  piece,  and  in  leaving  the  tube  sealed, 
for  the  glass  will  readily  coalesce  at  the  moment  of  separa- 
tion; but  the  object  is  to  make  this  end  as  strong  as  any 
other  part  of  the  tube,  and  of  a  form  similar  to  that  of  the 
opposite  extremity;  for  effecting  this, the  following  explana- 
tions and  precautions  will  be  found  useful. 

1185.  Supposing  the  piece  drawn  off  and  the  end  closed  ; 
the  glass  is  so  hot  and  soft  at  the  moment,  that  if  from  an 
accidental  contact  of  the  flame  any  part  of  the  tube  becomes 
hotter  than  before,  the  air  within  will  expand,  the  glass  will 
be  blown  out  into  a  thin  bubble,  which,  breaking  even  by  the 
mere  pressure  of  the  atmosphere  as  the  tube  cools,  will  leave 
a  large  hole.     It  will  now  be  more  difficult  to  close  the  tube 
than  before  the  extremity  was  removed,  for  the  sides  of  the 
aperture  must  again  be  collected  together  and  drawn  off,  and 
a  capillary  neck  again  formed. 

1186.  This  may  be  avoided  by  purposely  heating  the  up- 
per part  of  the  tube  just  before  sealing  it  hermetically,  so  as 
to  expand  and  expel  the  air  from  within  ;  then,  removing  the 
flame  and  applying  it  to  the  capillary  neck  as  the  general 
temperature  of  the  tube  sinks,  the  piece  is  to  be  drawn  off, 
and  the  aperture  sealed,  and  as  the  pressure  is  inwards  rather 
than  outwards,  the  glass  will  be  pressed  in  the  former  direc- 
tion.    This  is  in  fact  the  method  to  seal  the  tube  strongly, 


532  SEALING  OF  TUBES — CASUALTIES. 

and  to  make  it  of  a  desirable  shape,  but  it  is  subject  to  an 
accident,  which  to  be  avoided  must  be  known.  If  the  glass 
at  the  end  has  been  left  thin,  and  it  be  heated  until  perfectly 
soft,  the  pressure  of  the  external  air  will  frequently  force  it 
inwards,  sometimes  into  a  decided  bubble,  or  else  into  vari- 
ous wrinkled  and  irregular  forms,  which,  when  cold,  are  al- 
most sure  to  crack  in  numerous  directions. 

1187.  These  accidents  are  avoided  by  making  the  end  o.f 
the  glass  and  the  capillary  neck  of  considerable  comparative 
thickness,  which  is  done  by  allowing  the  glass  to  gather  it- 
self up  when  in  a  fluid  state  (1172,  1179),  and  also  when 
warming  the  tube  to  expel  a  part  of  the  air,  by  not  raising  the 
temperature  too  much  ;  then,  upon  proceeding  to  soften  the 
neck  and  seal  the  extremity,  the  flame  should  be  directed  ra- 
ther generally  .to  that  end  of  the  tube  in  such  a  manner,  that, 
the  whole  being  softened,  the  apex  shall  still  be  retained  at 
the  highest  temperature.  In  this  way  it  will  be  easy  by  a 
little  practice  to  make  the  external  pressure  effectual  in  forc- 
ing in  the  end  of  the  glass  generally,  and  causing  it  to  be- 
come altogether  thicker  and  stronger,  instead  of  having  a 
small  portion  suddenly  blown  inwards,  and  the  whole  ren- 
dered irregular.  Or  if  by  too  long  a  continuance  of  heat, 
the  air  within  begins  to  expand,  still,  as  all  the  glass  at  the 
end  is  of  equal  softness,  the  whole  will  gradually  enlarge  out- 
wards; an  effect  which  vyill  be  immediately  perceived,  and 
the  operation  may  be  stopped  before  any  injury  is  occasioned. 

1183-  When  the  tube  contains  a  fluid  instead  of  a  solid 
body,  the  care  required  is  greater,  and  must  be  proportionate 
to  the  volatility  of  the  substance,  A  fixed  fluid,  if  alone, 
merely  requires  to  be  retained  in  the  lower  and  colder  part 
of  the  tube,  away  from  the  end  to  be  sealed.  Sudden  motion 
should  be  avoided,  lest  drops  be  thrown  upon  the  cold  part, 
and  cracks  be  occasioned :  during  cooling,  the  tube  should 
also  be  placed  steadily  with  its  heated  end  uppermost  (930). 
There  are  particular  cases  in  which  great  care  is  necessary 
to  prevent  disturbance  of  the  contents  of  the  tube.  Such  are 
the  experiments  upon  the  condensation  of  gases  (962),  in 
which  the  strength,  uniformity,  and  annealed  state  of  the  end 
hermetically  sealed,  are  essentially  necessary. 


VOLATILE  SUBSTANCES  CONFINED  IN  TUBES.       533 

1189.  If  the  substances  to  be  confined  are  volatile,  but 
yet  like  alcohol,  ether,  chloride  of  sulphur,  &,c.,  have  their 
boiling  points  not  lower  than  100°  or  150°,  then  additional 
precautions  will  be  needful :  these  apply  particularly  to  the 
moment  when  the  capillary  neck  is  to  be  finally  drawn  off  and 
closed,  and  the  end  thickened  and  made  strong.     The  effect 
of  heat  upon  tubes  with  such  contents,  is  not  only  to  expand 
the  air  within  them,  but  also  to  increase  its  bulk,  by  raising 
and  mixing  with  it  the  vapour  of  the  substance.     The  forma- 
tion of  this  vapour,  and  consequently  the  tendency  of  the 
gaseous  matter  within  to  expand,  is  not  simply  in  proportion 
to  the  heat  of  the  end  of  the  glass  tube  with  which  the  va- 
pour is  in  contact,  but  depends  also  upon  the  heat  communi- 
cated to  the  fluid  beneath.     This  effect  is  produced  more 
slowly  than  the  former,  and  may,  in  the  hands  of  an  inexpe- 
rienced person,  lead  to  confusion.     The  temperature  of  the 
glass  near  the  end  may  be  actually  falling,  and  may  lead  to 
the  expectation  of  a  diminution  in  bulk  of  the  gaseous  or  va- 
porous matter  within,  and  consequently  of  a  pressure  from 
without  inwards,  whilst  at  the  same  time  the  temperature  of 
the  fluid  may  be  rising  by  contact  with  the  neighbouring  hot 
or  warm  glass,  and  may  cause  an  increase  in  the  quantity  of 
vapour  given  off,  and,  upon  the  whole,  a  tendency  of  gase- 
ous matter  to  pass  out  of  the  tube;  which  not  being  antici- 
pated would  spoil  an  experiment  (930).     In  these  cases  the 
upper  part  of  the  glass  (1186)  should  be  heated  so  as  to  ex- 
pand the  gaseous  contents  a  little,  and  at  the  moment  the  ca- 
pillary neck  is  drawn  off,  and  the  aperture  closed,  a  piece  of 
moistened  bibulous  paper  should  be  applied  round  the  part 
of  the  tube  containing  the  fluid,  and  if  the  substance  be  very 
volatile,  even  a  little  higher  up,  though  not  to  the  heated 
part  of  the  glass.     This  will  prevent  any  further  elevation  of 
temperature  in  the  fluid,  and  the  end  may  be  safely  heated 
and  thickened  (1185),  in  the  manner  already  described  for 
tubes  containing  solid  bodies. 

1 190.  When  the  aperture  to  be  sealed  is  small,  and  at  the 
end  of  a  capillary  tube,  as  in  the  vessels  described  (929,  934, 
935),  nothing  more  is  required  than  to  hold  it  in  the  flame  of 
a  lamp  or  candle,  when  the  glass  will  fuse  and  coalesce.    Or 


534  INCLOSING  VOLATILE  MATTER. 

if  the  end  be  broken  and  rather  wide,  the  part  Softened  by 
heat  should  be  touched  with  another  piece  of  glass,  and  be 
drawn  out  and  sealed  as  before  ( 1 184).  In  these  cases  when 
sealed,  the  glass  is  to  be  removed  from  the  flame,  and  not 
suffered  to  run  into  a  little  ball,  which  would  generally  break 
off  when  cold,  or  after  an  interval  of  three  or  four  days. 

1191.  When  substances  so  volatile  as  to  boil  almost  at 
common  temperatures  are  to  be  sealed  up,  the  tubes  con- 
taining  them   must   be  cooled    by  refrigerating   mixtures. 
This  precaution  has  been  described  as  it  respects  sulphurous 
acid,  and  the  description  will  illustrate  the  process  for  similar 
substances  (930).     The  only  additional  remark  here  neces- 
sary is,  that  if  the  fluids  are  to  be  preserved  as  specimens, 
the  capillary  neck  should  be  of  considerable  thickness,  and 
when  effectually  sealed,  whilst  the  tube  is  in  the  frigorific 
mixture,  should  not  afterwards  be  altered,  nor  should  any 
attempt  be  made  to  give  it  more  thickness,  or  a  better  form. 
A  spirit  lamp  and  mouth  blow-pipe  is  more  convenient  for 
softening  the  capillary  necks,  and  sealing  these  tubes,  than 
the  table  blow-pipe. 

1192.  When  the  object  is  merely  to  close  the  ends  of 
capillary  tubes  (929),  it  is  easily  effected,  the  tubes  being 
cooled  at  the  same  time.     When  the  fluids  are  of  such  vola- 
tility as  to  cause  only  a  feeble  stream  of  vapour  from  the 
aperture  of  the  vessel   (and   several    such  may   be   found 
amongst  the  substances  held  in  vapour  in  oil  gas),  the  cohe- 
sive force  of  glass  is  sufficient  to  cause  it  to  run  together 
when  softened,  and  to  seal  the  orifice,  even  though  there  be 
a  slight  pressure  outwards.     For  this  purpose  the  end  of  the 

^capillary  tube  is  to  be  introduced  into  the  flame,  and  being 
touched  with  another  piece  of  glass,  the  extremity  is  to  be 
drawn  off,  and  at  the  same  time  sealed:  at  the  instant  of 
doing  this  it  is  to  be  removed  from  the  flame,  that  it  may 
cool  and  solidify,  lest  the  heat  of  the  lamp  or  hand  should 
increase  the  tension  of  the  vapour,  and  cause  such  pressure 
outwards  as  would  be  sufficient  to  expand  the  soft  glass. 

1193.  The  process  of  sealing  tubes  hermetically,  which 
have  been  previously  exhausted  of  air,  requires  certain  pre- 
cautions to  prevent  the  pressure  of  the  atmosphere  frorp 


EXHAUSTED  TUBES  SEALE1>  HERMETICALLY.  535 

either  making  an  entrance,  or  forcing  in  the  glass.  Suppose 
it  were  necessary  to  enclose  some  camphor  hermetically  in 
a  tube  exhausted  of  air,  that  certain. of  its  habitudes  as  to 
vaporization  arid  crystallization  under  such  circumstances 
might  be  observed.  A  tube  of  sufficient  length  is  to  be 
selected,  and  being  closed  at  one  end,  the  camphor  is  to  be 
introduced;  the  tube  should  then  be  heated  at  about  an  inch 
from  the  open  extremity,  and  should  be  contracted  and 
thickened  in  the  manner  described  (1172,  1184),  so  that  the 
smallest  part  may  be  about  half  an  inch  in  length,  about 
one-twelfth  of  an  inch  in  internal  diameter,  and  one-third 
of  an  inch  in  external  diameter.  A  retort  cap  is  to  be 
cemented  upon  the  open  extremity  (834),  and  a  stop-cock 
attached  to  it.  This  being  done,  the  tube  is  to  be  connected 
with  the  air-pump  and  exhausted,  and  the  stop-cock  being 
closed,  the  tube  is  to  be  removed  from  the  pump  in  its  ex- 
hausted state.  The  small  flame  of  a  spirit-lamp  is  now  to  be 
applied  to  the  middle  of  the  capillary  part,  so  as  to  heat  it 
gradually  all  round;  as  the  glass  softens  the  pressure  of  the 
atmosphere  will  make  it  collapse  and  become  solid,  the  pas- 
sage will  be  obliterated,  and  the  tube  will  be  converted  into 
a  rod.  This  done,  the  heat  is  to  be  applied  more  imme- 
diately to  the  middle  of  the  solidified  part,  which,  when  it 
has  become  soft,  is  to  be  drawn  asunder.  No  difficulty  will 
be  fqund  in  doing  this,  without  letting  in  the  smallest  por- 
tion of  air,  and  if  proof  of  the  accuracy  of  the  process  be 
required,  it  may  be  obtained  to  a  certain  degree  by  plunging 
the  piece  attached  to  the  stop-cock  under  water,  and  break- 
ing off  the  point  there;  if  the  water  should  enter  in  such 
abundance  as  to  fill  this  piece,  it  will  show  that  no  common 
air  has  entered  by  the  stop-cock,  and  the  appearances  will 
sufficiently  indicate  whether  air  has  entered  or  not  at  the 
part  heated.  No  attempt  should  be  made  to  thicken,  or  in 
any  way  bring  into  form,  the  sealed  end  of  the  exhausted 
tube;  for  the  pressure  of  the  air  will  be  almost  certain  to 
force  in  the  softened  glass,  unless  the  operator  be  indeed 
very  skilful. 

1194.  A  more  delicate  operation  than  any  yet  described, 
and  one  that  requires  considerable  practice  for  its  perform- 


536  BLOWIiNG  OF  BULBS. 

ance  with  even  moderate  success,  is  the  blowing  of  bulbs 
and  other  expansions,  either  in  the  middle  or  at  the  end  of 
a  tube.  Facility  will  be  best  obtained  by  practising  with  a 
piece  of  tube  about  nine  or  ten  inches  in  length,  one-third 
of  an  inch  in  diameter  externally,  and  one-tenth  of  an  inch 
in  internal  diameter.  The  end  is  first  to  be  closed;  and 
then  about  two-thirds  of  an  inch  in  length  of  the  closed  ex- 
tremity is  to  be  uniformly  heated,  until  so  soft  as  to  bend 
from  side  to  side  by  its  own  weight.  The  aperture  is  im- 
mediately to  be  placed  between  the  lips,  and  by  means  of 
the  mouth  (222,  &c.),  air  is  to  be  propelled  for  the  purpose 
of  expanding  the  soft  glass.  This  must  be  done  quickly  but 
cautiously;  and  as  soon  as  the  eye,  which  must  be  constantly 
fixed  upon  the  heated  end,  perceives  enlargement  there,  the 
force  exerted  by  the  mouth  should  be  slightly  diminished, 
and  the  operator  should  hold  himself  ready  for  its  instanta- 
neous cessation.  For  if  the  power  which  expands  the  glass 
at  first  be  continued  in  full  force,  the  glass  will  suddenly 
burst  out  into  a  large  irregular  thin  bubble  of  no  use.  This 
follows  as  a  natural  consequence,  for  every  enlargement  of 
the  bubble  diminishes  its  thickness,  and  consequently  its 
resistance,  and  at  the  same  time  increases  its  internal  area, 
and  in  that  respect  increases  the  power  of  the  air  impelled 
into  it;  and  if  the  enlargement  take  place  quickly,  so  that 
the  glass  has  not  time  to  cool,  it  cannot  but  happen  that  the 
bubble  should  expand  to  a  large  size.  To  avoid  this,  air 
should  be  thrown  in  from  the  mouth  only  (223),  and  not 
from  the  lungs:  as  the  glass  expands,  the  force  with  which 
the  air  is  impelled  should  be  diminished;  and  the  operator 
should  not  endeavour  to  finish  the  bulb  at  once,  but  having 
succeeded  in  expanding  it  to  such  a  size  that  the  internal 
diameter  is  five  or  six  times  the  thickness  of  the  glass,  he 
should  heat  it  again,  and  complete  the  bulb  at  a  second 
operation. 

1195.  The  glass  must  never  be  blown  whilst  it  is  in  the 
flame,  it  being  impossible  to  make  it  retain  an  uniform  tem- 
perature there,  but  is  always  to  be  expanded  in  the  air:  as  it 
swells  it  must  be  continually  turned,  and  those  parts  which 
are  thinnest  brought  to  the  lowest  position;  they  are  easily 


GLASS  TUBES  EXPANDED.  537 

recognised  by  their  sudden  expansion,  by  a  greater  degree 
of  transparency,  and  a  peculiar  reflection  from  them  different 
from  that  of  the  neighbouring  parts.  They  are  directed  to 
be  brought  into  the  lowest  situation,  because  the  glass  in 
that  position  cools  most  rapidly,  and  consequently  its  further 
extension  is  prevented.  The  operation  must  be  quick  to  be 
good,  for  the  temperature  of  the  thin  glass  is  so  soon  low- 
ered, that  it  cannot  be  done  at  all  if  not  rapidly.  The  bulb 
when  finished  should  be  round,  set  straight  on  the  end  of 
the  tube,  of  uniform  thickness  at  the  bottom  and  sides,  and 
without  lumps  or  knots.  The  size  will  vary  with  its  thick- 
ness and  the  quantity  of  glass  heated. 

1 196.  These  operations  may  then  be  repeated  with  tubes  of 
different  sizes.     If  their  internal  diameters  are  much  smaller 
than  that  mentioned,  as  in  thermometer  tubes,  the  end  may 
be  heated  until  almost  solid,  and  even  thrust  up  into  a  lump. 
This  being  uniformly  ignited,  should  be  blown  until  the  air 
just  begins  to  expand  in  a  small  bubble  at  the  end  of  the 
bore,  and  then  the  temperature  of  the  glass  being  well  raised, 
it  should  be  blown  out  into  a  bulb  at  once,  being  turned  in 
the  air  as  before  directed  during  the  operation.     It  will  be 
understood  from  what  has  been  said  (277,  1252),  that  these 
bulbs  will  not  serve  for  thermometers,  because  of  the  mois- 
ture they  receive  from  the  air  thrown  in  by  the  lungs;  but 
they  are  useful  in  the  practice  they  afford,  and  for  numerous 
experimental  purposes*. 

1197.  Sometimes  an  expansion  is  required  in  the  middle 
of  a  tube  (558,  957),  and  the  operation  in  general  resembles 
that  just  described.     If  the  end  of  the  tube  be  closed,  the 
glass  merely  requires  to  be  thickened  and  heated  at  the  part 
to  be  blown  out,  and  then  expanded  by  the  breath.     If  it  be 
not  closed  at  either  extremity,  then  the  finger  or  a  cork  must 
be  applied  to  one  end  to  close  it,  and  the  proper  part  being 
heated,  the  lips  are  to  be  applied  to  the  other  end,  and  the 
expansion  made. 

*  Instead  of  the  mouth,  thermometer  makers  blow  the  bulbs  by  means  of  a 
gum  elastic  bag,  into  the  neck  of  which  is  fitted  a  perforated  cork.  Care  must 
be  taken  to  thrust  the  stem  into  the  aperture  in  the  cork  after  the  tube  is  heated, 
and  to  keep  the  bag  compressed  after  the  inflation  of  the  bulb,  until  it  hard- 
ens.— Ei>. 

3S 


538  TUBES  CONVERTED  INTO  VESSELS. 

1198.  A  little  practice  of  this  kind  wiil  soon  enable  the 
student  to  remove  the  knots  at  the  end  of  his  closed  tubes 
(1168),  and  make  their  terminations  perfectly  round,  and 
uniform  in  thickness.     By  similar  trials  he- will  succeed  per- 
fectly in  forming  the  little  vessels  formerly  referred  to  (97), 
some  of  which  are  blown  out  of  small   tubes,  whilst  others 
may  often   be  made  without  any  blowing  at  all.     For  this 
purpose  it  is  only  necessary  to  take  a  piece  of  tube  of  the 
proper  diameter,  or  if  too  large  at  first  it  must  be  drawn 
down  to  the  diameter  required  (1166),  and  contracting  one 

part  into  a  neck  of  such  width  as  is  necessary  to  be 
given  to  the  intended  vessel  (1167),  the  flame  is  after- 
wards to  be  removed  further  down,  to  fuse  the  glass, 
which  is  to  be  contracted,  drawn  out,  and  closed.  In 
this  way  the  body  of  the  vessel  is  obtained  of  any  re- 
quired capacity,  according  to  the  length  given  to  the 
piece  of  tube  forming  it;  or  by  warming  the  body  and 
then  blowing  it,  it  may  be  expanded  until  of  much 
larger  size.  The  flask  is  afterwards  to  be  separated  from 
the  remaining  piece  of  tube,  either  by  cutting  it  with  a  file 
(1152),  or  drawing  it  off*  at  the  lamp  to  a  fine  termination, 
if  required. 

1199.  The  bulbs  referred  to  (76,  110)  are  made  in  a 
similar  way.     A   piece  of  small  tube  is  to  be  drawn  out, 
closed,  and  the  end  rounded.     The  end  of  the  piece  of  tube 
drawn  off  is  to  be  melted  in  the  lamp,  and  suddenly  applied 
to  the  extremity  of  the  tube  just  closed,  which,  if  at  a  tem- 
perature below  the  soft  point  of  the  glass,  will  allow  of  its 
adhesion  in  a  manner  sufficiently  strong  to  bear  the  force  re- 
quired in  working  and  finishing  the  vessel,  yet  so  slight,  that 
a  feeble  tap  or  blow  will  readily  cause  its  separation.     So 
arranged,  the  glass  tube  is  to  be  heated  a  little  way  from4he 
end,  that  a  sufficient  length  of  it  to  form  the  bulb  may  be 
drawn   away  by  the  attached  fragment,  and  finally  hermeti- 
cally sealed  in  the  manner  already  described  (1 190).     When 
cold  it  is  to  be  tapped  against  the  table ;  it  will  then  separate 
from  the  waste  piece  of  glass  which  previously  supported  it, 
and  will  be  ready  for  use. 

1200.  Two  pieces  of  tube  are  sometimes  to  be  melted  to- 


TUBES  JOINED WIRES  INSERTED.  539 

gether  so  as  to  form  one,  with  a  continuous  bore ;  and  pieces 
of  the  same,  or  of  very  different  thickness,  may,  if  necessary, 
be  joined.  The  ends  should  be  straight,  and  of  nearly  equal 
diameter,  so  as  to  apply  almost  accurately  against  each  other. 
If  they  are  not  so  at  first,  the  extremity  of  the  larger  one 
should  be  contracted  until  they  become  so.  They  should  be 
brought  into  the  flame  so  as  to  be  raised  separately,  but  at 
the  same  time  to  a  good  heat,  that  the  glass  may  be  quite 
soft;  and  then  the  ends,  being  applied  to  each  other,  should 
be  pressed  together  in  the  flame,  until  the  glass  adheres  in 
every  part,  and  runs  up  into  a  ring  round  the  tube.  The 
ring  should  be  immediately  drawn  down  again,  unless  it  be 
permanently  required,  and  then  by  working  the  glass  in  the 
flame,  the  joint  should  be  brought  into  a  good  shape  and  con- 
dition. If,  during  the  operation,  the  tube  contracts,  it  should 
be  blown  out  (1197);  if  it  become  thin,  it  must  be  thickened 
(1172)  and  pushed  up;  if  it  be  thickened  too  much,  it  must 
be  pulled  out  and  rendered  thinner,  the  contraction  of  the 
diameter  occasioned  by  doing  so  being  rectified  by  expand- 
ing the  glass  again  (1 197).  The  joint,  when  finished,  should 
not  be  of  imperfect  adhesion  at  any  part,  or  distorted  in 
form,  or  involve  any  great  irregularity  of  thickness,  for  then 
it  will  almost  certainly  fly  asunder  when  cold.  Small  irre- 
gularities may  be  allowed  to  remain,  and  if  the  glass  be  well 
annealed,  will  do  no  harm. 

1201.  It  is  of  great  importance  in  many  experiments  to  be 
able  to  seal  a  metallic  wire  into  glass,  so  that  the  latter  shall 
close  round  it  and  adhere  to  it,  in  a  manner  perfectly  air-tight 
and  sound.  The  detonating  eudiometer  tubes  (994),  and  the 
tubes  for  the  collection  of  gas  (1046,  1049),  during  the  vol- 
taic decomposition  of  liquid  substances  in  solution,  are  com- 
mon instances  of  their  valuable  application.  Platinum  is  the 
only  metal  which  answers  well  for  this  purpose,  and  fortu- 
nately it  is  that  which,  in  consequence  of  its  chemical  rela- 
tions, is  the  most  useful  in  such  situations.  The  superiority 
of  platinum  depends  upon  its  in  fusibility  at  the  temperatures 
required  to  work  the  glass,  and  on  the  close  agreement  of 
glass  and  platinum,  in  the  rate  of  their  expansion  and  con- 
traction by  changes  of  temperature.  Other  metals,  as  iron, 


540  WIRES  SEALED  INTO  TUBES. 

differ  much  from  glass,  and  when  wires  of  these  are  inclosed 
in  the  most  secure  manner,  they  either  separate  when  cold 
from  the  glass,  by  contraction,  destroying  the  continuity  all 
round  them,  or,  if  that  does  not  take  place,  they  retain  the 
glass  in  the  immediate  neighbourhood  in  such  a  state  of  ten- 
sion, that  very  slight  accidents  cause  it  to  fly,  and  cracks  to 
proceed  from  the  wire  into  the  glass  in  several  directions. 
This  rarely  happens  with  platinum  inclosed  in  the  thickest 
glass,  if  the  junction  has  been  good,  and  the  glass  well 
softened. 

1202.  Suppose  a  tube  like  that  figured  (1050),  be  required, 
with  a  platinum  wire  passing  through  it,  and  hermetically 
sealed  into  its  summit.  A  piece  of  tube  of  the  required  di- 
ameter, thickness,  &c.,  is  to  be  selected,  and  also  a  piece  of 
clean  wire:  the  tube  should  be  heated  at  the  part  where  it 
is  to  be  closed,  and  should  be  drawn  out  so  as  to  form  a  ca- 
pillary neck  (1172,  1184),  the  end  of  the  tube  and  the  neck 
being  preserved  of  considerable  comparative  thickness,  so 
that  no  occasion  for  afterwards  increasing  it  shall  exist.  The 
neck  should  be  of  such  internal  diameter  as  freely  to  receive 
the  wire,  but  no  more,  and,  when  cold,  should  be  cut  with  a 
2,  file,  so  as  to  leave  the  proportion 

^l/a'          represented  in  the  figure  attached 

O1  J^  to  the  tube.     The  wire  is  to  be 

introduced  through  the  aperture 

thus  opened,  and  placed  in  the  position  required  when  the  tube 
shall  be  completed.  The  point  of  the  flame  is  then  to  be  ap- 
plied first  to  a,  that  the  extremity  of  the  aperture  may  be- 
come heated  and  the  wire  also,  the  temperature  being  kept 
down  to  such  a  point  as  is  sufficient  to  soften  the  glass  con- 
siderably, but  not  to  make  it  run ;  and  both  glass  and  wire 
being  hot,  a  very  little  motion  of  the  latter  will  cause  the 
edge  of  the  former  to  adhere  to  it  all  round,  and  make  a  tight 
though  not  a  strong  joint.  This  done,  the  heat  must  be  ap- 
plied more  towards  the  tube,  so  as  to  make  the  glass  and  the 
wire  adhere  gradually  from  a  to  b.  This  should  be  done 
without  «any  twisting  or  distortion  of  the  glass,  and  will  be 
found  more  or  less  easy,  according  as  the  end  of  the  tube  has 
been  well  or  ill  prepared  at  first  to  receive  the  wire.  Finally, 


TWO  WIRES  INSERTED.  541 

all  that  part  by  which  the  wire  is  surrounded  and  held, 
should  be  raised  to  such  a  temperature  as  to  make  the  glass 
soft  and  semi-fluid,  that  no  irregularities  in  form  or  contrac- 
tion may  remain;  the  wire  should  be  arranged  so  that  it 
passes  directly  down  the  axis  of  the  tube,  and  then  the  whole 
must  be  suffered  to  cool.  It  is  erroneous  in  a  beginner  to 
make  the  capillary  end  of  his  tube  thin,  and  trust  to  thicken- 
ing it  after  the  wire  is  sealed  in  by  running  the  glass  up. 
Such  sealings  are  generally  unsafe.  The  end  of  the  tube 
should  first  be  made  of^sufficient  thickness,  and  then  all  that 
remains  to  be  done  is,  to  soften  it,  so  that  it  may  collapse 
round  and  adhere  perfectly  to  the  hot  wire,  in  every  part  of 
the  joint. 

1203.  When  a  tube  of  this  kind  is  required  for  voltaic  de- 
compositions, having  two  parallel  but  insulated  wires  sealed 
into  its  closed  extremity  (1049),  then  a  piece  of  platinum 
wire  of  sufficient  length  for  the  two  is  to  be  bent  in  the  mid- 
dle, so  that  the  two  parts  may  be  parallel  at  the  distance  of 
the  eighth  or  twelfth  of  an  inch  from  each  other.  The  ex- 
tremities are  to  be  fixed  into  a  small  piece  of  cork,  which  will 
retain  the  bent  wire  so  steadily,  that  it  may  be  worked  with 
as  a  single  piece.  That  part  of  the  wire  which  is  intended 
to  pass  through  the  end  of  the  tube,  and  to  be  fixed  in  the 
glass,  is  to  be  brought  into  the  flame  of  the  lamp,  and  a  thick 
filament  of. glass,  or  a  thin  rod  being  held  in  the  hand,  its 
extremity  is  to  be  softened  also  in  the  flame,  and  glass  from 
it  worked  upon  the  wires,  so  as  to  form  a  small  bead,  which, 
lying  between  them,  shall  also  extend  outside  of,  and  inclose 
them  on  two  of  its  sides,  and  when  cold  serve  to  tie  them  to- 
gether at  the  distance  before  arranged.  This  done,  the  end 
of  the  tube  is  to  be  prepared,  by  drawing  it  down  and  con- 
tracting it,  but  only  so  much,  that  when  the  neck  is  cut  off 
(which  should  be  done  closer  to  the  tube  than  in  the  former 
case — 1202),  the  aperture  may  be  so  large  as  to  admit  the 
passage  of  the  double  wire,  but  not  of  the  bead  of  glass  upon 
it.  The  wire  is  to  be  dropped  down  the  inside  of  the  tube, 
so  that  its  bent  end  may  pass  through  the  aperture,  and  the 
glass  bead  be  received  and  stopped  just  within  it;  heat  is  now 
to  be  applied  to  melt  the  bead  and  the  end  of  the  glass  tube 


542  WIRES  FIXED  IN  TUBES AT  THE  SIDES. 

together,  and  the  temperature  is  to  be  raised  until  the  cohe- 
sion is  perfect,  and  the  joint  well  formed,  after  which  it  must 
be  allowed  to  fall.  When  the  tube  is  cold,  the  piece  of  cork, 
now  within,  is  to  be  drawn  from  the  ends  of  the  wire,  and  the 
wire  itself  is  to  be  divided  on  the  exterior,  at  the  bend.  It 
thus  forms  two  insulated  portions,  which  may  be  connected 
with  the  poles  of  a  battery,  and  rendered  active  in  decom- 
posing any  solution  put  into  the  tube. 

1204.  If  a  wire  is  to  be  inserted  through  and  sealed  into 
the  side  of  a  tube,  that  part  of  the  |ube  through  which  the 
wire  is  to  pass  is  to  be  softened  in  the  lamp,  and  the  wire 
pressed  against  it  until  it  appears  in  the  interior  of  the  tube; 
it  should  then  be  drawn  out  again  in  the  same  direction,  and 
both  tube  and  wire  left  to  cool.  The  wire'-will  be  found 
coated  with  glass,  which  may  easily  be  broken  off.  The 
tube  will  be  drawn  out  at  the  place  forming  a  conical  pro- 
jection, the  end  of  which,  when  broken  off,  will  afford  a 
passage  to  the  interior*.  The  wire  is  then  to  be  put  into 
the  aperture,  heated,  and  the  glass  fused  around  it:  ulti- 
mately the  wire  is  to  be  pushed  inwards,  until  that  portion 
of  glass  which  projected  has  been  returned  nearly  to  its  first 
position.  By  a  little  practice  this  may  be  done  so  that  the 
glass  shall  be  in  perfect  contact  with  the  wire  on  all  sides, 
and  with  little  disturbance  as  to  its  form  or  position  from 
that  which  it  possessed  at  first,  the  wire  a,t  the  same  time 
having  the  exact  position  required.  If  fears  be  entertained 
that,  from  the  removal  of  glass  on  the  wire,  and  by  breaking 
off  the  end  of  the  projection,  enough  will  not  remain  to  con- 
fer sufficient  strength  upon  the  tube  in  that  part,  it  will  be 
desirable  to  put  a  bead  of  glass  round  the  wire,  in  the  man- 
ner just  described  for  double  wires  (1203),  and  when  the 
heat  is  applied,  to  work  it  into  contact  with  the  glass  of  the 
tube,  that  the  latter  may  be  of  sufficient  strength.  When 
two  wires  are  required  in  the  same  tube,  at  a  certain  dis- 

*  I  find  the  following  method  easier.  Bend  a  strong  iron  wire  near  its  end  at 
right  angles,  and  sharpen  the  point;  heat  the  part  of  the  tube  into  which  the 
platinum  wire  is  to  be  fixed,  and  by  means  of  the  bent  iron  wire  passed  into  the 
open  end  of  the  tube,  push  laterally  outwards  so  as  to  form  a  small  glass  cone. 
A  file  easily  removes  its  apex,  and  leaves  an  aperture  for  the  insertion  of  the  pla- 
tinum.— ED. 


GLASS  TUBES  WORKED  BY  SPIRIT  LAMP.  543 

tance  from  each  other,  as  is  necessary  in  an  eudiometer,  the 
distance  is  easily  regulated  by  a  little  previous  considera- 
tion; allowance  being  made  for  the  extent  to  which  the 
wires  will  require  to  be  moved,  before  the  operation  is 
finished,  and  they  are  finally  fixed  in  their  places. 

1205.  After  some  pjpctice  in  softening  glass,  drawing  out 
and  sealing  tubes,  &c.,  it  will  be  found  easy  to  extend  the  art 
of  working  this  substance  by  forming  it  into  various  shapes. 
Thus  the  softened  end  of  a  tube  may  be  opened  out  by  the 
use  of  a  pair  of  cold  scissors  or  a  piece  of  clean  iron  (1147), 
attending  to  the   precautions  of  temperature  before  men- 
tioned  (1163),   and   thus  small  glass  funnels,  compressed 
tubes,  lipped  tubes,  &c.,  may  be  made  with  facility. 

1206.  When  green  bottle  glass  tube  is  to  be  worked  and 
submitted  to  these  operations,  they  will  be  found  more  diffi- 
cult of  performance,  because  of  the  much  higher  temperature 
required  for  the  fusion  of  this  glass.     Generally  it  is  only  the 
simpler  operations  that  are  necessary  with  green  glass,  such 
as  bending,  closing,  or  lengthening  a  tube.     These  may  be 
performed  readily  by  means  of  the  table  blow-pipe;  and  as, 
from  the  greater  strength  and  infusibilily  of  green  glass,  it 
frequently  happens  that  a  thinner  tube  of  this  substance  may 
be  used  than  of  flint  glass,  a  greater  facility  in  the  operation 
is  on  that  account  obtained. 

1207.  The  use  of  the  spirit-lamp  in  these  operations  on 
glass,  even  when  not  urged  by  a  blow-pipe,  has  been  noticed 
more  than  once.     When  its  powers  are  increased  by  the 
application  of  the  blow-pipe  (216,  &c.),  it  may  often  be 
made  to  perform  the  work  of  the  table-lamp;  generally  not 
so  well,  though  very  usefully;  sometimes  quite  as  well;  occa- 
sionally even  better.     Small  tubes  may   be  bent,  closed, 
drawn  out,  extended,  and  worked,  in  almost  any  way  by  its 
means ;  and  moderately  large  tubes,  i.  e.  from  one  third  to 
half  an  inch  in  diameter,  may  be  bent  and  closed  by  it.     If 
no  other  kind  of  blow-pipe  than  thjat  for  the  mouth  is  at 
hand,  it  must  be  turned  to  account  in  the  best  manner  poss- 
ible.    For  this  purpose  the  mouth-piece  of  the  blow-pipe 
may  be  placed  between  the  lips,  and  the  instrument  sup- 
ported without  any  help  from  the  hands,  being  allowed  to 


544 

hang  from  the  mouth  with  its  jet  opposite  to  the  flame  of 
the  spirit-lamp.  The  flame  may  then  be  urged,  whilst  both 
hands  remain  at  liberty  for  the  purpose  of  moulding  and 
working  the  glass.  The  student  will  at  first  find  it  difficult 
to  hold  the  blow-pipe  so  steadily  in  his  mouth  as  to  produce 
a  certain  and  regular  flame;  but  he  may  obtain  assistance  by 
placing  a  block  of  wood,  a  book,  a  weight,  or  a  brick  upon 
the  table,  between  himself  and  the  lamp,  at  such  a  distance 
from  the  latter  that  the  back  of  the  blow-pipe  may  bear 
slightly  against  it.  If  these  steadying-blocks  be  formed 
with  a  deep  wedge-shaped  notch  in  them,  or  if  a  block  of 
lead  be  purposely  prepared  with  such  a  notch,  then  this 
temporary  adjustment  is  much  more  securely  made;  but  if 
there  be  no  notch,  the  pressure  may  be  easily  regulated  by 
the  mouth,  and  will  be  quite  sufficient  to  render  the  blow- 
pipe, and  consequently  the  flame  itself,  perfectly  steady. 

1208.  Dr  Knight  informs  me  that  he  has 
long  used  a  very  convenient  mouth  blow- 
pipe stand  of  the  form  depicted,  the  spike 
at  the  bottom  enters  a  hole  in  a  board 
two  or  three  inches  high,  and  therefore 
allows  of  adjustment.  The  blow-pipe  is 
fixed  by  a  few  folds  of  soft  paper  in  the 
fork,  and  so  rendered  steady. 

1209.  The  cutting  of  glass  in  the  laboratory  is  an  opera- 
tion which  is  more  frequently  to  be  performed  with  the  tube 
and  rod  than  any  other  form  of  glass  (1152).     But  occa- 
sionally old  flasks,  retorts,  jars,  &c.,  are  required  to  be  cut 
into  useful  pieces,  and  several  methods  have  been  devised 
for  the  purpose.     These,  though  not  at  all  equal  in  accuracy 
and  security  to  the  methods  of  the  glass-worker,  may  be 
performed  with  such  common  tools  as  are  to  be  found  almost 
every  where,  require  but  little  practice,  are  frequently  effi- 
cient in  facilitating  experiments,  and  highly  useful   to  the 
student. 

1210.  The  method  of  cutting  tube  or  rod  by  a  file  has 
been  already  described  (1152).     A  cutting  diamond  will 
answer  the  purpose  as  well  as  a  file,  and  even  a  sharp  flint 
may  be  used  upon  emergency.     When  the  tube  is  very  large, 


CUTTING  OF  6LASS BY  RINGS.  545 

it  is  safer  to  go  round  the  place  first  with  a  diamond,  and  to 
perform  the  operation  over  a  cloth  or  some  other  soft  sub- 
stance, lest  as  the  pieces  separate  they  should  fall  and  be 
broken. 

1211.  In  all  cases  in  which  a  diamond  is  used,  it  must  be 
remembered  that  a  cut,  not  a  scratch,  is  required.     A  scratch 
by  a  diamond  will  rarely  give  direction  to  a  crack,  and  is  as 
likely  to  be  crossed  by  one  as  followed.     A  cut,  on  the  con- 
trary, is  a  division  of  the  glass,  independent  of  the  abrasion, 
has  actually  penetrated  to  some  depth*,  and  is  almost  cer- 
tain to  be  followed  by  any  crack  or  entire  division  that  may 
come  across  or  even  near  to  it.     A  cutting  diamond  operate 
well  only  in  one  particular  position;  which  should  be  found 
by  trial  upon  a  piece  of  crown  glass,  and  being  ascertained 
should  be  marked  upon  the  handle,  that  in  any  future  op 
ration  it  may  always  be  in  the  same  favourable  position  re- 
lative to  the  cut  that  is  to  be  made.     The  scratching  diamond 
(128,  974)  is  not  fit  for  cutting,  but  is  intended  for  distinct 
uses;  nor  should  a  cutting  diamond  be  injured  by  employing 
it  in  writing  and  scratching  upon  glass. 

1212.  Old  retorts,  flasks,  globes,  and  other  convex  pieces 
of  glass  apparatus,  are  often  cut  by  iron  rings  into  circular 
pieces,  which  then  answer  the  purpose  of  dishes.     The  rings 
should  be  of  different  diameters,  made  of  wrought  iron  about 
the  third  of  an  inch  in  thickness,  with  a  stem  attached  to 
them,  by  which  they  are  fixed  into  a  wooden  handle.     When 
made  uniformly  red  hot,  and  brought  into  close  contact  with 
the  convex  surface  of  a  glass  retort  or  flask,  a  crack  gene- 
rally takes  place  in  a  few  moments  beneath  the  ring,  which 
occasions  the  separation  of  the  inner  round  piece.     These 
pieces  are  sometimes  used  as  evaporating  basins;  but  from 
their  great  tendency  to  crack  at  the  edges  and  gradually 
break  to  pieces,  are  not  safe  in  precise  or  important  experi- 
ments.    The  uses  of  the  rings  are  much  more  valuable  for 
the  facility  with  which  they  cut  a  flask  in  half,  or,  by  simi- 
lar operations,  afford  entrance  into  any  other  vessel  so  as  to 


*  See  Wollaston,  Phil.  Trans.  1816,  p.  265, 

3T 


546  CUTTING  GLASS — BY  MOT  1II<5N — STRING. 

allow  of  an  examination  of  the  interior,  and  the  state  of  the 
substances  it  contains*. 

1213.  Thin  fragments  of  retorts,  flasks,  and  especially 
Florence  flasks,  are  very  useful  for  the  evaporation  of  small 
quantities,  but  as  these  vessels  are  never  required  to  be  thus 
cut  up  until  they  are  broken, -the  cracks  then  existing  may 
be  led  in  advantageous  directions  more  conveniently  by  other 
means  than  by  the  iron  rings. 

1214.  Many  pieces  of  glass  apparatus  which  have  become 
useless,  such  as  bottles,  jars,  globes,  and  generally  those 
with  convex  surfaces,  may  be  divided  along  a  particular  line 
by  means  of  a  hot  iron  rod,  and  thus  separated  into  useful 
pieces.     The  operation  consists  in  leading  a  crack,  either 
made  for  the  purpose  or  previously  existing,  according  to  the 
required  direction.     The  iron  rod  may  be  nearly  as  thick  as 
<the  little  ringer,  and  made  tapering  at  the  end  for  an  inch  or 
an  inch  and  a  half  to  a  blunt  point.     The  line  of  division 
should  be  decided  upon,  and  even  be  marked  on  the  glass  with 
pen  and  ipk;  it  maj  pass  without  impropriety  over   parts 
varying  in  thickness,  but**  should  not  go  suddenly  from  a 
thick  to  a  thin  part:  thus  it  may  be  followed  with  ease  round 
the  sides  of  ^  jar  or  bottlje,  but  the  crack  could  scarcely  be 
led  down  one  "side  of  a  jar,  across  the  bottom,  and  up  the 
other  side.      ^ 

1215.  It  will  rarely  occur  that  a  vessel  is  to  be  divided,  in 
which  some  previous  crack  or  broken  edge  does  not  exist. 
The  iron,  being  heated  to  dull  redness,  is  to  be  brought  with 
its  point  towards  the  crack  in  an  opposite  direction  to  it,  and 
the  apex  is  to1  be  laid  upon  the  sound  glass  just  before  the 
crack,  the  iron  rod  being  at  the  same   time  retained  at  an 
angle  of  about  twenty  or  thirty  degrees,  with  the  as  yet  un- 


*  The  old  mode  of  dividing  glass  tubes,  when  large  and  thick,  is  not  noticed 
by  our  author.  It  consists  in  heating  a  narrow  ring  of  the  tube  by  the  friction  of 
a  coed  passed  once  round  it,  and  kept  in  rapid  motion  to  and  fro.  The  sudden 
application  of  cold  water  to  the  heated  ring  of  glass,  causes  the  division  of  the 
tube.  The  greatest  difficulty  in  conducting  this  process  is  found  in  keeping  the 
string  in  one  place.  Dr  Hare  overcomes  that  impediment  by  placing  the  tube  in 
an  angular  notch  made  in  the  end  of  a  piece  of  board,  and  the  string  in,  a  slit  at 
light  angles  to  the  direction  of  the  tube.  By  this  arrangement,  tubes  of  very 
forge  size,  large  phials,  and  with  care,  even  bottles  may  be  neatly  divided. — ED. 


LEADING   A  CRACK.  547 

cracked  glass  beneath.  The  crack  will  immediately  extend 
itself  to  the  part  of  the  glass  with  which  the  hot  iron  is  in  con- 
tact; and  by  gradually  and  slowly  drawing,  the  latter  along 
the  glass  before  the  crack,  the  division  will  follow  it,  and 
may  thus  be  led  in  almost  any  direction.  It  may,  when  not 
carried  too  near  to  the  edge  or  to  another  crack,  be  made  to 
turn  off  suddenly  at  right  angles  to  its  former  course,  or  it 
may  be  led  in  gradually  winding  and  curved  lines.  The 
crack  should  at  first  be  led  directly  towards  the  line  which 
marks  the  convenient  division,  and  having  reached  it,  that 
line  is  to  be  pursued  until  the  separation  is  effected.  When 
the  rod  has  cooled  considerably,  or  even  when  hot,  if  thin 
glass  be  experimented  with,  it  is  often  difficult  to  carry  the 
crack  entirely  round  into  the  commencement  or  into  any 
other  division ;  but  in  such  cases  the  small  part  which  remains 
undivided  easily  yields  to  the  slightest  mechanical  force,  the 
crack  being  then  continued  directly  into  the  previously  di- 
vided part. 

1216.  The  rapidity  with  which  a  division  is  effected  de- 
pends upon  the  temperature  of  the  rod.     It  is  not  desirable 
to  perform  it  very  quickly,  and  therefore,  when  very  hot,  the 
rod  should  be  held  at  greater  angles  with  the  glass  than 
those  mentioned,  that  the  point  only  may  touch  it.     As  the 
heat  diminishes  the  rod  should  be  more  inclined,  that  the 
thicker  part  may  be  made  to  approach  the<glass,  and  by  its 
heat  and  effect  compensate  for  the  diminished  temperature  of 
the  point.     When  still  cooler,  it  may  be  desirable  to  use  the 
thickest  part  of, the  rod  instead  of  the  point,  laying  it  down 
in  contact  with  the  glass  before  the  crack  and  drawing  it 
along,  but  this  can  only  be  done  on  convex  vessels. 

1217.  If  the  direction  to  be  followed  lies  but  a  little  dis- 
tance from  the  line  of  an  edge,  or  a  previous  division,  the 
operation  must  be  performed  more  slowly,  and  with  the  apex 
rather  than  the  line  of  the  rod;  for  the  crack  to  be  led  has 
then  a  tendency  to  fly  suddenly  to  the  edge  by  its  side.     It 
is  not  easy  by  this  method  to  cut  nearer  to  an  edge  than  the 
third  or  fourth  of  an  inch. 

1218.  If  there  be  no  crack  to  commence  with,  one  must 
be  produced  in  the  following  mariner.     If  possible  an  edge 


548  LEADING  A  CRACK MAKING  ONE. 

is  to  be  selected,  which,  being  an  inch  or  an  inch  and  a  half 
from  the  line  of  division,  may  have  a  crack  made  in  it  with- 
out interfering  with  the  part  of  the  glass  intended  to  be  pre- 
served ;  if  it  be  a  recent 'edge,  i.  e.  one  that  has  been  formed 
by  fracture,  rather  than  one  which,  existing  at  first  on  the 
piece  of  apparatus,  has  i  een  fused,  it  is  the  more  advantage- 
ous. The  heated  iron  rod  is  to  be  applied  to  this  edge  in  a 
direction  almost  perpendicular  to  the  glass,  that  the  heat  may 
extend  to  as  little  distance  from  the  place  as  possible,  and 
when  it  has  been  in  contact  for  a  moment,  if  a  division  has 
not  spontaneously  occurred,  the  hot  part  is  to  be  touched  with 
a  moistened  finger :  a  crack  will  immediately  be  occasioned} 
and  the  smaller  the  distance  to  which  it  runs  from  the  edge 
the  better;  for  once  commenced,  the  smallest  crack  can  be 
led  as  easily  as  the  largest,  and  the  opportunity  of  directing 
it  from  the  commencement  is  secured.  If  the  glass  be  thick, 
as  that  of  a  bottle  or  jar,  it  will  usually  fly  by  the  heat  alone; 
if  it  be  thin,  as  that  of  a  Florence  flask,  it  will  generally  re- 
quire the  application  of  moisture  after  the  heat. 

1219.  If  the  crack  is  to  be  commenced  in  the  middle  of  a 
plane  unbroken  surface,  great  care  is  required,  or  the  frac- 
ture will  extend  to  a  considerable  distance,  and  probably  in 
a  wrong  direction.     The  heated  point  should  be  applied  to  a 
single  spot,  and  being  soon  removed,  the  place  should  be 
moistened.     It  is  better  to  try  two  or  three  times  unavail- 
ingly,  than,  by  heating  the  glass  too  much  at  first,  to  incur 
the  risk  of  an  extensive  fracture.     The  crack  should  always 
be  commenced  at  some  distance  from  the  important  line  of 
division,  that  there  may  be  less  danger  of  the  first  and  uncer- 
tain separation  interfering  with  or  crossing  the  latter. 

1220.  In  all  divisions  of  this  kind  the  glass  to  be  cut  should 
be  supported  upon   a  cloth,  that  the  parts  on  both  sides  of 
the  crack  may  be  sustained;  or,  when  the  division  approaches 
its  completion,  the  mere  weight  of  one  part  may  make  the 
crack  run  in  an  inconvenient  direction.     The  form  of  the 
piece  of  iron  is  by  no  means  essential,  and  a  furnace  poker, 
or  a  pair  of  tongs  may,  in  cases  of  emergency,  be  used  for 
these  purposes.     It  may  even  be  performed  with  a  red  hot 


OLD  GLASS  MADE  USEFUL.  549 

pointed  piece  of  charcoal,  the  ignition  being  heightened  by 
blowing  upon  it. 

1221.  The  edges  which  are  exposed  when  glass  is  thus 
divided  are  very  liable  to  fracture  by  slight  mechanical  force, 
heat,  or  other  causes,  much  more  so   indeed  than  glass  of 
which  the  edges  have  been  fused  or  ground.     Hence  it  is 
frequently  advantageous  either  to  grind  them,  which  may  be 
done  upon  a  flat  stone  with  a  little  sharp  sand  or  emery  and 
water  (1229);  or  to  soften  and  fuse  them,  which  may  be  ef- 
fected either  by  the  table  blow-pipe,  bringing  all  parts  of 
the  edge  in  succession  into  the  flame,  or  by  a  shallow  char- 
coal fire.     When  the  edges  are  not  thus  finished,  they  should 
have  a  sand-stone  or  a  fine  file  passed  over  them  to  remove 
the  linear  angles,  which,  being  sharp,  are  dangerous  to  the 
fingers. 

1222.  Jars  which  have  been  broken  at  the  edges  may,  by 
a  process  of  this  kind  be  cut  down,  and  then  will  long  re- 
main useful  vessels.     Bottles  of  which  the  necks  or  upper 
parts  have  been  broken  may  be  converted  into  small  jars. 
Their  stoppers  should  be  added  to  those  which  already  oc- 
cupy a  drawer  in  the  laboratory  (25,  1230),  and  from  which 
the  place  of  an  absent  one  may  often  be  supplied.     Broken 
test  glasses  may  frequently  be  cut  into  useful  forms;  if  but 
one-half  or  two-thirds  of  the  cup  be  removed,  the  remaining 
part  with  the  foot  will  serve  for  many  voltaic  decompositions, 
and  frequently  as  a  convenient  insulating  stand  in  electrical 
experiments.     If  nothing  but  the  foot  can  be  preserved,  still 
there  are  numerous  occasions  for  its  services  in  the  labora- 
tory; for  the  body  being  broken  away,  and  the  stem  chipped 
off,  which  is  done  by  striking  it  sideways  with  a  file  or  the 
edge  of  an  iron  spatula,  a  strong  round,  glass  disc  remains. 
Such  discs  are  very  convenient  as  covers  for  the  mouths  of 
glasses  containing  precipitates  or  other  substances,  to  ex- 
clude dust  during  the  time  the  experiments  are  in  progress 
(553). 

1223.  In  cutting  up  large  pieces  of  glass  by  the  method 
described,  especially  if  any  importance  be  attached  to  the 
result,  it  is  best  to  precede  the  application  of  the  hot  iron  by 
going  round  the  part  with  a  diamond.     The  iron  then  merely 


550  FLAT  GLASS  DIVIDED BY  A  FILE. 

completes  what  the  diamond  had  begun,  and  it  is  seldom 
that  the  separation  departs  from  the  track  thus  laid  down  for 
it.  But  the  chemist  should  never  undertake  delicate  or 
difficult  divisions;  the  object  of  the  preceding  directions  is 
to  enable  the  economical  experimenter  to  cut  up  into  useful 
forms  old  glass,  which  would  otherwise  be  thrown  away  as 
waste.  In  more  important  cases  he  will,  of  course,  transfer 
it  to  the  hands  of  an  instrument-maker. 

1224.  Sometimes  it  is  required  that  a  piece  of  flat  glass, 
as  crown  glass,  should  be  broken  into  two  or  three  smaller 
pieces.  If  this  be  attempted  by  means  of  a  blow,  the  glass 
will  usually  shiver  into  many  pieces,  mostly  long,  with  curved 
outlines,  and  of  very  inconvenient  forms;  a  piece  of  the  de- 
sired size  or  shape  being  rarely  obtained.  But  by  contrivance 
a  piece  of  such  glass  may  be  divided  into  two  parts  only, 
with  considerable  certainty,  the  direction  of  the  fracture  also 
being  in  some  degree  under  government;  and  a  long  slip  of 
glass  may  be%  divided  into  halves  or  quarters,  or  a  piece  of 
any  form  cut  up  into  smaller  parts  without  difficulty.  Sup- 
pose it  were  required  to  divide  a  piece  of  glass  four  inches 
long  and  two  wide,  into  two  nearly  equal  portions.  An  an- 
gular file  (three-square  or  four-square)  is  to  be  placed  with 
one  end  against  an  obstacle,  as  the  edge  of  a  table,  and  the 
other  against. the  breast,  so  that  by  a  little  pressure  it  may 
be  supported  with  one  of  its  edges  upwards,  and  nearly  in  a 
horizontal  line.  The  piece  of  glass  is  to  be  held  with  one 
end  in  each  hand,  and  the  middle  of  one  of  its  long  sides  is 
to  be  applied  to  the  edge  of  the  file  at  that  end  nearest  to  the 
table  or  support,  the  glass  being  inclined  a  little  upwards 
from  the  horizontal  direction  towards  the  operator.  The 
operator  is  then  to  press  with  a  moderate  degree  of  force  on 
the  glass,  drawing  it  along  the  file  from  one  end  to  the  other, 
and,  without  taking  it  off,  to  turn  it,  as  it  were  over,  so  as  to 
incline  it  in  the  opposite  direction,  and  immediately  carry 
the  glass  back  again  with  about  the  same  pressure,  to  its  ori- 
ginal place  on  the  edge.  In  this  way  there  is  a  tendency  to 
notch  the  glass  on  the  opposite  sides  of  the  same  edge  and 
place,  which  is  sufficient  to  originate  a  fracture  there;  and 
as  the  glass  is  returned,  it  generally  divides  in  the  hands  by 


GLASS  DIVIDED BY  PRESSURE.  551 

a  crack,  commencing  at  the  place  where  it  was  in  contact 
with  the  edge  of  the  file,  and  proceeding  directly  across  be- 
tween the  hands. 

1225.  The  degree  of  pressure  required  is  quickly  learnt  by 
a  little  practice  on  waste  pieces  of  crown  glass :  it  should  be 
insufficient  of  itself  to  break  the  glass,  but  sufficient  when 
the  small  fracture  is  commenced  by  the  file.     It  is  better  to 
make  it  rather  stronger  when   the  glass  is  returned,  than 
when  drawn  towards  the  body;  the  former  being  the  most 
convenient  time  and  position  for  the  fracture  to  take  place 
in.     The  direction  of  the  crack  is  regulated  chiefly  by  the 
force  applied  by  the  hands,  being  usually  across  the  line  of 
resistance  to  that  force;  and  hence  the  opportunity  afforded 
of  giving  it  a  direction  by  pressing  with  the  hands  equally 
on  each  side  of  the  line,  along  which  it  is  desired  the  crack 
should  pass,  at  the  same  time  making  it  commence  at  the 
beginning  of  that  line,  by  placing  it  on  the  edge  of  the  file. 

1226.  When  all  other  means  of  directing  a  crack  are  ab- 
sent, it  may  frequently  be  done  with  advantage  merely  by 
the  pressure  of  the  nail.     If  a  Florence  flask  be  cracked, 
the  division  may  be  extended  by  putting  the  thumb  over  it 
near  the  end  of  the  crack,  pressing  the  nail  when  in  contact 
with  the  glass,  and  carrying  the  thumb  forward.     The  crack 
will  fly  befpre  it,  extending  on  this  or  that  side,  according 
to  the  direction  in  which  the  thumb  advances,  or  according 
as  the  pressure  is  on  one  side  or  the  other.     The  flask  may 
thus  be  divided  into  pieces,  much  more  useful  than  such  as 
would  probably  result  from  crushing  or  breaking  it  entirely 
at  random. 

1227.  Pieces  of  glass  are  reduced  at  the  edges  in  various 
ways.     The  corners   may  be  removed  from  fragments  of 
plate-glass  by  running  a  coarse  file  with  a  light  and  rasping 
kind  of  motion  against  the  edges,  in  a  position  slightly  in- 
clined to  the  glass.     The  reduction  takes  place,  not  by  mere 
attrition  and  wearing  away,  but  by  the  removal  of  successive 
chips  of  glass,  each  tooth  of  the  file  carrying  away  a  small 
fragment,  perhaps  the  eighth  or  tenth  of  an  inch  across;  in 
fact  of  a  diameter  equal  to  the  whole  thickness  of  the  plate. 
In  this  way  the  large  pieces  are  soon  brought  into  a  round 


552  EDGES  REMOVED— GRINDING  OF  GLASS. 

form,  and  serve  as  plates  (1348).  In  the  same  manner  if, 
in  cutting  a  thick  tube,  the  aperture  should  not  be  level  all 
round,  the  projecting  parts  may  be  removed  piecemeal,  but 
more  care  is  required  than  with  flat  glass,  from  the  tendency 
of  cracks  to  form  at  the  edge  and  fly  up  the  tube*. 

1228.  The  edges  of  plate-glass  may  also  be  removed  by  a 
pair  of  pliers,  not  by  pinching  off  the  superabundance,  but 
by  bringing  it  between  the  chops  of  the  instrument,  holding 
it  lightly  there,  and  then  twisting  the  pliers  slightly  so  as  to 
exert  a  degree  of  pressure  upon  the  exterior  edge  of  the 
glass  by  one  of  the  sides,  whilst  the  other  merely  serves  as 
a  fulcrum  for  support  to  the  power.     The  edge  will  be  found 
to  splinter  and  crumble  away  under  a  force  thus  applied, 
and  the  art  of  successfully  using  it  is  soon  learned  by  prac- 
tice.    This  method  is  not  so  applicable  to  the  edges  of  tubes 
as  to  straight  glass,  but  it  may  often  be  used  with  crown 
glass  when  the  file  is  inapplicable. 

1229.  Glass  may  be  ground  on  almost  any  flat  stone  with 
a  coarse  grain,  by  means  of  a  little  sharp  sand  and  water,  or 
better  still,  by  emery  and  water.     Thus  the  ends  of  the  tubes 
(743,  1221)  may  be  ground  level  on  a  piece  of  Yorkshire  or 
Purbeck  stone.     The  operation  is  easy  in  -  proportion  to  the 
smallness  and  thickness  of  the  tubes.     It  requires  that  the 
glass  should  be  held  with  a  steady  hand,  and  perfectly  up- 
right, that  the  resulting  edge  may  be  flat.     Larger  vessels, 
as  jars,  &c.,  may  be  ground  in  a  similar  way,  but, are  better 
trusted  to  the  instrument-maker.  ^ 

1230.  When  a  bottle  requiring  a  stopper  has  been  fitted 
with  one  from  the  stopper  drawer  (25,  1222),  it  may  happen 
that,  though  nearly,  it  is  not  quite  true  and  tight.     In  such 
a  case  the  stopper  may  be  made  to  fit  accurately  by  being 
ground  with  a  little  sea-sand  or  coarse  emery  and  water,  into 
the  mouth  of  the  bottle,  during  which  operation  it  should  be 
quickly  inserted  into  and  removed  from  its  place,  and  turned 
at  the  same  time.     In  this  manner  the  glass  is  in  part  worn 
away  and  the  stopper  made  tight,  but  care  should  be  taken 
that,  during  the  grinding,  the  bottle  be  shifted  a  little  now 

*  In  this  process  the  hazard  is  nearly  entirely  obviated  by  keeping  the  file  wet. 
—ED. 


CLEANLINESS  AND  CLEANSING.  553 

and  then  in  the  hand,  that  different  parts  of  the  neck  and 
the  stopper  may  work  against  each  other  at  different  times, 
and  thus  mutually  correct  the  existing  inequalities. 


SECTION  XX. 

CLEANLINESS  AND  CLEANSING. 

1231.  MUCH  as  the  chemist  may  soil  his  fingers  during 
his  experimental  occupations,  he  will  soon  learn  the  great 
importance  of  cleanliness  to  the  success  of  his  experiments. 
The  regular  course  of  his  operations  causes  many  kinds  of 
matter  to  pass  in  succession  through  his  hands;  and  many 
of  the  substances  which  by  mixture  have  exhibited  the  phe- 
nomena they  were  competent  to  occasion,  and  so  far  an- 
swered the  purpose  of  the  experiment,  then  become  mere 
useless  dirt.     Their  dismissal  and  entire  removal,  when  thus 
circumstanced,  become  necessary,  that  they  may  not  con- 
taminate other  bodies;  and  are  as  imperatively  required,  as 
was  the  care  previously  bestowed  to  prevent  their  contami- 
nation from  extraneous  matter. 

1232.  It  is  this  rapid  change  in  the  character  and  relation 
of  the  substances  with  which  the  chemist  works,  that  makes 
a  constant  attention    to  cleanliness  essentially  necessary. 
The  very  bodies  which  at  one  moment  are  carefully  retained 
in  vessels  that  have  previously  been  cleansed  with  the  most 
scrupulous  attention,  become  the  next  in  the  situation  of  so 
much  dirt,  from  which  the  vessels  must  be  cleansed  as  per- 
fectly and  carefully,  before  they  can  be  fit  for  another  ex- 
periment, as  they  were  for  the  reception  of  the  now  rejected 
matter.     The  results  of  numerous  experiments  relative  to 
testing  bodies  in  solution  by  re-agents  are,  in  many  cases, 
dependent  on  the  employing  of  clean  vessels.     For  instance, 
a  portion  of  water,  examined  in  glasses  which  have  been 
carelessly  washed,  may  occasion  a  slight  precipitate  with 
nitrate  of  silver  or  muriate  of  baryta,  and  thus  seem  to  con- 

3U 


554  CLEANLINESS REGULATIONS. 

tain  a  sulphate  or  a  muriate ;  when  the  cause  of  the  precipi- 
tate may  be  nothing  more  than  portions  of  salts  adhering  to 
the  vessels. 

1233.  In  the  same  manner  the  purity  of  an  acid  or  a  test 
is  not  unfrequently  affected  by  the  state  of  the  bottle  con- 
taining it,  or  by  the  dirty  condition  of  glass  rods  dipped  into 
it,  or  of  the  funnels  through  which  it  has  been  poured  or 
filtered,  or  of  the  vessels  used  in  its  transference;  and  some- 
times it  is  contaminated  by  laying  the  stopper  of  the  bottle 
containing  it  in  a  dirty  place.     Nor  is  it  only  that  kind  of 
dirt  or  impurity  which  gives  an  evident  tinge  to  what  it  ad- 
heres to  that  is  to  be  avoided,  but  also  numerous  colourless 
substances,  as  salts,  solutions,  &c.;  and,  in  a  word,  anything 
which  differs  from  the  principal  substance  itself,  and  is  at 
the  same  time  liable  to  be  dissolved  or  mixed  with  it. 

1234.  In  consequence  of  these  liabilities,  and  their  inter- 
ference with  experiments,  it  should  be  established  as  a  gene- 
ral rule  in  the  laboratory,  that  no  apparatus,  nor  any  vessel 
(except  such  as  may  be  destined  to  a  particular  use,  and  is 
as  convenient  when  with  a  little  previously  adhering  matter 
as  if  it  were  clean),  be  put  away  in  a  dirty  state.     All  vessels 
or  instruments  when  resorted  to  should  be  found  fit  for  the 
nicest  experiment  to  which  they  are  applicable.     Glass  rods 
or  stirrers  should  be  preserved  in  a  clean  place ;  glasses  on 
a  clean  shelf;  and  stoppers  when  taken  out  of  bottles  should 
be  laid  upon  clean  glass  surfaces.     These  attentions  and 
regulations  will  be  found  always  useful,  at  times  essential. 
They  are  generally  more  requisite  and  influential  in  minute 
chemistry,  than  in  large  experiments;  and  in  trains  of  re- 
search, than  in  the  process  of  the  manufacturer. 

1235.  As  a  part  of  the  general  system  of  cleanliness,  the 
walls  and  ceiling  of  the  laboratory  should  be  lime-washed  at 
intervals,  dependant  on  the  nature  of  the  operations  per- 
formed in  it,  and  the  state  of  the  walls.     The  general  light 
of  the  place  will  by  this  means  be  increased;  and  the  surface 
thus  renewed  from  time  to  time  more  readily  absorbs  the 
fetid  odours,  animal  effluvia,  and  acid  fumes,  that  are  occa- 
sionally disengaged  during  chemical  operations.     The  tables 
and  the  filtering  stands  should  be  cleared  and  cleaned  once 


CLEANLINESS LABORATORY TROUGHS.  555 

a  week  or  a  month,  according  to  the  use  made  of  them. 
The  shelves  should  be  periodically  dusted,  and  the  bottles 
upon  them  wiped.  The  laboratory  drawers  should  also  be 
cleared  and  cleaned  from  time  to  time,  that  the  stirrers, 
valves,  corks,  and  other  articles  in  them  may  be  preserved 
in  a  proper  state  for  use.  All  dirty  glasses,  and  the  results 
of  experiments  when  done  with,  and  of  no  further  service, 
should  be  put  together  into  one  particular  place,  being  either 
a  tray  upon  the  table,  or  a  portion  of  the  table  appointed  for 
the  purpose;  and  no  substance  should  be  put  into  this  place 
that  is  not  to  be  thrown  away,  nor  any  glass  or  apparatus 
that  is  not  to  be  cleaned.  A  little  method  in  these  arrange- 
ments prevents  mistakes  and  errors;  very  much  facilitates 
the  laboratory  operations;  and  quickly  brings  every  thing 
into  a  ready  and  available  condition. 

1236.  When  the  japan  or  paint  of  the  pneumatic  trough 
is  either  wearing  or  pealing  away,  the  trough  should  be  emp- 
tied of  water,  dried,  and  the  surface  renewed.     The  water 
of  the  troughs,  which  are  preserved  full  for  constant  use, 
should  be  changed  every  fortnight  or  three  weeks,  or  oftener 
if  any  experiment  has  occasioned  its  contamination  more 
quickly.     If  alkali,  acid,  sulphuretted  hydrogen,  or  any  ex- 
traneous substance  likely  to  exert  a  chemical  action  upon,  or 
mixture  with  gases  that  may  be  standing  over  the  trough,  finds 
its  way  into  the  water,  it  should  immediately  be  changed. 
The  loose  iron  trivets  (733)  for  the  water  trough  should  be 
varnished  before  they  are  brought  into  use;  and  also  again 
at  any  future  time  when  rust  appears  upon  them,  or  if,  when 
put  into  the  water,  they  impart  a  yellow  tinge.     A  coat  or 
two  of  the  common  varnish,  called  Brunswick  black,  is  quite 
sufficient  to  prevent  the  contact  of  the  water  with  the  metal, 
as  well  as  oxidation.     A  better  coat,  as  being  more  adhesive, 
is  formed  upon  the  iron,  by  brushing  linseed  oil  over  it  when 
heated  just  below  visible  redness;  the  heat  decomposes  the 
oil,  and  leaves  the  iron,  when  cold,  covered  with  a  fine 
smooth  black  varnish,  adhering  very  closely,  and  effectually 
preserving  the  metal  from  contact  with  the  water. 

1237.  The  sink  and  its  importance  have  been  before  briefly 
noticed  (13):  it  is  essential  to  an  active  laboratory.    It  should 


556  THE  SINK ITS  ACCOMPANIMENTS. 

be  supplied  with  a  pail  and  a' pan,  or  large  vessel,  which,  be- 
ing constantly  full  of  water,  is  to  serve  in  turn  both  for  soak- 
ing and  rinsing  operations.  Several  nails  should  be  driven 
into  the  wall  over  the  sink,  upon  which  should  hang  various 
wires,  intended  to  facilitate  the  cleansing  processes.  Six 
or  eight  of  these  should  be  of  copper,  about  the  eighth  of  an 
inch  in  thickness,  from  twelve  to  eighteen  inches  in  length, 
bent  into  an  eye  at  one  end,  and  having  a  little  tow  wrapped 
round  them  at  the  other.  The  end  intended  to  hold  the  tow 
should  be  roughened,  by  being  struck  with  an  edge,  so  as  to 
have  a  few  teeth  cut  in  it,  or  by  having  a  notch  or  two  filed 
across  it,  that  the  tow  may  not  slip  off  when  it  is  pushed  up 
and  .down  a  tube,  or  through  a  narrow  aperture.  The  tow 
should  be  twisted  round  the  end  in  such  a  manner  as  to  hold 
by  these  irregularities.  Some  of  these  wires  should  be  quite 
straight,  others  curved  at  the  extremity,  that  they  may  reach 
parts  unattainable  by  the  straight  wire,  as  the  inside  of  a 
globe  or  retort,  or  that  part  of  a  bottle  which  is  close  to  the 
neck. 

1238.  A  similar  set  of  wires  of  less  thickness  should  be 
appointed  for  the  purpose  of  cleaning  sharp  angles,  narrow 
cavities,  and  small  apparatus,  for  which   the  thicker   wires 
would  be  too  large.     These  are  best  of  iron,  being  stronger 
when  of  equal  thickness  than  those  of  copper.     Some  of 
both  these  kinds  of  wires  should  be  retained  for  use   when 
their  tow  terminations  are  wetted,  others  for  dry  tow,  and 
others  without  any  tow  at  their  extremities,  that  they  may 
be  ready  for  the  removal  of  hard  adhering  matter. 

1239.  Besides  these  wires,  one  or  two  wiping  sticks  should 
be  provided,  for  the  purpose  of  drying  the  inside  of  long  jars, 
and  other  apparatus,  to  which  the  hand  cannot  have  access. 
They  should  be  of  a  tough  but  light  wood,  that  they  may 
have  strength  enough  to  resist  considerable  force,  and  yet 
not  endanger  the  glass  by  a  tap  or  a  slight  blow.     They 
should  be  about  two  feet  in  length;  not  round,  but  angular 
or  flat  at  the  end,  that  the  cloth  may  less  easily  slip  off;  and 
if  the  end  be  thinned  away  on  one  side,  so  as  to  be  wedge- 
shaped,  it  is  more  effectual  in  applying  the  cloth  with  force 
to  the  angular  space  at  the  bottoms  of  jars  or  bottles. 


CLEANSING  OF  VESSELS — GLASSES.  557 

1240.  The  necessary  supply  of  dusters,  cloths,  and   tow, 
should  be  furnished  to  the  sink,  each  having  its  respective 
place  both  in  the  clean  and  dirty  state. 

1241.  Cleansing   of  Vessels. —  Glasses.    In  by  far   the 
greatest  number  of  cases  glasses  are  dirtied  by  moist  sub- 
stances, as  precipitates  or  solutions ;  it  is  then  advantageous 
to  cleanse  them  immediately  upon  throwing  out  the  contents, 
and  before  the  dirt  can  dry  or  harden.     Rinsing  will  usually 
remove  the  whole  of  the  dirt;  or  if  it  adhere,  it  is  but  slightly, 
and  it  immediately  gives  way  when  touched  by  a  wire  with 
moist  tow.     If  it  should  resist  this  application,  a  similar  wire 
with  wet  tow,  aided  by  a  little  of  the  wood  or  charcoal  ashes, 
which  are  always  lying  at  the  bottom  of  some  of  the  furnaces, 
will  generally  remove  every  thing.     Sand  should  not  be  used 
for  these  purposes,  as  it  cuts  and  roughens  the  soft  flint  glass, 
of  which  vessels  are  made  in  England  ;  and  at  the  same  time 
that  it  injures  their  transparency,  it  renders  them  improper 
for  several  particular  experiments  of  precipitation.*     When 
by  any  of  these  methods  the  dirt  has  been  removed,  the  glass 
is  to  be  well  rinsed  in  clean  water,  turned  upside  down  for 
twelve  hours  on  a  side  shelf  or  table  to  drain,  and  then  wiped. 
The  wiping  should  be  performed  with  a  cloth  in  each  hand, 
not  only  because  a  cloth  is  more  cleanly  than  the  hand,  but 
that  if  the  glass  should  break  the  hand  may  be  defended. 
The  cloths  should  never  be  in   a  greasy,  resinous,  or  pitchy 
state;  but  so  clean,  that  without  communicating  any  thing 
they  will  remove  all  substances  that  can  be  wiped  off.    Labo- 
ratory cloths  when  clean  should  be  used,  first,  for  wiping 
glass,  then  for  wiping  tables  or  dirty  apparatus,  and  being 
once  so  used,  should  not  be  employed  for  clean  glass  again 
until  they  are  washed.     Especial  care  is  required  in  wiping 
glasses  that  the  inside  be  thoroughly  cleansed  in  every  part, 
for  it  is  with  that  part  of  the  vessel  that  tests  and  solutions 
come  in  contact. 

1242.  If  the  glasses  be  greasy  they  should  not  be  washed, 
but  in  the  first  place  wiped  with  tow  to  remove  as  much  as 

*  Bottle-washers  prefer  leaden  shot  to  any  other  substance  for  loosening  me- 
chanically adherent  dirt.  It  is  not  liable  to  the  objection  made  to  sand,  but  is 
not  a  safe  cleanser  of  thin  vessels,— ED. 


558  CLEANSING  OF  GLASSES TUBES. 

possible  of  the  grease,  and  then  a  dry  cloth  should  be  used, 
until  the  glass  appears  clean.  Its  surface  should- afterwards 
be  washed  with  a  little  strong  solution  of  alkali,  applied  by 
means. of  a  wire  and  tow;  this  removes  the  thin  film  of  grease 
remaining  after  the  wiping,  and  the  glass  may  then  be  rinsed, 
drained,  and  wiped,  as  before  directed.  A  duster  should  not 
be  used  at  random  for  these  greasy  glasses,  lest  it  should  the 
next  moment  be  applied  to  a  clean  vessel,  and  communicate 
impurities  to  it;  but  one  should  be  kept  apart  and  appropri- 
ated for  these  purposes. 

1243.  If  the  glass  be  soiled  by  resin,  turpentine,  resinous 
varnishes,  or  similar  bodies,  it  should  in  the  first  place  be 
washed  with  a  little  strong  solution  of  potash,  those  places 
where  the  resin  adheres  being  rubbed  by  means  of  a  wire 
and  tow,  until  the  alkali  has  softened  the  whole,  and  rendered 
it  soluble  in  or  moveable  by  water:  it  is  then  to  be  washed, 
rinsed,  and  dried,  as  before.     Or,  in  place  of  alkali,  a  little 
strong  sulphuric  acid  may  be  used,  and  is  sometimes  even 
more  advantageous:  being  poured  into  the  glass  or  vessel, 
the  latter  should  be  inclined  in  various  directions,  so  as  to 
bring  the  acid  into  contact  with  all  parts  of  the  foul  surface: 
it  will  become  very  black,  and  after  a  few  minutes  the  resin, 
&c.,  will  wash  off,  and  the  glass  may  be  cleaned  in  the  ordi- 
nary way. 

1244.  Pitch  and  tar,  when  they  adhere  to  glass,  may  in  part 
be  scraped  off.  A  little  strong  sulphuric  acid  applied  as  above, 
will  loosen  and  separate  the  remainder.     Occasionally  a  little 
oil  may  be  used;  being  rubbed  on  the  soiled  parts,  it  mixes 
with  and  softens  these  adhesive  substances,  so  that  they  may 
be  wiped  off  by  tow,  and  then  the  glass  is  to  be  cleaned  from 
the  oil  as  before  described. 

1245.  Tubes  are  cleansed  generally  in  the  same  manner 
as  glasses.     Wires  with  tow  will  be  found  very  convenient 
in  displacing  solid  and  adhering  dirt  from  their  insides.    The 
tubes  should  be  well  rinsed  twice  or  thrice,  being  each  time 
half  filled  with  water,  closed  by  the  finger,  and  then  well 
shaken.     They  may  be  turned  upside  down,  and  left  inclining 
against  each  other  in  a  corner  to  drain ;  after  some  hours 
they  may  either  be  wiped  dry  within  by  a  cloth  and  stick, 


CLEANSING  OF  AIR  JARS BASINS.  559 

or,  what  is  perhaps  more  convenient,  left  with  their  mouths 
open  to  the  air  until  the  interior  has  become  dry  by  evapo- 
ration, and  then  be  wiped  to  remove  any  dust  which  may 
have  entered.     Tow  is  not  a  good  substance  for  the  removal 
of -water  from  glass  surfaces,  and  for  tubes  it  is  better  to  use 
a  long  slip  of  cloth,  two  or  three  inches  wide.     Having  in- 
troduced a  few  inches  in  length  of  this  slip  into  the  tube,  the 
wire  or  stick  is  to  be  inserted,  and  the  cloth  thrust  up  to  the 
extremity,  so  as  to  form  an  accumulation  there;  the  rest  of 
the  tube  will  then  be  occupied  bya  wire  or  stick,  and  a  part 
of  the  slip  of  cloth.     It  will  thus  be  found  easy  by  a  very  lit- 
tle management,  and    a  rotary  and  longitudinal  motion  of 
the  tube,  to  wipe  every  part  of  the  inside  clean  and  dry,  in 
an  expeditious  and  perfect  manner. 

1246.  Long  tubes  open  at  both  ends,  which  have  become 
dusty,  are  easily  wiped  by  pushing  a  loose  pellet  of  cloth  or 
tow,  up  and  down  them  by  a  long  stick:  or  a  piece  of  string, 
having  a  loop  at  the  end  into  which  some  tow  has  been  in- 
troduced, may  be  used  to  draw  the  tow  through  the  tube,  and 
thus  to  wipe  it  clean.     This  is  a  very  useful  mode  of  clean- 
ing out  bent  tubes  open  at  both  ends;  the  end  of  the  string 
may  be  readily  passed  through  them,  by  attaching  a  little 
piece  of  wire  to  it  as  a  weight.     The  piece  of  string  must 
be  longer  than  the  tube  to  be  wiped,  and  the  portions  of 
tow  used  at  first,  should  be  such  as  will  easily  pass  the  an- 
gles; they  may  be  increased  in  size  by  the  addition  of  more 
tow  if  necessary. 

1247.  Air  jars   require  no  further  directions  for   their 
cleansing   than    is  given  with  respect  to  glasses   (1241). 
When  of  such  narrow  dimensions  as  not  to  admit  the  hand, 
the  insides  must  be  wiped  in  the  same  manner  as  has  just 
been  described  for  tubes  (1246).     Generally  in  these  cases 
abundance  of  cloth  should  be  allowed  to  enter  the  vessel 
before  the  stick,  that  the  mass  thrust  up  to  the  extremity 
may  be  large,  and  bear  uniformly  against  the  glass  over  a 
considerable  surface. 

1248.  Evaporating  basins  are  very  easily  washed.     The 
soaking  tub  (1237)  is  useful  for  the  softening  and  removing 
of  most  substances,  which  are  likely  to  accumulate  in  them. 


560  CLEANSING  OF  FLASKS. 

Grease,  resin,  and  similar  bodies,  may  be  removed  by  tow 
and  damp  ashes,  or  soft  sand,  or  otherwise  by  a  little  strong 
sulphuric  acid  (1243).  When  all  dirt  is  removed,  the  basins 
should  be  rinsed,  turned  upside  down  to  drain,  and  then 
wiped.  It  is  advisable  to  clean  the  stock  of  evaporating 
basins  belonging  to  the  laboratory  once  every  two  or  three 
months,  with  a  little  strong  solution  of  alkali,  both  inside 
and  outside,  rejecting  at  such  times  those  which  have  be- 
come useless. 

1249.  Flasks  are  not  so  easily  cleansed  as  the  vessels 
already  mentioned,  from  the  greater  difficulty  of  access  to 
the  interior;  but  the  bent  wires  referred  to  (1237)  will  over- 
come many  obstacles.     Florence  flasks  are  frequently  oily 
when  obtained  from  the  Italian  or  wine  warehouses.     They 
may  be  readily  cleansed  by  putting  a  little  strong  nitric  acid 
into  each,  and  heating  it  over  a  lamp  or  sand  bath,  after 
which  every  thing  will  wash  out  with  water.     Strong  sul- 
phuric acid  may  be  used  for  the  same  purpose,  being  brought 
into  contact  with  every  part  of  the  glass,  without  requiring 
the  application  of  heat.     Either  acid  is  better  than  solution 
of  alkali.     If  metallic  matter  adhere  to  the  inside,  a  little 
nitro-muriatic  acid  introduced,  and  heated  on  the  place,  sel- 
dom fails  of  separating  and  removing  the  substance.     When 
the  impurity  is  loose  or  separable  by  water,  the  flasks  should 
be  well  rinsed  and  inverted  on  a  filtering-stand  (528)  or 
shelf  (15),  left  to  drain  for  half  an  hour,  then  well  rinsed  out 
with  distilled  water,  and  again  placed  to  drain. 

1250.  When  the  impurity  within  flasks,  globes,  or  similar 
vessels,  adheres  mechanically,  and  is  not  soluble  in  water, 
it  may  frequently  be  effectually  loosened  and  removed  by 
introducing  some  coarse  brown  paper  torn  into  fragments 
about  an  inch  square,  with  water  enough  to  half  fill  the  ves- 
sel, and  agitating  the  whole  vigorously.     The  pieces  of  paper 
will  rub  or  break  off  dirt  that  has  resisted  the  action  of  water 
alone,  and  most  sediments  or  deposits  may  be  thus  removed. 
The  addition  of  a  few  wood-ashes  increases  the  effect. 

1251.  Upon  wiping  the  exterior  of  globular  vessels,  those 
which  are  thin,  as  Florence  flasks,  require  care,  lest  they  be 
crushed  to  pieces  between  the  hands.     It  may  be  necessary 


CLEANSING — DRYING — RETORTS.  561 

to  dry  the  interior  of  some  of  them,  but  others  will  not  need  it. 
When  they  are  to  be  dried,  they  may  be  left  on  the  retort 
shelf  in  the  cupboard  (14),  or  on  the  filtering-stand,  with  the 
mouth  downwards,  until  the  water  within  has  evaporated; 
but  as  this  will  require  some  days  or  weeks,  a  more  rapid 
method  may  occasionally  be  adopted.  This  is  to  warm  the 
flask,  so  as  to  convert  the  water  within  into  vapour,  and  then  by 
introducing  one  end  of  a  piece  of  glass  tube,  whilst,  the  other 
is  held  by  the  hand  against  the  nozzle  of  a  pair  of  bellows,  to 
blow  out  the  moist  air,  and  replace  it  by  that  which  is  dry. 
If  the  first  warming  be  insufficient  to  convert  all  the  water 
into  vapour,  the  flask  may  be  heated  a  second  time;  or  if  the 
flask  be  thick,  and  retain  its  temperature  for  some  minutes, 
merely  persisting  in  blowing  air  through,  will  gradually 
evaporate  and  remove  the  water  from  within. 

1252.  Instead  of  using  the  bellows,  the  mouth  will  answer 
every  purpose;  for  if,  when  the  flask  is  hot,  the  external  end 
of  the  tube  be  put  between  the  lips,  it  will  be  easy  to  throw 
air  in  from  the  lungs,  which,  though  it  contain  moisture,  is 
much  drier  than  that  in  the  flask.  When  the  appearance  of 
liquid  within  no  longer  exists,  the  moist  air  last  introduced 
from  the  lungs  is  easily  removed  by  drawing  air  out  of  the 
flask,  through  the  tube,  into  the  mouth;  other  portions  then 
enter  to  replace  it,  and  the  vessel  is  left  filled  with  an  atmos- 
phere of  ordinary  dryness. 

1253;  Six  or  eight  Florence  and  other  flasks  should  be 
kept  ready  for  use  on  the  filtering-stand;  the  mpuths  of  the 
rest  should  be  covered  up  with  paper  to  keep  the  dust  out, 
and  be  put  aside  until  wanted.  In  thus  guarding  the  mouth 
of  a  flask,  retort,  tube,  or  similarly  formed  apparatus,  it  is 
merely  necessary  to  roll  a  slip  of  paper  round  the  end,  so 
that  it  shall  project  sufficiently  beyond  the  edge,  and  then 
to  fold  or  double  this  projecting  part  down,  in  such  a  man- 
ner as  to  close  the  mouth,  and  at  the  same  time  prevent  the 
slip  from  unrolling. 

1254.  Retorts  may  be  cleaned  according  to  the  directions^ 
just  given  for  flasks  (1249),  but  if  tubulated  they  require 
more  care,  because  of  the  increased  tendency  to  crack  and 
fly  at  the  junctions.     When  rinsed  they  should  be  carefully 
3V 


562  CLEANSING  BOTTLES REMOVING  STOPPERS. 

placed,  so  that  the  water  which  drains  may  run  quite  out  of 
the  vessel.  When  warmed  for  drying  (1251),  attention  must 
be  paid  Jo  the  tubulature,  that  it  be  not  suddenly  heated  or 
cooled.  It  is  necessary  too  that  drops  of  water  be  not 
allowed  to  run  from  a  cool  upon  a  hot  part,  as  they  might 
occasion  fracture. 

1255.  Bottles.     The  bottles  of  the  laboratory  require  con- 
stant attention  and  cleansing.     They  are  liable  to  accidents 
and  uses  of  all  kinds,  and  are  soiled  by  every  species  of 
matter  in  turn.     Now  and  then  the  stoppers  of  bottles  be- 
come fixed  (741),  in  which  case  means  of  loosening  them, 
successively  increasing  in  power  (but  also  unfortunately  in 
danger),  must  be  resorted  to,  until  the  stopper  is  removed, 
or,  giving  way,  is  destroyed.     One  of  the  simplest  methods 
when  the  unaided  hands  fail,  is  to  tap  the  stopper  alternately 
on  opposite  sides,  with  a  piece  of  wood,  as  the'  handle  of  a 
brad-awl  or  a  chisel,  the  other  part  of  the  tool  being  held 
loosely  in  one  hand,  whilst  the  bottle  is  retained  lightly  at 
its  lower  part  in  the  other.     The  light  alternate  concussions 
on  the  opposite  sides  of  the  stopper  are  often  sufficient  to 
destroy  the  adhesion   between  it  and  the  bottle.     This  is 
indicated  by  the  sound;  for  so  long  as  the  adhesion  remains 
perfect,  the  noise  made  by  the  tap  is  as  if  the  bottle  and 
stopper  were  but  one  piece  of  matter;  but  the  moment  the 
stopper  is  loosened,  however  slightly,  the  character  of  the 
sound  changes,  becoming  somewhat  flatter  and  heavier,  and 
then  a  few  more  taps  complete  the  operation,  and  the  stop- 
per gives  way  to  the  hand.     Before  thus  endeavouring  to 
loosen  the  stopper,  the  thickness  of  the  neck  by  which  its 
upper  and  lower  parts  are  connected  should  be  observed :  if 
that  be  very  small,  the  force  must  be  carefully  applied;  if 
strong,  a  little  more  liberty  may  be  taken  with  it.     If  the 
stopper  does  not  soon  give  way,  this  means  alone  will  not 
be  sufficient  for  its  removal. 

1256.  Another  method  of  removing  a  bottle-stopper  is  to 
insert  its  head  into  a  chink,  and  then  endeavour  to  turn  the 
bottle  with  the  hands.     This  kind  of  force  is  similar  to  that 
exerted  by  the  hand  upon  the  stopper,  but  is  more  powerful; 
and  if  the  neck  of  the  stopper  break,  the  hand  is  out  of  the 


REMOVING  STOPPERS.  563 

way  of  danger.  An  upright  board,  such  an  one  as  supports 
the  ends  of  a  set  of  shelves,  should  be  selected  in  a  con- 
venient situation  in  the  laboratory,  and  a  vertical  slit  cut 
through  it  about  a  foot  in  length,  an  inch  in  width  above, 
but  gradually  decreasing  in  size,  so  as  to  be  about  the  third 
of  an  inch  at  the  bottom.  The  top  of  the  hole  may  be  about 
the  height  of  the  breast.  This  aperture  will  in  one  part  or 
another  receive  and  retain  the  head  of  almost  any  stopper, 
and  prevent  it  from  turning  with  the  bottle.  Then,  by  wrap- 
ping a  cloth  about  the  bottle,  and  grasping  it  in  both  hands, 
the  attempt  to  turn  it  round  so  as  to  move  the  stopper  may 
be  made,  with  any  degree  of  force  which  it  may  be  thought 
safe  to  exert.  If  the  force  be  such  as  to  occasion  fracture, 
it  will  generally  occur  at  the  neck  of  the  stopper,  twisting 
the  head  from  the  plug.  It  is  only  when  the  bottle  is  wide- 
mouthed,  the  stopper  consequently  having  great  surface  of 
adhesion,  and  the  neck  of  the  stopper  is  also  very  thick,  that 
there  is  any  risk  of  the  bottle  breaking  in  the  hand.  But 
the  force  employed  should  never  be  carried  so  far  as  to  cause 
fracture  any  where;  the  attempt,  if  unavailing  with  the  ap- 
plication of  a  moderate  power,  should  be  desisted  from. 

1257.  Another  and  a  very  successful  method  of  removing 
a  stopper  is,  to  turn  the  bottle  round,  when  held  horizon- 
tally over  the  small  flame  (199)  of  a  spirit-lamp  or  candle 
applied  to  the  neck.  The  heat  should  be  applied  only  to  the 
part  round  the  plug  of  the  stopper,  and  in  a  few  moments, 
when  that  has  become  warm,  the  stopper  should  be  tapped 
with  the  piece  of  wood  as  before  (1255).  The  application 
of  the  heat  expands  the  neck  of  the  bottle,  and  rendering  it 
larger,  permits  the  removal  of  the  stopper  to  be  effected  by 
a  force  previously  quite  insufficient.  As  soon  as  the  stopper 
moves  by  tapping,  it  is  to  be  taken  out,  and  must  not  be  re- 
placed until  the  glass  is  cold.  The  application  of  heat  in 
this  manner  must  be  short,  and  the  operation  altogether,  to 
be  successful,  must  be  a  quick  one;  for  it  is  obvious  that 
the  effect  depends  upon  the  difference  of  temperature  be- 
tween the  stopper  and  the  neck ;  and  if  the  former  become 
heated  as  well  as  the  latter,  no  good  result  can  be  expected, 


564  STOPPERS — METHODS  OF  LOOSENING  THEM. 

and  the  bottle  is  endangered  by  the  application  of  heat  to  no 
good  purpose. 

1258.  If,  when  the  neck  has  thus  been  warmed,  the  bottle 
is  held  upright,  and  struck  smartly  upon  the  bottom  with  the 
palm  of  the  hand,  it  will  frequently  occasion  the  displacement 
of  the  stopper;  and  the  method  is  advantageous  when  the 
bottle  contains  fluid;  but  precautions  must  be  taken  that  the 
stopper  do  not  fall  back  on  to  the  bottle  and  break  it,  or  into 
any  other  situation  to  do  harm. 

1259.  If  the  contents  of  the  bottle  are  fluid,  it  should  be 
held  so  inclined  that  they  may  not  become  heated;  if  they 
are  volatile  this  method  should  be  tried  very  carefully,  lest 
the  vapour  formed  within  should  burst  the  bottle.     The  ap- 
plication of  heat  in  this  way  is  seldom  successful  unless  im- 
mediately so;  and  there  is  always  some  risk  of  .cracking  the 
neck  of  the  bottle. 

1260.  It  has  occasionally  been  recommended  to  apply 
heat  to  the  neck,  not  by  a  flame,  but  by  means  of  the  friction 
of  a  long  piece  of  list  passed  once  round  the  part,  and  then 
drawn  to  and  fro.     The  plan  may  be  occasionally  useful, 
especially  where  liquids  are  enclosed,  but  has  its  disadvan- 
tages. 

1261.  It  is  often  advantageous  to  put  a  little  olive  oil 
round  the  edge  of  the  stopper  at  its  insertion,  allowing  it  to 
soak  in  for  a  day  Or  two.     If  this  be  done  before  the  heat  be 
applied,  it  frequently  penetrates  with  increased  facility  at  the 
time  of  heating;  by  oil,  heat,  and  tapping,  very  obstinate 
stoppers  may  be  removed.     When  a  stopper  has  been  fixed 
by  a  crystallization  from  solution,  water  will  sometimes  set 
it  free,  and  it  is  more  advantageous  in  such  cases  than  oil, 
because  it  dissolves  the  cement.     When  the  cementing  mat- 
ter is  a  metallic  oxide  or  a  sub-salt,  a  little  muriatic  acid 
may  be  useful,  if  there  be  no  objection  to  its  application, 
arising  from  the  nature  of  the  substance  within. 

1262.  The  preceding  are  all  quick  operations,  and  one  or 
other  of  them  will  generally  loosen  a  tight  stopper,  and  save 
the  bottle  with  its  stopper  and  contents.     If  they  fail,  the 
following  method  may  be  tried,  which  is  particularly  success- 
ful in  cases  where  stoppers  are  forced  inwards  by  atmospheric 


STOPPERS  REMOVED  FROM  JARS.  565 

pressure,  in  consequence  of  internal  absorption  ;  the  preced- 
ing methods  often  make  such  cases  worse.  A  piece  of  strong 
twine  is  to  be  doubled,  and  a  knot  tieckso  as  to  form  a  loop 
of  about  four  inches  in  length.  The  knot  is  to  be  brought 
close  to  the  neck  of  the  stopper,  the  two  ends  passed  round, 
so  as  to  meet  on  the  opposite  side,  and  tied  there  tightly,  so 
as  to  fasten  the  string  securely  round  the  neck.  The  two 
strings  are  then  to  be  tied  together,  so  as  to  form  a  loop  on 
that  side  the  stopper  equal  in  length  to  the  first  loop,  or 
about  four  inches.  These  loops  now  serve  as  handles  by 
which  to  pull  at  the  stopper;  and,  being  on  opposite  sides, 
permit  the  force  to  be  applied 'so  as  to  draw  the  stopper 
directly  forward  out  of  the  neck  of  the  bottle.  For  this  pur- 
.  pose  they  are  to  be  passed  over  a  fixed  bar  (if  horizontal,  so 
much  the  more  convenient),  and  are  to  be  placed  about  two 
and  a  half  or  three  inches  apart  on  the  bar,  that  by  directing 
the  pull  on  the  bottle  a  little  on  one  side  or  the  other,  the 
strain  upon  the  stopper  may  be  equal  or  nearly  so  on  the  two 
sides.  A  cloth  is  now  to  be  wrapped  about  the  bottle,  the 
hand  being  applied  round  the  neck,  and  the  bottle  is  to  be 
pulled  steadily.  During  the  endeavour  to  separate  it  from 
the  stopper,  the  latter  myst  be  struck  gently  on  each  side 
with  the  piece  of  wood,  as  before  directed  (1255).  The 
force  with  which  the  bottle  is  pulled  must  be  increased  until 
the  stopper  either  gives  way,  or  the  power  has  been  increased 
unavailingly  to  such  a  degree  .as  to  excite  fear  that  the  bot- 
tle itself  may  break  in  the  effort.  But  generally,  long  before 
this  fear  need  be  entertained,  the  stopper  will  leave  its 
place,  and  the  operation  will  consequently  have  succeeded. 
It  is  necessary  to  be  cautious,  that  as  the  stopper  leaves  the 
neck  and  falls  down  suspended  only  by  the  string,  it  shall  not 
swing  against  any  thing  so  hard  as  to  occasion  its  fracture; 
this  is  easily  done  by  pu.tting  a  cloth  or  duster  to  receive  it. 
1263.  When  stoppers  become  fixed  in  the  necks  of  jars 
(741),  they  are  generally  removed  with  great  facility  by  hit- 
ting them  from  beneath  with  the  end  of  a  stick,  which  tends 
directly  to  force  them  out  of  their  places;  few  stoppers  will 
resist  this  advantageous  application  of  mechanical  power. 
The  stick  should  be  a  solid  and  rather  heavy  one,  but  not  so 


566  CLEANSING  OF  BOTTLES. 

hard  as  to  endanger  the  glass.  The  end  of  the  handle  of  a 
hammer  answers  very  well  for  the  purpose,  the  head  of  the 
hammer  adding  to  the%  momentum  and  steadiness  of  the  blow. 

1264.  If  the  stopper  will  not  give  way  to  any  of  these  me- 
thods, then  all  that  can  be  done   is  to  remove  it  piecemeal. 
Large  stoppers  are  often  made  hollow,  to  diminish  their 
weight;  the  heads  of  these  may  be  broken  off,  when  their 
plugs  are  easily  penetrated  by  a  pointed  file,  and  thus  may 
be  separated  without  loss  of  the  bottle.     But  if  the  stoppers 
are  solid,  it  is  only  by  grinding  that  they  can  be  removed; 
this  is  the  work  of  the  glass-cutter,  and  the  value  of  the  bot- 
tle is  seldom  equal  to  the  expense  and  the  risk.     The  bottles 
of  which  the  stoppers  have  been  successfully  broken  out,  must 
be  refitted  with  others  from  the  stopper-drawer  (25,  1222,. 
1230). 

1265.  All  the  agents  and  methods  for  cleaning  glass  al- 
ready referred  to,  are  required  occasionally  for  the  cleansing 
of  bottles.     The  stoppers  should  be  cleaned  at  the  same 
time;  and  when  acids  or  alkalies  are  applied  to  the  bottles, 
a  little  should  be  allowed  to  flow  about  the  stoppers  when 
in  their  places,  and  the  latter  then  worked  in  the  neck  for  the 
purpose  of  rubbing  off  the  impurity,  and  bringing  it  more 
freely  into  contact  with  the  dissolving  or  detaching  agent. 
When  all  foulness  is  dissolved  or  washed  away,  the  bottles 
should  be  drained,  rinsed  in  distilled  water,  drained  again, 
and  then  wiped ;  and,  if  necesgary,  dried  within,  by  warming 
and  blowing  air  through  them  (1251).     This  must  be  done 
with  more  caution  than  is  necessary  for  flasks,  because  of 
the  greater  irregularity  in  thickness  and  form  of  these  vess- 
els.    Finally,  the  stoppers  are  to  be  replaced,  a  little  tallow 
or  yellow  wax  being  put  round  them  in  the  manner  already 
described  (433,  741). 

1266.  If  the  laboratory  be  in  daily  use,  these  washings 
and  cleansings  of  glass  should  be  performed  every  evening, 
the  apparatus  being  left  to  drain  during  the  night,  and  then 
wiped  on  the  following  morning.     Such  a  practice  will  be 
found  at  least  very  useful  and  convenient,  and  the  vessels 
will  be  ready  for  service  at  all  ordinary  hours  of  experiment. 
The  open  apparatus,  such  as  glasses,  jars,  &c.,  should  be 


CLEANSING  COPPER PLATINUM— MORTARS.  567 

put  by  in  their  respective  places,  with  their  mouths  down- 
wards, to  exclude  dust. 

1267.  When  oxidized  and  foul  copper,  such  as  wires, 
plates,  &c.,  is  rubbed  clean  by  sand-paper,  a  subtle  cupre- 
ous dust  is  diffused  through  the  air,  which  is  exceedingly  un- 
pleasant in  its  effects  upon  the  mouth  and  nostrils.     It  is  bet- 
ter in  such  cases  to  use  a  little  water  with  the  sand-paper; 
the  copper  is  more  readily  cleaned,  and  all  unpleasant  effects 
are  prevented.     Foul  copperplates  may  be  cleaned  also  by 
putting  them  into  the  furnace  and  heating  them  to  redness 
for  five  minutes,  with  access  of  air,  so  as  to  allow  the  forma- 
tion of  a  coat  of  oxide  upon  them,  and  then  plunging  them  in 
water.     The  oxide  scales  off,  or  may  easily  be  separated  by 
bending  the  plate,  and  leaves  the  latter  clean  and  metallic. 

1268.  When  a  platinum  crucible  has  become  tarnished 
and  dirty  by  use,  in  consequence  of  the  adhesion  of  sub- 
stances, it  is  perhaps  best  cleaned  by  making  it  red  hot  in  a 
charcoal  fire,  and  sprinkling  over  it  a  powdered  mixture  of 
equal  parts  of  borax  and  salt  of  tartar,  or  carbonate  of  pot- 
ash.*    This  flux  fuses  over  the  surface  of  the  platinum,  and 
dissolves  most  earthy  or  metallic  impurities,  so  that  when, 
after  ignition  for  a  quarter  of  an  hour,  the  crucible  is  thrown 
into  water  and  left  there,  the  flux  dissolves  and  removes  all 
impurity  with  it.     It  is  assumed  that  the  crucible  has  been 
used  fairly,  and  is  soiled  only  by  adhering  oxide  of  iron  or 
other  substance.     If  metal  has  by  any  means  come  in  con- 
tact with  the  platinum,  the  ignition  will  only  do  harm  by 
making  the  alloy  of  the  metal  and  the  platinum  more  com- 
plete.    In  such  case,  if  the  injury,  i.  e.  the  contact  of  the 
extraneous  metal  with  the  platinum  be  slight,  it  may  be  well 
to  dissolve  the  former  by  a  little  nitric  acid  and  heat ;  but  if 
heat  has  been  long  applied,  and  the  alloy  be  formed  to  a 
considerable  extent,  nothing  remains  but  to  use  the  crucible 
for  the  few  purposes  to  which  it  may  yet  be  applicable  until 
it  becomes  unserviceable. 

1269.  Porcelain  and  other  mortars  should  be  kept  in  good 
and  clean  condition;  dry  pulverizations  frequently  fill  the 
minute  irregularities  of  the  inner  surfaces  with  the  substance 

*  WoHastoo, 


568  CLEANSING  THE  MERCURIAL  TROUGH. 

pulverized,  so  that  even  after  careful  washing,  portions  still 
remain  behind.  This  may  readily  be  observed  with  coloured 
bodies,  as  oxide  of  iron,  Prussian  blue,  vegetable  substances, 
&c.  A  little  sand  and  water  put  into  the  mortar  and  rubbed 
with  the  pestle  over  all  the  contaminated  parts,  cleans  them 
and  the  pestle  itself  so  far,  that  the  affusion  of  water  is  suf- 
ficient to  wash  off  all  impurities.  In  some  cases,  sulphuric 
or  nitric  acid,  or  solution  of  alkali,  must  be  used ;  their  action 
is  always  facilitated  by  rubbing  a  little  sharp  sand  at  the 
same  time  in  the  mortar  with  the  pestle*. 

1270.  There  is  one  apparatus  which  has  not  as  yet  been 
mentioned  in  this  chapter,  but  which  requires  frequent  atten- 
tion relative  to  its  state  of  cleanliness.     This  is  the  mercurial 
trough  (736,  782).     It  should  be  covered  when  out  of  use, 
that  dirt  and  dust  may  not  have  access.     If  these  be  allowed 
admission,  they  do  not  merely  collect  upon  the  surface  of  the 
metal,  but  by  the  mechanical  motions  to  which  the  mass  is 
subjected,  are  often  carried  beneath,  and  are  lodged  and  re- 
tained between  the  mercury  and  the  trough  even  at  the  very 
bottom  of  the  bath.     For  this  reason,  when  a  trough  has 
been  exposed  to  dirt  and  dust,  it  is  not  sufficient  to  clean 
only  the  surface  with  a  card,  but  the  mercury  should  be 
poured  out,  the  trough  well  wiped  and  cleaned  in  every  part, 
and  the  metal  restored,  after  it  also  has  been  cleaned  and 
purified. 

1271.  The  mercury  may  require  to  be  cleansed  both  from 
mechanical  and  chemical  impurities;  and  indeed   the  ordi- 
nary operations  of  the  pneumatic  trough  tend  to  confer  both 
these  contaminations.     The  processes  to  be  adopted  for  the 
removal  of  extraneous  matters  must  therefore  be  varied,  and 
several  very  different  in  principle  have  been  devised. 

1272.  Adhering  dirt  and  dust,  as  well  as  the  thin  films  of 
oxide  and  other  impurities  which  attach  to  mercury,  may  be 
removed  in  several  ways.     A  very  common  method  is  to  fold 
a  piece  of  paper  into  a  cone,  so  as  to  make  it  nearly  tight  at 
the  apex,  and  to  pass  the  mercury  through  it  as  through  a 
funnel.     The  aperture  at  the  bottom  may  be  made  larger  or 
smaller  by  a  little  management  of  the  paper :  when  the  in- 
ward fold  is  pulled  upwards,  it  increases  the  aperture  below, 


MERCURY  CLEANSED  FROM  IMPURITIES.  569 

whilst  pulling  the  outer  folds  upwards  a  little,  tends  to  close  it. 
The  aperture  may  also  be  opened  or  closed  more  or  less  by 
applying  the  finger  to  it.  The  mercury  as  it  runs  through 
should  be  received  in  a  glass  or  other  proper  vessel,  and  the 
last  portions  reserved  in  the  cone;  they  will  be  found  to 
abound  with  scum  and  other  impurities,  a  portion  of  which 
might  pass  out  with  the  metal.  It  is  better  to  put  these 
latter  portions  by  themselves,  and  when  they  have  accumu- 
lated, to  purify  them  altogether.  This  method  of  cleansing 
mercury  is  a  ready  and  sufficient  one  in  numerous  cases 
where  it  is  only  the  adhering  dirt  that  is  to  be  removed. 

1273.  Some  persons  recommend  that  the  mercury  should 
be  cleansed  from  mechanical  dirt  by  being  filtered  through 
the  pores  of  a  piece  of  hazel  wood  by  means  of  atmospheric 
pressure.     Others  squeeze  it  through  a  piece  of  chamois 
leather.     But  when  cleaned  by  any  of  these  methods,  a  film 
still  generally  adheres  to  its  surface;  and  the  metal  when 
agitated  has  a  scum  formed  upon  it,  especially  when  chemi- 
cally foul*.     Much  assistance  in  removing  this  exterior  scum 
and  dirt  is  gained  by  pulverizing  some  loaf  sugar,  putting  it 
into  a  bottle  with  the  mercury  to  be  cleansed,  and  agitating 
them  well  together.     The  sugar  should  be  damped,  which 
may  be  done  by  breathing  into  the  bottle  two  or  three  times; 
by  agitation  it  then  adheres  to  the  dirt  present,  and  the  mer- 
cury, being  removed  by  passing  it  through  a  paper  funnel,  is 
obtained  in  a  state  of  great  comparative  cleanliness. 

1274.  The  chemical  impurities  of  mercury  consist  of  cer- 
tain metals,  such  as  lead,  tin,  zinc,  &c.     These  interfere  che- 
mically when  the  metal  is  to  be  used  in  forming  combina- 
tions; and  from  the  rapidity  with  which  they  oxidate  and  pro- 
duce films  on  the  surface  (789),  interfere  mechanically  in  its 
uses  in  the  bath,  in  certain  electro-magnetic  experiments, 
and  in  the  construction  of  thermometers  and  barometers. 
Mercury  which  is  chemically  impure  will  soon  acquire  ad- 
hesive films  on  its  surface,  even  when  cleared  of  mechanical 

*  The  filter,  among  the  'best  and  readiest,  is  a  silk  handkerchief  folded  so  as  to 
be  double  or  triple.  By  a  little  pressure  the  mercury  passes  through  compara- 
tively clean  and  bright. — ED. 

3  W 


570  MERCURY  PURIFIED  BY  ACIDS. 

impurities,  and  with  a  rapidity  dependent  on  the  agitation  of 
the  metal  or  extension  of  its  surface. 

1275.  The  first  method  of  purifying  mercury  from  these 
metals  is  by  distillation.     The  operation  should  be  performed 
in  an  iron  retort,  a  portion  of  clean  iron  and  copper  filings 
having  been  introduced  with  the  mercury,  which  should  be 
condensed  and  received  in  clean  water.     Although  this  is  an 
excellent  process  generally,  yet  it  is  by  no  means  unobjec- 
tionable, for  both  zinc  and  arsenic  will  pass  over,  and  these 
metals  are  not  uncommonly  introduced  in  experiments  at 
the  mercurial  trough. 

1276.  A  very  useful  method  of  cleaning  considerable  quan- 
tities of  trough  mercury  is  to  put  from  half  an  inch  to  an  inch 
in  depth  into  a  large  earthenware  pan  (the  pneumatic  trough 
before  referred  to  (732)  answers  very  well  for  this  purpose), 
and  to  pour  over  it  sulphuric  acid  diluted  with  twice  its 
weight  of  water.     The  surface  of  contact,  and  consequently 
of  depuration,  is  thus  rendered  very  large.     The  substances 
should  be  left  together  for  a  week  or  two  at  common  tempe- 
ratures, being  frequently  agitated.     At  the  end  of  that  time 
the  metal  and  the  acid  are  to  he  separated,  the  latter  pre- 
served for  a  similar  operation  at  some  future  period,  and  the 
former  washed,  dried,  and  cleansed  mechanically,  as  already 
described  ( 1272,  &c.).     The  sulphuric  acid  acts  more  readily 
if  a  little  sulphate  of  mercury  be  added  to  it;  the  residue  of 
a  process  for  the  preparation  of  sulphurous  acid  from  'sul- 
phuric acid  and  mercury  may  be  used  for  the  purpose  with- 
out further  preparation.     This  residue  is  not  an  uncommon 
one  in  the  laboratory  (448),  and  being  put  altogether  into 
the  pan,  the  mercury,  the  sulphuric  acid,  and  the  sulphate 
of  mercury  present  in  it,  will  each  be  economically  and  use- 
fully disposed  of. 

1277.  An  acid  solution  of  nitrate  of  mercury  left  upon 
the   trough-metal    in   a   manner    similar   to  that  just   de- 
scribed, will  also  cleanse  it  to  a  great  extent  from  other 
metals.     The  solution  need  not  be  very  strong  or  in  large 
quantity ;  a  week  or  two  at  common  temperature  is  sufficient 
for  the  purpose.     The  solution,  when  poured  off,  should  be 
reserved  apart  from  other  nitrate  of  mercury,  for  this  parti- 


MERCURY FILMS  ON  IT — EFFECT.          571 

cular  use;  the  impurities  which  it  has  received  from  the  me- 
tal, and  for  which  it  has  given  up  an  equivalent  portion  of 
mercury,  rendering  it  unfit  for  any  other  than  very  ordinary 
purposes. 

1278.  These  chemical  cleansings  of  the  trough-mercury 
are  intended  to  destroy  the  disposition  which  exists  in  im- 
pure mercury  to  form  films  upon  its  surface.     The  films  are 
produced  by  the  oxidation  of  a  very  minute  portion  of  the  im- 
pure metal;  they  do  not  consist  of  oxide  alone,  but  of  metal- 
lic matter  adhering  to  it,  which,  being  enveloped  by  the  film 
of  oxide,  is  prevented  from  coalescing  with  the  fluid  metal 
beneath,  and  is  equally  injurious  in  its  effect  as  if  it  were 
really  extraneous  matter.     Whenever  the  surface  of  filmy 
mercury  is  extended  or  removed,  the  film  from  the  neigh- 
bouring parts  rapidly  expands  over  the  newly  exposed  portion, 
just  as  a  drop  of  oil  extends  and  expands  itself  over  the  sur- 
face of  water.     This  may  be  observed  and  understood  by 
moving  a  card  over  the  surface  of  such  mercury  from  one 
side  to  the  other:  the  film  will  be  collected  on  the  one  side 
of  the  card,  and  the  recent  surface  on  the  other  will  become 
covered  by  an  extension  of  that  which  is  on  the  metal  im- 
mediately in  its  neighbourhood.     If  the  operation   be  re- 
peated, still  the  renewed  surface  will   be  re-covered,  and 
thus  a  large  quantity  of  film  may  be  collected,  which  if  ex- 
amined appears  to  consist  for  the  greater  part  of  metallic 
mercury.     And  though  after  many  operations  of  this  kind 
the  surface  of  the  metal  will  be  much  cleaner  than  at  first, 
yet  exposure  to  the  air  for  a  while,  especially  if  aided  by 
agitation,  will  soon  bring  the  surface  into  its  first  dirty  con- 
dition, and  this  will  continue  so  long  as  the  mercury  con- 
tains metallic  impurities. 

1279.  The  manner  in  which  these  films  interfere  with  ex- 
periments made  over  the  mercurial  trough,  is  principally  by 
preventing  contact  between  the  metal  and  the  jars  or  other 
vessels  used  (789).     If  a  jar  be  dipped  into  the  mercury,  it 
does  not  break  through  the  film  and  come  in  contact  with 
the  pure  metal  beneath,  but  the  film  expands  between  the 
glass  and  the  metal,  and  from  its  comparatively  solid  and 
rigid   nature,  entirely  prevents   that  close  contact  which 


572 

would  occur  between  pure  mercury  and  the  glass.  Or  if 
the  jar  be  laid  with  its  side  upon  the  mercury,  every  particle 
of  the  thick  and  wrinkled  film  that  is  included  between  the 
glass  and  the  metal,  will  retain  its  place  upon  the  sides  of 
the  jar,  whatever  may  be  the  depth  or  position  in  which  it 
may  afterwards  be  placed  under  the  surface  of  the  mercury. 
1280.  When  a  jar  thus  circumstanced  contains  gas,  of 
which  a  portion  is  required  to  be  transferred  into  another 
vessel,  the  consequence  is,  that,  as  soon  as  the  jar  is  so  in- 
clined as  to  cause  the  gas  to  approach  its  edge,  the  latter 
escapes  (788);  for  instead  of  passing  out  in  bubbles,  and 
ascending  through  the  metal  into  the  vessel  above,  it  tends 
to  pass  up  the  side  of  the  jar,  between  the  glass  and  the  film, 
into  the  air.  This  is  the  result  of  want  of  continuity,  or  at 
least  of  close  contact  there  ;  and  though  the  gravity  of  the 
mercury  around  the  gas  passing  from  the  edge  of  a  jar,  is  a 
force  generally  sufficient  to  enable  it  to  overcome  and  break 
through  the  cohesion  of  mercury  when  clean,  and  to  occasion 
it  to  rise  in  distinct  bubbles  through  the  metal,  it  is  not  suffi- 
cient to  do  so  when  the  cohesion  of  the  film  is  added  to  that 
of  the  metal;  and  when,  from  the  interference  of  the  film 
between  the  metal  and  the  glass,  a  passage  upwards,  although 
in  a  somewhat  inclined  position,  is  already  opened  for  it. 

1231.  In  the  same  manner  when  the  beak  of  a  retort  is 
dipped  into  such  mercury  for  the  purpose  of  delivering  the 
gas,  instead  of  passifig  out  in  bubbles,  it  will  frequently 
creep  round  the  edge  of  the  glass  and  ascend  between  the 
neck  and  the  mercury  into  the  air  (789).  This  takes  place 
with  greater  facility  as  the  mercury  is  more  impure  and 
filmy;  as  the  inclination  of  the  beak  approaches  to  the  per- 
pendicular; and  as  the  gas  evolved  tends,  by  its  action  on 
the  metal  or  otherwise,  to  favour  the  formation  of  films. 
Such  gases  as  euchlorine,  muriatic  acid,  ammonia,  &c.,  are 
more  apt  to  do  this  than  oxygen,  hydrogen,  nitrogen,  &c. 

1282.  Small  quantities  of  mercury,  as,  for  instance,  a 
pound  or  two,  may  be  purified  upon  particular  occasions  by 
very  ready  and  simple  processes.  Dr  Priestley's*  method  is 

*  Experiments  and  Observations  on  Air,  Vol.  iv.  Sect,  xvi.;  or  abridged  edition, 
iii.  439. 


MERCURY  PURIFIED BY  NITRATE  OF  MERCURY.  573 

a  most  excellent  one,  and  highly  worthy  of  attention.  So 
much  foul  mercury  is  to  be  put  into  a  ten  or  twelve  ounce 
stoppered  bottle  as  will  occupy  about  a  fourth  part  of  its 
capacity,  the  stopper  to  be  put  in,  the  bottle  inverted,  and 
being  held  in  both  hands  is  to  be  shaken  violently,  the  hand 
that  supports  it  being  generally  struck  against  the  thigh. 
After  twenty  or  thirty  strokes  the  stopper  is  to  be  taken  out, 
and  the  air  in  the  phial  changed  for  fresh  air  by  blowing  into 
it  with  a  pair  of  bellows.  The  mercury  will  soon  become 
black,  and  a  quantity  of  the  upper  part  will  appear  as  if  it 
were  coagulated,  so  as  to  be  easily  separable  from  the  rest; 
the  phial  is  then  to  be  inverted,  and  the  mouth  being  covered 
with  the  finger,  all  the  metal  that  will  flow  easily  is  to  be 
poured  out,  and  the  black  coagulated  part  put  into  a  cup 
by  itself;  by  pressure  with  the  finger  this  may  easily  be  sepa- 
rated into  running  mercury  and  black  powder,  the  former, 
with  the  rest  of  the  metal,  is  then  to  be  returned  to  the  bot- 
tle and  agitated  as  before.  This  process  is  to  be  repeated 
till  no  more  black  matter  separates,  and  it  is  not  a  little 
remarkable  that  the  operator  will  be  at  no  loss  to  know 
when  that  is  the  case,  because  the  whole  of  the  mercury 
becomes  pure  at  once;  and  Dr  Priestley  observes,  with  regard 
to  a  portion  of  mercury  containing  lead  which  had  been 
thus  treated,  that  "  whereas  while  the  lead  was  in  the  mer- 
cury, it  felt,  as  I  may  say,  like  soft  clay,  the  moment  the 
lead  is  separated  from  it,  it  begins  to  rattle  as  it  is  shaken, 
so  that  any  person  in  the  room  may  perceive  when  it  has 
been  agitated  enough."  Mercury  purposely  rendered  im- 
pure by  lead  and  tin  was  found  to  be  perfectly  purified  by 
this  process. 

1283.  Another  method  is,  to  put  the  mercury  to  be  cleaned 
into  a  bottle,  to  add  a  little  nitrate  of  mercury  or  a  small 
quantity  of  diluted  nitric  acid,  to  agitate  well  for  a  minute 
or  two,  then  to  wash  off  the  soluble  parts  with  any  portion 
of  yellow  powder  formed,  and  to  dry  the  mercury  with  a 
cloth.  If  any  difficulty  should  occur  from  the  separation  of 
the  mercury  into  an  infinity  of  globules,  which  may  proceed 
so  far  at  last  as,  with  the  intervening  water,  to  give  the  whole 
a  soft  solid  appearance,  it  is  easily  overcome  by  drying  the 


574          TESTS  OF  THE  PURITY  OF  MERCURY. 

mercury  after  it  is  well  washed,  in  an  evaporating  basin  by 
heat.  As  the  water  evaporates,  the  globules  of  mercury 
will  run  together,  and  the  metal  will  be  obtained  in  its  clean 
and  pure  state. 

After  any  of  these  processes,  the  adhering  dust  should  be 
removed  by  passing  the  metal  through  a  paper  cone  or  fun- 
nel (1272). 

1284.  The  tests  of  the  purity  and  cleanliness  of  mercury 
are,  the  absence  of  all  film  or  powder,  when  a  portion  is 
shaken  quickly  for  a  moment  in  a  clean  tube  or  bottle;  the 
freedom  of  its  motions  upon  the  surface  when  agitated;  the 
extreme  mobility  of  its  globules  when  a  little  is  poured  into 
a  clean  dish  and  broken  into  small  parts;  the  perfect  rotun- 
dity of  form  at  the  receding  edge,  when  a  portion  is  made  to 
flow  from  side  to  side  of  a  glass  dish  or  other  clean  vessel; 
the  largeness  of  the  depression  which  exists,  when  it  is  put 
into  a  dry  bottle,   between  the  sides  of  the  glass  and  the 
metal  at  the  surface  of  the  mercury ;  and  the  ready  pointing 
of  a  small  magnetic  sewing  needle  when  laid  upon  its  sur- 
face out  of  the  magnetic  meridian. 

1285.  When  mercury  has  been  purified  and  cleansed  for 
very  particular  experiments,  as  those  relating  to  the  barome- 
ter and  thermometer,  extreme  care  is  required  that  its  sur- 
face be  not  soiled  by  any  portion  of  dirt  from  the  hands  or 
the  vessels  used.     The  smallest  quantity  of  greasy  matter, 
or  of  deliquescent,  or  animal,  or  vegetable  substances  so- 
luble  in  water,  is  enough  to  render  it  improper  for  these 
uses:  it  is  rapidly  diffused  by  motion  over  the  whole  surface 
of  the  metal,  and  even  a  touch  with  the  finger  is  sufficient  to 
communicate  so  much  impurity  as  to  render  the  mercury  in- 
applicable in  the  construction  of  accurate  instruments. 

1286.  A  glass  should  always  be  appointed   and  kept  in 
one  particular  place  to  receive  any  residual  portions  of  mer- 
cury that  may  be  left  in  an  impure  state  after  experiments, 
or  gathered  from  the  table  in  a  dirty  condition.     They  are 
thus  saved  and  accumulated,  and  when  in  considerable  quan- 
tity may  be  freed  from  mechanical  impurity  by  washing  (348), 
and  then  be  purified  by  that  one  of  the  methods  described 
which  may  be  most  applicable   (1274).     In  this  manner  a 


GENERAL  RULES.  575 

continual  saving  of  metal  is  effected  to  a  great  extent;  the 
quantity  thus  returned  to  the  trough  in  an  active  laboratory 
in  the  course  of  a  year  being  very  considerable. 


SECTION  XXI. 

General  Rules  for  young  Experimenters. 

1287.  BESIDES  the    numerous   directions   which   occur 
throughout  the  preceding  pages,  there  are  certain  general 
precepts  and  rules,  the  observance  of  which  will  be  found  of 
great  service  not  only  to  those  who  are  commencing  the  prac- 
tice of  experimental  inquiries  in  chemistry,  but  likewise  to 
such  as,  having  made  some  progress,  have  indulged  them- 
selves in  irregular  habits.     They  all  relate  to  method,  that 
great  source  of  facility  and  readiness  which  is  equally  influ- 
ential in  the  performance  of  the  most  common  and  the  most 
difficult  processes. .   Such  as  are  given  in  this  section  have 
been  proved   by  long  trial :  it  is  not  supposed  that  they  in- 
clude all  that  are  advantageous,  but  they  are  all  that  suggest 
themselves  to  the  mind  of  the  author  as  worthy  to  be  classed 
together  for  their  general  usefulness.     Those  who  may  add 
to  them  will  deserve  the  thanks  of  the  practical  chemist. 

1288.  A  particular  and  convenient  part  of  the  laboratory 
tables  should  be  appointed  for  all  general  operations  of  ex- 
periment.    It  should  be  considered  as  a  place  intended  for 
working  only,  and  should  not  be  encumbered  by  things  care- 
lessly laid  upon  it:  it  should  be  understood  that  every  article 
placed  there  by  the  experimenter  is  sacred  for  the  time ;  that 
no  apparently  dirty  glass  or  useless  bottle  is  to  be  removed, 
nor  any  arrangement  upon  it  disturbed  by  others  who  may 
be  in  the  laboratory,  but  that  all  is  to  be  left  until  the  expe- 
rimenter himself  has  disposed  of  them  or  given  special  direc- 
tions to  that  purport.     It  is  desirable  in  a  long  course  of 
experiments  that  this  place  should  be  cleared  as  much  as 
possible  every  evening,  that  it  may  be  ready  the  next  day  for 


576  GENERAL  RULES NOTE  BOOK. 

further  progress,  but  unless  this  be  done  by  the  experimenter, 
or  under  his  particular  directions,  it  should  be  left  untouched. 

1289.  By  the  side  of  this  portion  of  the  table  should  be 
another,  appointed  to  receive  apparatus,  bottles,  and  other 
articles  that  are  done  with.     The  putting  of  a  thing  here 
should  be  considered  as  a  direction  that  it  may  be  cleansed 
and  restored  to  its  proper  place.     The  experimenter  will  do 
well  to  disembarrass  his  part  of  the  table  during  his  pursuits, 
by  moving  his  dirty  glasses,  waste  precipitates  and  mixtures, 
and  every  thing  for  which  he  has  no  further  present  use,  to 
this  place,  that  they  may  be  taken  away.     It  is  convenient 
that  a  wooden  tray  should  remain  on  the  spot,  which,  when 
filled  with  dismissed  apparatus,  may  be  at  once  removed 
towards  the  sink  and  replaced  by  another. 

1290.  The  laboratory  note-book,  intended  to  receive  the 
account  of  the  results  of  experiments,  should  always  be  at 
hand,  as  should  also  pen  and  ink.     All  the  results  worthy  of 
record  should  be  entered  at  the  time  the  experiments  are 
made,  whilst  the  things  themselves  are  under  the  eye,  and 
can  be  re-examined  if  doubt  or  difficulty  arise.     The  prac- 
tice of  delaying  to  note,  until  the  end  of  a  train  of  experi- 
ments, or  to  the  conclusion  of  the  day,  is  a  bad  one,  as  it 
then  becomes  difficult  accurately  to  remember  the  success- 
ion of  events.     There  is  a  probability  also  that  some  impor- 
tant point  which  may  suggest  itself  during  the  writing, 
cannot  then  be  ascertained  by  reference  to  experiment,  be- 
cause of  its  occurrence  to  the  mind  at  too  late  a  period. 

1291.  The  account  of  the  day's  experiments  should  always 
be  prefaced  by  noting  down  in  the  book  the  day,  month, 
and  year  ;  and  if  the  experiments  relate  to  gaseous  manipula- 
tion, the  height  of  the  barometer,  and  the  temperature  of  the 
laboratory. 

1292.  On  commencing  the  examination  of  a  substance  of 
unknown  nature,  the  experimenter  should  first  proceed  to 
the  most  general  and  instructive  experiments,  and  then  to 
those  which  are  more  particular.     He  should  therefore  apply 
heat  to  the  substance   contained   in  a  tube,  and  remark 
whether  it  fuse  or  volatilize;  he  should  then  heat  it  in  the 
air  upon  platinum  foil,  observing  whether  it  will  burn  or  not, 


GENERAL  RULES.  577 

whether  it  will  evolve  fumes,  &c.  Afterwards  it  should  be 
heated  in  water  in  a  tube,  and  observed  whether  it  be  solu- 
ble; and  then  trials  should  be  made  to  ascertain  if  it  be  sapid, 
if  it  be  soluble  in  alcohol,  &c.  These  general  examinations 
will  soon  indicate  to  what  class  of  bodies  the  substance  be- 
longs, and  will  point  out  the  particular  train  of  investigation 
it  may  require;  after  which,  the  substance  may  be  dissolved 
by  acids  or  alkalies,  or  any  other  proper  solvent,  and  its 
properties  more  minutely  ascertained. 

1293.  When  a  substance  has  been  brought  into  solution, 
and  its  relation  to  various  tests  and  re-agents  is  to  be  con- 
sidered, it  will  be  proper  to  proceed  methodically  in  examin- 
ing the  different  substances  eliminated  by  their  action,  and 
not  to  wander  from  one  to  another.     The  examination  of  the 
first  product  or  educt  should  be  completed  before  proceed- 
ing to  that  of  a  second,  unless  indeed  it  be  expected  that  a 
particular  trial  of  one  will  throw  light  upon  the  nature  of 
another.     Generally  speaking,  it  is  best  to  pursue  the  pre- 
cipitates, reserving  the  remaining  solution  until  these  are 
examined.     Thus,  if  an  ore  be  dissolved  in  an  acid,  and  the 
solution  be  precipitated  by  potassa,  the  precipitate  should 
in  this  method  be  examined  before  the  remaining  solution. 
If  this  precipitate  require  solution  in  an  acid,  and  precipita- 
tion by  peculiar  tests,  the  first  precipitate  it  affords  should 
be  examined  and  decided  upon,  and  then  the  solution  con- 
taining the  remainder  resumed,  and  its  nature  made  out. 
This  done,  and  consequently  the  whole  of  the  original  pre- 
cipitate dismissed,  the  solution  which  remained  when  it  was 
thrown  down  by  the  potassa  is  to  be  resumed,  and  treated 
with  other  agents.     Perhaps  carbonate  of  ammonia  may  be 
applied,  and  cause  a  second  precipitate  from  it,  which  is,  as 
before,  to  be  examined  previously  to  the  solution  yielding  it. 

1294.  On  other  occasions,  the  solutions  may  be  investi- 
gated before  the  precipitates.     This  plan,  indeed,  may  be 
followed  generally,  and  possesses  the  advantage  of  supplying 
the  experimenter  with  occupation  in  the  solution,  whilst  his 
precipitates  are  washing.    The  rule  intended  to  be  impressed 
is,  that  the  one  or  the  other  of  these  plans  should  be  adopted 
as  a  constant  practice;  a  deviation  from  which  is  to  be  re- 

3X 


578  GENERAL  RULES. 

sorted  to  only  when  it  is  considered   as  offering  peculiar 
advantages. 

1295.  A  plan  of  this  kind  renders  the  notes  of  the  expe- 
riments also  more  methodical.     The  different  solutions  and 
precipitates  may  be  referred  to  by  letters,  as  is  usual  in  de- 
scribing analytical  process.     Thus,  in  the  instance  quoted, 
the  original  solution  may  be  called  a;  the  precipitate  by 
potassa,  6;  the  remaining  solution,  c;  the  solution  of  the 
precipitate,  d;  the  precipitate  from  it,  e;  and  the  solution 
with  the  rest  of  the  precipitate,  6,  /.     The  solution  c  being 
then  resumed,  the  precipitate  by  carbonate  of  ammonia  will 
be  g,  and  the  solution  remaining,  h. 

1296.  When  the  substance  to  be  examined  is  small  in 
quantity  and  rare,  those  experiments  must  be  first  made  that 
will  not  prevent  the  performance  of  others.     The  action  of 
heat,  of  water,  and  of  alcohol,  upon  a  substance  may  be 
observed,  and  still  leave  it  in  a  proper  state  for  other  expe- 
riments, as  those  of  solution  and  precipitation.     The  same 
portion  of  water  which  has  been  tested  for  sulphuric  acid 
by  nitrate  of  baryta,  may,  after  filtration,  be  tested  for  mu- 
riatic acid  by  nitrate  of  silver;  whereas  if  muriate  of  baryta 
had  been  used  in  the  first  place,  the  second  trial  would  have 
been  impossible. 

12^7.  New,  important,  and  uncertain  or  unexpected  re- 
sults, are  to  be  repeated  once  or  twice,  that  no  doubt  may 
exist,  at  a  future  period,  as  to  the  accuracy  of  the  notes 
which  have  been  made  at  the  time  of  observation. 

1298.  Upon  making  a  particular  experiment,  as  of  heating 
a  substance  in  some  peculiar  gas,  or  the  decomposition  of  a 
body  by  voltaic  electricity,  all  the  articles  that  are  likely  to 
be  wanted  should  be  previously  prepared  and  close  at  hand, 
that   no  hesitation    may  occur  in   the  performance  of  the 
experiment,  or  the  attention  be  called  off  from  observing 
the  results,  by  the  necessity  of  supplying  some  important 
omission. 

1299.  When  a  long  series  of  experiments  with  the  spirit- 
lamp  is  in  progress,  a  candle  or  lamp  continually  burning 
should  be  at  hand. 

1300.  On  examining  a  mineral  water  by  precipitants,  the 


GENERAL  RULES.  579 

glasses  used  should  be  placed  in  a  row,  each  before  the  pre- 
cipitant which  has  been  added  to  the  water  it  contains:  and 
they  should  remain  for  half  an  hour,  that  any  ulterior  indi- 
cation of  the  test  may  not  be  overlooked,  yet  without  risk  of 
mistaking  one  glass  for  another. 

1301.  Every  substance  or  glass  that  is  entirely  done  with, 
should  be  dismissed,  and  placed  at  once  on  the  tray  of  dirty 
articles  (1289). 

1302.  Besides  the  working-place  (1288),  another  uncon- 
nected with  the  busy  part  of  the  laboratory  should  be  ap- 
pointed, from  which  nothing  is  to  be  moved  without  the  ex- 
perimenter's direction.     There  are  many  occasions  on  which 
experiments  or  solutions  are  to  be  placed  aside  for  a  week 
or  two,  to  be  again  resumed.     These  should  be  labelled, 
and  put  into  a  place  which,  from  previous  appointment,  is 
considered  as  containing  nothing  that  may  be  disturbed. 
In  this  way  the  experimenter  will  often  avoid  the  disagree- 
able circumstance  of  finding  that  what  he  intended  to  re- 
serve for  future  examination  has  been  dismissed  to  the  sink 
or  the  dust-hole.     A  third  place  of  this  kind  may  be  ap- 
pointed in  a  cupboard,  out  of  the  way,  for  the  reception  of 
experiments  that  require  weeks  or  months  for  their  perform- 
ance (14),  or  for  things  that  cannot  be  resumed  before  long 
periods  have  elapsed. 

1303.  All  products,  educts,  precipitates,  or  solutions,  that 
are  set  aside  for  some  time,  should  be  labelled  (1345, 1363), 
and  referred  to  by  their  names  or  marks  in  the  note-book. 
Thus  the  precipitates  and  solutions,  before  spoken  of  (1295), 
should  have  labels,  a,  6,  c,  &c.,  on  the  glasses  or  bottles 
containing  them.     When  the  products  are  new  and  impor- 
tant, this  should  be  done  immediately,  that  no  possibility  of 
mistake  from  delay  may  be  allowed  to  occur.     The  use  of 
gummed  or  pasted  paper  (1118,  1345)  removes  all  trouble 
from  this  operation. 

1304.  Finally,  the  general  rules  for  cleanliness  and  order, 
so  often  inculcated,  are  to  be  attended  to.     This  Section 
cannot  be  better  closed  than  by  the  very  excellent  observa- 
tions of  Macquer  on  this  subject.     He  says,  "  A  persuasion 
must  exist  that  arrangement,  order,  and  cleanliness  are  essen- 


580  GENERAL  RULES. 

tially  necessary  in  a  chemical  laboratory.  Every  vessel  and 
utensil  ought  be  well  cleansed  as  often  as  it  is  used,  and  put 
again  into  its  place :  labels  ought  to  be  attached  to  all  the 
substances,  mixtures,  and  products  of  operations  which  are 
preserved  in  bottles  or  otherwise;  these  should  be  examined 
and  cleansed  from  time  to  time,  and  the  labels  renewed 
when  required.  These  cares,  although  they  seem  to  be 
trifling,  are  notwithstanding  the  most  fatiguing  and  tedious, 
but  the  most  important  and  often  the  least  observed.  When 
a  person  is  keenly  engaged,  experiments  succeed  each  other 
quickly:  some  seem  nearly  to  decide  the  matter,  and  others 
suggest  new  ideas ;  he  cannot  but  proceed  to  them  imme- 
diately, and  he  is  led  from  one  to  another;  he  thinks  he 
shall  easily  know  again  the  products  of  his  first  experiments, 
and  therefore  he  does  not  take  time  to  put  them  in  order; 
he  prosecutes  with  eagerness  the  experiments  which  he  has 
last  thought  of,  and  in  the  mean  time  the  vessels  employed, 
the  glasses  and  bottles  filled,  so  accumulate,  that  he  cannot 
any  longer  distinguish  them,  or  at  least  he  is  uncertain  con- 
cerning many  of  his  former  products.  This  evil  is  increased, 
if  a  new  series  of  operations  succeed,  and  occupy  all  the  labo- 
ratory ;  or  if  he  be  obliged  to  quit  the  place  for  some  time, 
every  thing  then  goes  into  confusion.  Hence  it  frequently 
happens  that  he  loses  the  fruits  of  much  labour,  and  that  he 
must  throw  away  almost  all  the  products  of  his  experiments. 
"The  only  method  of  avoiding  these  inconveniences  is  to 
employ  the  cares  and  attentions  above  mentioned.  It  is, 
indeed,  unpleasant  and  very  difficult  continually  to  stop  in 
the  midst  of  the  most  interesting  researches,  and  to  employ 
valuable  time  in  cleaning  and  arranging  vessels  and  attach- 
ing labels.  These  employments  are  capable  of  cooling  and 
retarding  the  progress  of  genius,  and  are  tedious  and  dis- 
gusting ;  but  they  are,  nevertheless,  necessary.  Those  per- 
sons whose  fortunes  enable  them  to  have  an  assistant  opera- 
tor, on  whose  accuracy  and  intelligence  they  can  depend, 
avoid  many  of  these  disagreeable  circumstances;  but  they 
ought,  nevertheless,  to  attend  to  the  execution  of  these 
things.  We  cannot  depend  too  much  on  ourselves  in  these 
matters,  however  minute,  on  account  of  their  consequences. 


USES  OF  EQUIVALENTS WOLLASTON5S  SCALE.  581 

This  becomes  even  indispensable  when  the  experiments  are 
to  be  kept  secret,  at  least  for  a  time,  which  is  very  common 
and  often  necessary  in  chemistry. 

"  When  new  researches  and  inquiries  are  made,  the  mix- 
tures, results,  and  products  of  all  the  operations  ought  to  be 
kept  a  long  time  well  ticketed  and  noted  (1363,  1364).  It 
frequently  happens  that  at  the  end  of  some  time  these  things 
present  very  singular  phenomena,  which  would  never  have 
been  suspected.  There  are  many  beautiful  discoveries  in 
chemistry  which  were  made  in  this  manner,  and  certainly  a 
much  greater  number  which  have  been  lost  because  the  pro- 
ducts have  been  thrown  away  too  hastily,  or  because  they 
could  not  be  recognised  after  the  changes  which  happened 
to  them.* 


SECTION  XXII. 

USES  OF  EQUIVALENTS— WOLLASTON'S  SCALE. 

1305.  THERE  is  a  small  instrument,  the  invention  of  Dr 
Wollaston,  which  though  not  directly  concerned  in  the  actual 
performance  of  chemical  operation,  is  of  great  and  constant 
use  in  the  laboratory,  either  in  supplying  the  information 
requisite  previous  to  an  experiment,  or  afterwards,  in  inter- 
preting arid  extending  its  results  :  it  would  therefore  be  im- 
proper to  pass  it  by  unnoticed,  in  a  work  the  very  object  of 
which  is  to  point  out  to  the  inexperienced  those  practices 
and  contrivances  which  facilitate  the  acquisition  of  experi- 
mental evidence.  The  instrument  is  called  a  Synoptic  Scale 
of  Chemical  Equivalents,  or  more  usually  fVollaston's  Scale. 
The  paper,  by  its  author,  describing  the  nature  of  the  scale, 
and  the  manner  of  ascertaining  the  numbers  appropriated  to 
the  different  substances  upon  it,  is  inserted  in  the  Philoso- 
phical Transactions  for  1814.  The  scale  itself,  as  purchased 

*  Dictionnaire  de  Chimie,  par  Macquer,  ii.  486. 


582  DEFINITE  NATURE  OF  COMPOUNDS. 

of  the  instrument-maker,  consists  of  a  movable  slider  with 
a  series  of  numbers  upon  it,  from  10  to  320,  on  each  side  of 
which  and  on  the  fixed  part  of  the  scale,  are  set  down  the 
names  of  various  chemical  substances. 

1306.  It  is  not  the  object  of  this  volume  to  teach  the  prin- 
ciples of  chemistry,  and  they  are  at  no  time  entered  into  fur- 
ther than  is  necessary  to  make  the  student  acquainted  with 
so  much  of  the  nature  of  the  matter  spoken  of  as  is  necessary 
for  a  clear  comprehension.     It  will  be  sufficient  therefore  to 
state  that  the  scale  is  founded  on  three  important  points, — 
the  constancy  of  composition  in  chemical  compounds;  the 
equivalent  power  of  the  quantities  that  enter  into  combina- 
tion, and  the  properties  of  a  logometric  scale  of  numbers ; 
and  to  explain  briefly  how  these  contribute  to  the  formation 
of  the  instrument. 

1307.  The  same  compound  body  is  always  of  the  same 
composition ;  no  variation  in  the  proportion  of  its  elements 
can  by  any  possibility  take  place.     48  parts  of  potassa  com- 
bine with  54  parts  of  nitric  acid  to  produce  102  parts  of 
nitre ;  no  method  of  putting  the  substances  together,  as  by 
causing  an  excess  of  the  one  or  the  other,  or  abstracting  one 
from  a  previous  state  of  combination,  or  allowing  other  sub- 
stances to  be  present,  can  cause  any  change  in  these  pro- 
portions.    Nor  is  this  confined  to  the  numbers  48,  54,  and 
102;  but  whatever  may  be  the  quantity  of  these  elements  in 
combination,  or  of  the  nitre  produced,  the  proportions  will 
be  the  same. 

1308.  Hence  the  composition  of  a  substance  being  once 
accurately  ascertained,  it  requires  no  further  investigation ; 
for  whenever  that  substance  re-occurs,  whatever  may  be  its 
quantity,  the  proportions  of  the  elements  existing  in  it  may 
be  deduced  from  the  former  determination ;  and  whether 
nitre  be  produced  by  combining  together  pure  nitric  acid 
and  potassa,  or  by  using  nitric  acid  with  carbonate  of  pot- 
assa, or  precipitating  a  nitrate  of  copper  by  potassa,  or  in 
any  other  manner,  still  it  will  contain  the  above  proportions 
of  potassa  and  nitric  acid :  whatever  its  quantity,  yet  •£/•% 
parts  of  it  will  be  potassa,  and  T5^  nitric  acid.     It  is  but 
another  form  of  this  natural  law  to  say  that  the  same  quantity 


EQUIVALENT  PROPORTIONS.  583 

of  an  element  always  requires  the  same  quantity  of  another 
element  to  form  the  same  resulting  compound. 

1309.  The  second  point,  or  the  equivalent  power  of  the 
quantities  which  enter  into  combination,  is  not  so  evident  as 
the  former;   but  it  is  abundantly  confirmed  by  experiment. 
If  a  quantity  of  sulphate  of  soda  in  solution  be  poured  into 
a  solution  of  nitrate  of  baryta,  the  latter  being  in  excess,  a 
quantity  of  sulphate  of  baryta  will  precipitate,  and  nitrate 
of  soda  will  remain  in  solution  with  the  excess  of  nitrate  of 
baryta.     So  much  of  the  nitrate  of  baryta  will  be  decom- 
posed as  is  sufficient  to  supply  the  necessary  quantity  of 
baryta  to  combine  with  the  whole  of  the  sulphuric  acid  in 
the  sulphate  of  soda,  and  to  form  sulphate  of  baryta  with  it; 
but  the  point  now  particularly  to  be  observed  is,  that  the 
quantity  of  nitric  acid  which  leaves  the  baryta  will  be  ex- 
actly that  required  to  combine  with  the  soda  separated  from 
the  sulphate  of  soda,  to  form  with  it  the  neutral  salt,  nitrate 
of  soda;  for  the  two  solutions,  after  mixture  and  chemical 
change,  will  be  found  as  neutral  as  before. 

1310.  It  is  evident  from  the  result  of  this  experiment,  that 
the  nitric  acid  is  exactly  equivalent  in  combining  and  satu- 
rating power  to  the  sulphuric   acid ;  for  they  have  both 
equally  neutralized  the  portion  of  soda  in  the  solution,  and, 
what  is  more,  they  have  also  both  equally  neutralized  the 
portion  of  baryta,  which  has  changed  acids  during  the  ex- 
periment.    Upon  very  slight  consideration  it  will  be  per- 
ceived too,  that  the  baryta  in  the  sulphate,  and  the  whole 
of  the  soda,  are  similarly  circumstanced  with  respect  to  each 
other ;  for  they  have  both,  during  the  experiment,  exactly 
neutralized  the  active  portions  of  the  two  acids.     The  excess 
of  nitrate  of  baryta  undergoes  no  change  during  the  experi- 
ment, and  is  merely  considered  as  present  to  insure  the  total 
decomposition  of  the  sulphate  of  soda.     If  the  quantity  of 
dry  nitrate  of  baryta  has  been  132  parts,  and  the  quantity 
of  dry  sulphate  of  soda  72,  then  the  whole  of  the  acids  and 
bases  present  will   have  changed  places  in  the  manner  just 
described. 

1311.  Similar  phenomena  are  presented  by  all  other  neu- 
tral saline  bodies:  the  reciprocity  of  saturating   power  is 


584  CHEMICAL  EQUIVALENT. 

found  to  exist  as  above  described  whenever  chemical  change 
takes  place,  and  is  therefore  dependent  upon  no  particular 
body,  but  belongs  to  all.  Hence  a  correct  notion  may  be 
formed  of  the  meaning  of  the  term  equivalent  as  applied  to 
bodies  acting  chemically.  The  quantities  of  substances, 
which,  by  combining  together,  saturate  each  other,  are 
equivalent  in  their  power  of  combination  ;  thus  40  parts  of 
sulphuric  acid  are  equivalent  to  the  saturation  of  78  parts 
of  baryta.  The  quantities  of  two  or  more  substances  which 
combine  with  and  saturate  an  equal  quantity  of  the  same 
substance,  are  equivalent  to  each  other  in  their  saturating 
power;  thus  40  parts  of  sulphuric  acid  and  54  parts  of  nitric 
acid  are  equivalents,  for  both  are  competent  to  combine 
with  and  neutralize  32  parts  of  soda  or  78  parts  of  baryta 
(1310);  and  the  latter  are  equivalents  for  the  same  reason. 
,  Also  the  quantities  of  compound  bodies  which  naturally  act 
upon  each  other  are  equivalents,  because  the  same  propor- 
tional quantities  are  always  necessary  and  always  sufficient. 
1312.  The  term  chemical  equivalent  may  therefore  be 
used  to  imply  that  proportion  of  a  body  which  is  necessary 
to  act  upon  another  body,  the  circumstances  of  chemical 
affinity  being  such  as  to  permit  action  to  take  place;  and  it 
has  been  found  that  the  proportions  are  the  same  for  one 
body,  whatever  other  body  it  be  compared  with.  So  that  if 
a  particular  number  be  arbitrarily  taken  to  represent  the 
quantity  of  any  one  substance  competent  to  enter  into  com- 
bination, and  be  called  its  equivalent,  then  all  the  equivalents 
of  other  substances  may  be  set  down  in  numbers,  those  num- 
bers being  in  the  same  proportion  to  the  first  number,  that 
the  combining  quantities  of  the  bodies  they  represent  are, 
to  the  combining  quantity  of  the  substance  to  which  that 
first  number  belongs.  Thus  in  the  change  between  nitrate 
of  baryta  and  sulphate  of  soda  (1309),  suppose  the  number 
40  to  be  assumed  as  the  equivalent  number  of  the  sulphuric 
acid  present,  then  32  will  be  the  equivalent  of  the  soda,  for 
so  much  is  combined  with  the  40  of  sulphuric  acid;  and  54 
will  be  the  equivalent  of  the  nitric  acid,  for  so  much  will 
combine  with  the  32  of  soda,  and  78  will  be  the  equivalent  of 
the  baryta;  118  will  be  the  equivalent  of  the  sulphate  of 


LOGOMETRIC  LINE  OF  NUMBERS.  585 

baryta,  72  of  the  sulphate  of  soda,  132  of  the  nitrate  of  ba- 
ryta, and  86  of  the  nitrate  of  soda. 

1313.  The  determination  of  these  equivalents,  or  equiva- 
lent numbers,  is  purely  a  matter  of  experiment.     Any  errors 
which  we  may  adopt  with  regard  to  their  value,  depend  en- 
tirely upon  the  errors  of  our  experiments,  or  our  mistaken 
interpretation  of  them,  and  not  upon  a  possible  change  of 
their  real  value,  under  any  circumstances.     So  that  once 
well  ascertained,  they  become  a  safe  and  invaluable  source 
of  information  to  the  chemist ;  which  he  may  refer  to  and 
use  with  the  utmost  facility,  by  means  of  Dr  Wollaston's 
scale. 

1314.  The  third  point  necessary  to  the  scale  is  the  logo- 
metric  line  of  numbers;  or,  as  it  is  termed,  the  common 
Gunter's  line  of  numbers.     It  will  be  found  that  the  numbers 
are  so  arranged  in  this, line,  that  at  equal  intervals  they  bear 
the  same  proportion  to  each  other.     The  student  will  easily 
observe  and  understand  this,  by  measuring  a  few  distances 
upon  the  scale  with  a  pair  of  compasses,  or  even  a  piece  of 
paper.     If  his  paper  extend  from  10  to  20,  it  will  also  extend 
from  20  to  40,  or  from  55  to  110,  or  from  160  to  320.  What- 
ever number  is  at  the  upper  edge  of  the  paper  will  be  dou- 
bled at  the  lower.     If  any  other  distance  be  taken,  the  same 
effect  will  be  observed.     If,  for  instance,  the  paper  extends 
from  10  to  14,  then  any  other  two  numbers  found  at  its  upper 
and  lower  edge  will  be  in  the  same  proportion  as  these  two 
numbers  10  and  14.     Thus  make  the  upper  number  100,  and 
the  lower  number  will  be  140. 

1315.  Now,  supposing  that  the  paper  were  cut  of  such  a 
width  that,  one  of  its  edges  being  applied  upon  the  scale  to 
the  number  representing  the  equivalent  of  one  body,  the 
other  should  coincide  with  the  number  of  the  equivalent  of 
a  second  body;  then  upon  moving  the  paper,  wherever  it  was 
placed  over  the  numbers,  those  at  its  upper  and  lower  edges 
would  still  represent  the  corresponding  proportional  quanti- 
ties of  the  two  bodies  as  accurately  as  at  first,  because  the 
numbers  at  equal  distances  on  the  scale,  are  proportional  to 
each  other.     Thus,  suppose  the  upper  edge  were  made  to 
coincide  with  40,  and  the  lower  with  78,  then  the  upper  edge 

3Y 


586  SCALE  OF  EQUIVALENTS HOW  CONSTRUCTED. 

might  be  called  sulphuric  acid,  and  the  lower  baryta;  and 
this  width  once  ascertained,  the  paper  wherever  applied  upon 
the  scale,  would  show  at  its  lower  edge  the  quantity  of  baryta 
necessary  to  combine  with  the  quantity  of  sulphuric  acid 
indicated  by  its  upper  edge. 

1316.  It  is  evidently  of  no  consequence  whether  the  paper 
be  moved  up  and  down  over  the  scale,  or  the  line  of  num- 
bers be  moved  higher  and  lower,  to  bring  its  different  parts 
to  the  edges  of  the  paper.     And  supposing  the  piece  of  paper 
just  described  to  be  pasted  upon  the  side  of  the  scale,  then 
by  moving  the  latter  any  of  the  numbers  might  be  made  to 
coincide  with  the  upper  or  lower  edge  at  pleasure,  and  con- 
sequently the  quantity  of  sulphuric  acid  necessary  to  com- 
bine with  any  quantity  of  baryta,  and  vice  versa,  ascertained 
by  mere  adjustment  and  inspection  of  the  scale.  Or  if,  instead 
of  referring  to  the  separate  piece  of  paper,  marks  were  to  be 
made  on  the  side  of  the  scale  at  40  and  78,  and  named  sul- 
phuric acid  and  baryta,  the  same  object  would  be  attained, 
and  the  same  method  of  inquiry  rendered  available. 

1317.  Other  substances  are  to  be  put  down  in  the  scale 
exactly  in  the  same  manner.     Thus  the  scale  being  adjusted 
until  the  number  40  coincides  with  the  sulphuric  acid  already 
marked,  then  sulphate  of  baryta  is  to  be  written  at  118,  and 
thus  its  place  is  ascertained;  nitrate  of  baryta  at  132;  soda 
at  32 ;  sulphate  of  soda  at  72;  and  a  similar  process  is  to  be 
adopted  with  every  substance,  the  number  of  which  has  been 
ascertained  by  experiment.     The  instrument,  which,  in  this 
state,  merely  represents  the  actual  number  supplied  by  ex- 
periment, will  faithfully  preserve  the  proportions  thus  set 
down,  whatever  the  variation  of  the  position  of  the  slider 
may  be.     It  is  therefore  competent  to  change  all  the  nume- 
rical expressions  to  any  degree  required,  the  knowledge  of 
one  only  being  sufficient  first  by  adjustment,  and  then  by 
inspection  to  lead  to  the  rest. 

1318.  A  few  illustrations  of  the  powers  and  uses  of  this 
scale  will  be  sufficient  to  make  the  student  perfect  master 
of  its  nature  and  applications.     Suppose  that  in  analysing  a 
mineral  water,  the  sulphates  in  a  pint  of  it  have  been  decom- 
posed by  the  addition  of  muriate  of  baryta,  and  the  resulting 


SCALE  OF  EQUIVALENTS ITS  USE.  587 

sulphate  of  baryta  washed,  dried,  and  weighed:  from  its 
quantity  may  be  deduced  the  exact  quantity  of  sulphuric  acid 
previously  existing  in  the  mineral  water.  Thus,  if  the  sul- 
phate of  baryta  amount  to  43.4  grains,  the  slider  is  to  be 
moved  until  that  number  is  opposite  to  sulphate  of  baryta, 
and  then  at  sulphuric  acid  will  be  found  the  quantity  re- 
quired, namely  14.7  grains.  In  the  same  manner  the  scale 
will  give  information  of  the  quantity  of  any  substance  con- 
tained in  a  given  weight  of  any  of  its  compounds;  these 
having  previously  been  deduced  from  experiment,  and  accu- 
rately set  down  on  the  scale  in  the  manner  just  explained 
(1317,  1307). 

1319.  If  it  be  desired  to  know  how  much  of  one  substance 
must  be  used  in  an  experiment  to  act  upon  another,  it  is  evi- 
dent that  the  equivalent  must  be  taken,  and  this  may  be 
learned  from  the  scale.     Suppose  that  a  pound  of  sulphate 
of  baryta  has  been  mixed  with  charcoal,  and  well  heated,  to 
convert  it  into  a  sulphuret,  and  that  by  the  addition  of  nitric 
acid  it  is  to  be  converted  into  nitrate  of  baryta.     The  quan- 
tity of  acid  which  will  probably  be  required  may  be  learned 
by  bringing  100  to  sulphate  of  baryta,  and  then  by  looking 
for  the  number  opposite  nitric  acid  :  it  will  be  found  to  be 
46.     But  this  represents  the  quantity  of  dry  acid ;  casting 
the  eye  therefore  lower  down  upon  liquid  nitric  acid  of  a 
specific  gravity  of  1.50,  it  will  be  found  that  61  Ibs.  or  a  little 
more  is  the  equivalent  for  100  Ibs.,  and  consequently  that 
61  hundredth  parts,  or  somewhat  above  six-tenths  of  a  pound 
of  such  acid  will  be  sufficient  for  the  pound  of  sulphate  of 
baryta  operated  with. 

1320.  If  a  certain  weight  of  carbonate  of  baryta  be  re- 
quired in  that  moist  and  finely  divided  state  in  which  it  is  ob- 
tained by  precipitation,  and  in  which  it  cannot  be  weighed, 
the  accuracy  of  the  quantity  may  be  insured  by  taking  the 
equivalent  of  dry  muriate,  or  nitrate  of  baryta,  precipitating 
it  by  an  excess  of  carbonate  of  potassa,  and  then  washing  off 
the  salts  which  remain  in  solution.     Suppose  100  grains  of 
the  carbonate  were  required;  by  bringing  that  number  to 
carbonate  of  baryta,  it  will  be  found  that  the  quantity  of  dry 
muriate  necessary  will  be   105.8  parts,  and  the  quantity  of 


588         ILLUSTRATION  OF  THE  USE  OF  SCALE. 

nitrate  133.4 ;  and  if  the  quantity  of  carbonate  of  potassa 
necessary  for  this  purpose  be  also  required,  it  will  be  found 
opposite  the  name  of  that  substance  on  the  scale,  to  be  little 
less  than  70  parts,  so  that  5  or  10  parts  more  will  insure  a 
satisfactory  excess. 

1321.  The  second  paragraph  of  Dr  Wollaston's  descrip- 
tion of  this  scale  may  be  transcribed  as  a  further  illustration 
of  the  powers  of  the  instrument.     "  If,  for  instance,  the  salt 
under  examination  be  the  common  blue  vitriol,  or  crystallized 
sulphate  of  copper,  the  first  obvious  questions  are — (1)  How 
much  sulphuric  acid  does  it  contain?     (2)  How  much  oxide 
of  copper?  (3)  How  much  water?  He  [the  analytic  chemist] 
may  not  be  satisfied  with  these  first  steps  in  the  analysis, 
but  may  desire  to  know  further  the  quantities  (4)  of  sulphur, 
(5)  of  copper,  (6)  of  oxygen,  (7)  of  hydrogen.     As  means  of 
gaining  this  information,  he  naturally  considers  the  quantity 
of  various  re-agents  that  may  be  employed  for  discovering 
the  quantity  of  sulphuric  acid   (8),  how  much  barytes  (9), 
carbonate  of  barytes,  or  (10)  nitrate  of  barytes,  would  be 
requisite  for  this  purpose  ?  (1 1)  How  much  lead  is  to  be  used 
in  the  form  of  (12)  nitrate  of  lead;  and  when  the  precipitate 
of  (13)  sulphate  of  barytes,  or  (14)  sulphate  of  lead  is  ob- 
tained, it  will  be  necessary  that  he  should  also  know  the 
proportion  which  either  of  them  contains  of  dry  sulphuric 
acid.     He  may  also  endeavour  to  ascertain  the  same  point  by 
means  of  (15)  the  quantity  of  pure  potash,  or  (16)  of  car- 
bonate of  potash  requisite  for  the  precipitation  of  the  copper. 
He  might  also  use  (17)  zinc,  or  (18)  iron,  for  the  same  pur- 
pose, and  he  may  wish  to  know  the  quantities  of  (19)  sul- 
phate of  zinc,  or  (20)  sulphate  of  iron,  that  will  then  remain 
in  the  solution." 

1322.  All  these  questions  and  points  are  answered  by 
moving  the  slider  until  the  number  expressing  the  quantity 
operated  with  coincides  with  sulphate  of  copper  crystallized. 
5,  Water.     Let  it  for  instance  be  100:  this  being  brought 
opposite  crystallized  sulphate  of  copper,  the  information  re- 
lative to  all  the  above  points,  except  the  sixth  and  seventh, 
is  supplied  by  mere  inspection.     The  sixth  may  be  supplied 
by  subtracting  (5)  the  quantity  of  copper  from  (2)  the  quan- 


USE  OP  SCALE.  589 

tity  of  oxide  of  copper,  or  by  halving  the  quantity  at  2  oxy- 
gen, or  taking  the  third  of  that  at  3  oxygen.  The  seventh 
relates  to  the  quantity  of  hydrogen  in  the  5  water  present  in 
the  salt;  this  quantity  of  hydrogen  does  not  come  within  the 
line  of  numbers,  but  may  easily  be  obtained  by  doubling  the 
quantity  of  water,  or  doubling  the  quantity  of  the  salt  used, 
which  will  then  bring  10  hydrogen  into  the  scale,  and  the 
half  of  this  is  to  be  taken  as  the  quantity  in  5  water  or  in 
100  grains  of  the  salt.  Putting  therefore  300  to  sulphate  of 
copper,  10  hydrogen  is  indicated  as  17  parts  nearly,  when 
of  course  the  half  of  this,  or  8.5  parts,  is  the  quantity  in  100 
grains  of  the  crystallized  salt  of  copper. 

1323.  Whenever  it  thus  happens  that  the  number  known 
or  the  number  sought  for  is  out  of  the  scale,  then  some  con- 
venient multiplier  of  the  numbers  may  be  used.     The  most 
convenient  method  is  to  use  the  tens  or  the  hundreds  as  units, 
or,  what  is  the  same  thing,  to  consider  for  the  time  that  de- 
cimal points  are  inserted  between  the  units*  and  the  tens,  or 
between  the  tens  and  the  hundreds  of  all  the  numbers  on  the 
scale.     Thus  if  it  were  required  to  ascertain  how  much  mag- 
nesia and  sulphuric  acid  were  contained  in  a  pound  of  crys- 
tallized sulphate  of  magnesia,  no  1  exists  upon  the  scale,  and 
of  course  no  fractions  or  small  parts  of  1 ;  but  imagine  deci- 
mal points  between  the  tens  and  the  hundreds,  then  ten  upon 
the  scale  become  one-tenth,  22  twenty-two  hundredths,  100 
one,  220  two  and  two-tenths,  and  so  on.     Bringing  therefore 
100  to  crystallized  sulphate  of  magnesia,  it  represents  the  1 
pound,  and  by  inspection  it  will  be  found  that  it  contains  16 
hundredths  of  a  pound  of  magnesia,  and  32i  hundredths  of 
a  pound  of  sulphuric  acid. 

1324.  As  another  illustration:  suppose  that  the  quantity  of 
magnesia  in  50  Ibs.  of  crystallized  Epsom  salt  were  required ; 
upon  bringing  50  opposite  the  name  of  the  salt,  the  quantity 
of  magnesia  will  be  found  smaller  than  any  quantity  ex- 
pres&d  upon  the  scale  :  but  all  that  is  necessary  to  obtain 
the  answer  is  to  double  the  quantity  of  the  salt,  and  then  to 
halve  the  quantity  of  magnesia  indicated ;  in  which  way  it 
will  be  found  that  the  50  Ibs.  contain  about  8  Ibs.  of  the 
earth. 


590  SYNOPTIC  SCALE. 

1325.  These  Synoptic  scales  are  generally  constructed  of 
paper  or  wood.  Those  on  paper  are  first  laid  down  accurately 
upon  copper,  are  then  engraved,  impressions  worked  off  upon 
paper,  and  these  impressions  pasted  upon  a  wooden  frame  and 
sjider  prepared  for  them.     It  is  almost  impossible  that  these 
scales  should  be  accurate,  because  of  the  extension  and  con- 
traction of  paper  when  it  is  clamped,  and  again  dried,  and 
the  facility  with  which  it  yields  to  mechanical  impressions, 
and  may  be  stretched  when  in  a  moistened  state.     When 
the  paper  is  pasted  to  make  it  adhere,  to  the  wood,  it  extends 
considerably  in  all  directions;  and  though  this  extension,  as 
caused  merely  by  dampness,  would  not  very  much  surpass 
that  which  had  taken  place  in  the  paper  when  damped,  pre- 
vious to  its  receiving  the  ink  from  the  copper  plate,'  it  is 
seriously  increased  by  the  rubbing  and  other  mechanical 
action  employed,  both  in  applying  the  paste  from  a  brush, 
and  in  afterwards  bringing  the  paper  into  close  contact  at 
every  part  with  the  wood.     These  scales  should  never  there- 
fore be  considered  as  accurate  when  they  first  come  from 
the  instrument-maker.     They  may  be  examined  by  a  pair  of 
compasses  or  a  piece  of  paper,  as  before  described  (1314), 
to  ascertain  how  nearly  equal  intervals  on  the  scale  of  num- 
bers accord  with  equal  proportions  between  the  numbers  at 
the  extremities  of  those  intervals,  and  thus  the  degree  of 
error  in  them,  and  the  part  where  it  exists  to  the  greatest 
extent,  may  be  observed:  but  it  will  be  useless  to  do  so  with 
the  view  of  finding  one  so  accurate  as  to  dispense  with  cal- 
culation in  exact  analytical  experiments. 

Those  scales  which  are  laid  down  directly  upon  wood, 
though  not  liable  to  the  same  sources  of  error  as  the  paper 
scales,  are  still  seldom,  if  ever,  so  accurate  as  to  compete 
with  calculation. 

1326.  The  errors  just  referred  to  relate  to  the  accuracy 
of  the  scale  of  numbers,  and  its  proportioned  value  in  every 
part.     Others  relate  to  the  imperfect  and  inaccurate  results 
of  the  experiments,  by  which  the  numbers  representing  the 
equivalent  or  combining  quantities  of  bodies  are  obtained. 
If  an  inaccurate  result  be  mistaken  for  a  correct  one,  and 
the  proportional  number  of  a  body  be  entered  erroneously 


ERRORS  OF  SCALES  OF  EQUIVALENTS.  591 

upon  the  scale,  it  is  evident  that  all  estimations  of  substances 
including  that  body,  which  are  given  by  the  scale,  must  in- 
volve this  original  inaccuracy.  Whenever  therefore  a  more 
accurate  determination  of  the  number  of  a  body  is  obtained 
than  was  before  possessed,  its  place  on  the  scale  should  be 
corrected;  and  as  the  equivalent  numbers  of  substances,  pre- 
viously undetermined,  are  satisfactorily  ascertained,  they 
should  be  put  upon  the  scale  in  their  proper  situations,  as 
before  described  (1316,  &c.). 

1327.  In  consequence  of  the  unavoidable  errors  in  the 
scale  of  numbers,  which,  however  small,  still  interfere  in  the 
investigation  of  complicated  cases  and  the  determination  of 
accurate  conclusions,  the  instrument  should  onjy  be  used  in 
those  instances  where  accuracy  within  a  certain  degree  is 
sufficient  for  the  purpose.     All  nicer  results  should  be  ob- 
tained by  calculation  from  a  table  of  equivalents :  if,  for  in- 
stance, the  quantity  of  sulphuric  acid  in  64.7  grains  of  sul- 
phate of  baryta  were   required  to  two  or  three  places  of 
decimals,  it  would  be  better  to  take  the  equivalent  num- 
bers of  sulphate  of  baryta  and  sulphuric  acid  from  such  a 
table,  and  to  say,  as  the  first  number  is  to  the  second,  so  is 
64.7  to  the  quantity  of  sulphuric  acid  it  contains,  than  to 
work  with  the  scale.     The  present  determination  of  the  sul- 
phate of  baryta  is  118,  and  that  of  sulphuric  acid  40,  hydro- 
gen being  1  or  unity,  and  as  118  is  to  40,  so  is  64.7  to  21. 932 
very  nearly.     It  will  be  impossible  to  ascertain  this  last  num- 
ber accurately  on  an  ordinary  scale,  or  to  observe  how  far  it 
differs  from  22. 

There  are  numerous  tables  of  equivalents  published  in  dif- 
ferent chemical  works.  Whichever  may  be  adopted  should 
be  examined  from  time  to  time,  and  the  numbers  affixed  to. 
bodies  on  it  corrected,  whenever  they  are  more  accurately 
determined. 

1328.  It  has  been  shown  by  Gay  Lussac  and  others,  that 
all  gases  and  all  volatile  substances  when  in  the  state  of  va- 
pour, combine  or  act  chemically  in  volumes,  which  have 
very  simple  relations  to  each  other.     Thus  a  volume  of  hy- 
drogen combines  with  half  a  volume  of  oxygen  to  form  a 
quantity  of  water,  which,  if  raised  into  vapour,  and  corrected 
for  temperature,  &c.,  is  equal  in  bulk  to  the  volume  of  hy-. 


592  EQUIVALENT  VOLUMES TABLE. 

drogen  used.  A  volume  of  hydrogen  combines  with  a  volume 
of  chlorine,  to  form  two  volumes  of  muriatic  acid;  and  with 
a  volume  of  the  vapour  of  iodine  to  form  two  volumes  of  hy- 
driodic  acid.  Three  volumes  of  hydrogen  qombine  with  one 
volume  of  nitrogen  to  form  two  volumes  of  ammonia;  and 
half  a  volume  of  oxygen,  on  combining  with  carbon  to  form 
carbonic  oxide,  becomes  a  whole  volume. 

1329.  Relations  of  this  simple  kind  have  been  found  to 
exist  in  the  case  of  every  volatile  body,  which  has  been  par- 
ticularly examined  in  reference  to  this  point.  These  volumes, 
once  ascertained,  may  be  considered  in  the  relation  of  equi- 
valents, and  their  proportions  are  so  simple,  as  to  be  remem- 
bered without  the  least  difficulty:   it  is  therefore  highly 
advantageous,  in  all  tables  of  chemical  equivalents,  to  place 
small  diagrams  by  the  sides  of  the  substances  and  their  num- 
bers, which  may  represent  the  volumes  of  the  equivalents 
when  brought  into  the  state  of  gas  or  vapour.     For  it  re- 
quires no  great  power  of  discernment  to  perceive  that,  if 
bodies  combine  in  definite  weights  (1307),  and  also  in  sim- 
ple ratios  of  volumes,  these  volumes  so  combining  must  con- 
tain the  weights  previously  found  to  be  definite :  for  whether 
two  substances  which  combine  to  form  a  third  are  observed 
by  weight  or  volume,  still  they  combine  only  in  one  pro- 
portion. 

1330.  So  arranged,  the  table  will  have  an  appearance  of 
the  following  kind: 

Hydrogen    .     .      1  ...  d 

Oxygen   ...      8  .      .     .  nn 

Chlorine  ...    36  ...  Q 

*Iodine  .     .     .  125  .     .     .  d 

Water "...       9  ...  D 

Muriatic  acid  .     37  ...  L_i_J 

*Hydriodic  acid  126  ...  FT"! 

Ammonia     .     .     17  .     .     .  CO  f 

*  The  best  authority  on  the  subject  of  equivalents  makes  the  equivalent  num- 
ber for  iodine  124,  and  of  course  that  for  hydriodic  acid  125.  Our  author  gives 
Prout's  number.  ED. 

f  The  volumes  represented  in  the  cut  should  be  equal,  except  that  of  oxygen, 
which  is  half  as  large  as  the  others.  The  double  volumes  are  twice  as  large  as 
that  of  hydrogen,  &c. — ED. 


MISCELLANEA USES  OF  CORKS.  593 

and  will  be  found  very  useful  when  referred  to  for  gaseous 
or  vaporous  substances.  The  proportions  of  these  volumes 
are  much  more  easily  remembered  than  the  proportions 
of  their  equivalent  numbers;  which,  added  to  the  facility 
with  which  the  bulks  of  gases  or  vapours  are  ascertained, 
may  often  properly  induce  the  chemist  to  dispense  with  the 
determination  of  weights,  and  work  with  volumes  only. 


SECTION  XXIII. 
MISCELLANEA. 

1.  Uses  of  Corks. 

1331.  THE  cork-drawer  (25),  and  some*  of  the  uses  of 
corks,  have  been  already  referred  to,  whilst  speaking  of  the 
facility  of  their  conversion  into  stands  for  vessels  (67),  and 
handles  for  hot  tubes  (918).     Their  cheapness  and  general 
qualities  place  them  in  constant  requisition  in  the  laboratory. 
They  make  excellent  wedges  at  the  joints  of  glass  apparatus, 
or  between  glass  and  other  substances,  yielding  in  conse- 
quence of  their  elasticity  and  softness,  and  adapting  them- 
selves to  the  form  of  the  glass  over  a  considerable  surface. 

1332.  Their  use  as  stoppers  for  bottles  and  jars  is  very 
common.     When  cut  from  good  cork  they  may  be  employed 
even  inclosing  the  apertures  of  pneumatic  apparatus  attach- 
ed to  the  air  pump;  and  notwithstanding  that,  when  so  em- 
ployed, they  are  subjected  to  the  air's  pressure,  they  will 
remain  perfectly  tight  for  an  hour  or  more,  if  their  surface 
has  been  rubbed  over  with  a  little  soft  cement*  (1127). 
They  are  very  convenient  as  stoppers  for  jars,  globes,  and 
other  experimental  apparatus,  because  of  their  ready  admiss- 

*  Very  imperfect  or  porous  corks,  after  being  so  prepared  and  covered  with 
sheet  gum  elastic,  form  very  tight  stoppers.  To  prevent  the  adhesion  of  the 
caoutchouc  to  the  glass,  it  should  be  slightly  greased.— ED. 

3Z 


*•' 
594  USES  OF  CORKS PAPER. 

ion  of  a  sharp  point,  and  other  modes  of  attachment  (835, 
836).  The  wires  of  deflagrating  spoons  may  be  passed 
through  them  (740).  Tubes  for  voltaic  decomposition  may 
be  prepared  by  closing  their  ends  with  a  cork,  through  which 
a  wire  has  been  passed  (1046).  A  fine  wire  passed  through 
a  cork  will  serve  to  give  motion  to  apparatus  within  a  vessel 
closed  by  the  latter,  without  permitting  any  appreciable  por- 
tion of  air  or  gas  to  pass;  and  in  this  manner  wire  and  cork 
may  occasionally  be  made  to  supply  the  place  of  a  sliding 
rod,  passing  through  an  air-tight  stuffing-box.  Sometimes 
corks  may  be  strengthened,  when  used  as  stoppers,  by  pass- 
ing through  them  a  wire  attached  to  a  metallic  button  at  the 
lower  surface,  and  terminated  above  in  a  ring  or  handle, 
somewhat  in  the  manner  of  decanter  corks. 

1333.  Corks  being  very  bad  conductors  of  heat,  are  formed 
into  ready  and  excellent  handles  for  the  support  of  hot  rods 
and  wires,  and  for  the  insulation  of  hot  pipes.     They  serve 
equally  well  for  the  support  of  cold  apparatus;  and  three  or 
four  corks  or  bungs  make  excellent  feet  to  a  vessel  contain- 
ing a  refrigerating  mixture,  which  is  to  be  preserved  in  a  cold 
state  for  as  long  a  time  as  possible.     A  long  cork  makes  a 
ready  and  good  handle  for  the  pole  of  a  powerful  voltaic  bat- 
tery (1044),  and  prevents  the  unpleasant  effects  of  an  acci- 
dental discharge  of  the   battery,  through  the  arms  of  the 
operator. 

1334.  Those  which  are  supplied  for  laboratory  use  should 
be  both  elastic  and  compact.     When  to  be  used  as  wedges 
between  glass,  or  inserted  into  apertures,  they  may  be  soft- 
ened, either  by  pressure  between  the  fingers,  by  rolling  them 
under  a  weighted  board,  or  by  heat. 

2.  Uses  of  Paper. 

1335.  Paper  will  often  supply  the  persevering  chemist  with 
a  substitute  for  numerous  vessels,  when  his  ardour  urges  him 
to  pursue  a  subject  under  circumstances  of  great  deprivation, 
as  regards  his  usual  means.     Good  wove  and  hot-pressed 
writing-paper  is  the  most  desirable,  but  any  that  is  sized 
may  be  made  to  answer  the  same  purposes.     By  folding  the 
edges  of  triangular  or  square  pieces,  little  vessels  may  be 


PAPER WAXED-PAPER-TUBES.  595 

constructed,  which  are  water-tight,  and  in  which  precipita- 
tions may  be  made,  and  the  action  of  re-agents  observed. 
On  such  occasions,  the  water  or  solution  should  not  be  put 
into  the  paper  vessel  until  the  precipitant  is  ready  to  be 
added,  and  the  result  should  be  immediately  observed ;  the 
short  time  which  then  elapses  will  not  be  sufficient  to  com- 
municate any  sensible  impurity  to  the  fluid  from  the  paper. 
Or  if  the  paper  be  such  as  has  been  imbued  with  wax,  a 
much  longer  time  may  be  allowed  before  any  impurity  com- 
municated from  it  to  the  water  need  be  suspected.  Coloured 
precipitates  are  observed  in  such  vessels  with  great  advan- 
tage. Dr  Paris  long  since  pointed  out  this  use  of  paper  as 
applicable  to  the  detection  of  arsenic  by  nitrate  of  silver. 
Even  heat  may  be  applied  to  water  in  paper  vessels ;  and 
though  it  is  not  often  that  the  experimenter  is  likely  to  be 
driven  to  such  extremities  as  to  have  occasion  to  resort  to 
such  resources,  it  is  proper  that  he  should  be  acquainted 
with  them.  A  pint  or  more  of  water  may  be  boiled  with 
perfect  safety  in  a  paper  vessel  made  out  of  half  a  sheet  of 
good  cartridge  paper,  placed  over  a  chemical  lamp  (212). 

1336.  Waxed  paper  may  be  readily  made  by  laying  the 
paper  upon  a  clean  hot  plate  (609),  and  rubbing  it  over  with 
a  piece  of  wax  tied  up  in  muslin  or  cloth. 

1337.  The  use  of  paper  in  forming  tubes  (246,  272,  842, 
976)  has  been  already  referred  to :  the  elasticity  of  writing 
paper  is  such,  that  a  tube  constructed  of  three  or  four  con- 
volutions, being  tied  round  with  thread  or  twine,  and  pre- 
served from  rough  treatment,  may  be  considered  as  tight  at 
low  pressures.     It  is  not  intended  to  say  that  no  gas  will 
pass  out  of  it  in  any  length  of  time,  except  at  the  extremi- 
ties, but  that  the  quantity  is  so  small  that  such  a  tube  may 
be  used  upon  urgent  occasions  for  the  conveyance  of  hot 
air,  carbonic  acid  gas,  or  coal  gas,  or  in  any  other  experi- 
ment on  gases,  where  exact  quantities  are  not  necessary. 
Those  who  have  suddenly  had  occasion  to  collect  gas  from 
natural  or  unanticipated  sources,  such  as  the  blowers  of  coal 
mines,  the  fissures  of  the  earth,  the  flues  of  furnaces,  or 
brewer's  fermenting  vessels,  will  fully  appreciate  the  use  of 
these  and  similarly  rough  but  ready  instruments. 


596  PAPER  TUBES WRAPPERS FUNNELS. 

1338.  When  the  edges  of  the  paper  are  pasted,  the  tight- 
ness is  more  permanently  ensured.     If  the  whole  of  one  side 
of  the  paper  be  pasted  before  it  be  rolled  up,  the  tube  will 
be  still  tighter  and  stronger,  and  being  then  varnished  or 
covered  with  a  coat  of  drying  oil,  will  serve  for  the  convey- 
ance of  steam  and  water,  as  well  as  of  gases.     It  may  be 
strengthened  if  there  be  occasion  by  passing  twine  round  it 
(272).     Waxed  paper  (1336)  also  makes  excellent  tubes  for 
the  conduction  of  fluids,  vapours,  and  gases. 

1339.  When  the  tubes  are  intended  for  the  conveyance 
of  inflammable  gas,  they  may  be  made  of  paper  which  has 
previously  been  washed  with  a  saline  solution  (976),  so  as 
to  render  it  incapable  of  taking  fire  and  burning  with  flame. 
Tubes  which  are  pasted  or  cemented  together,  are  easily 
made  by  folding  them  upon  a  round  ruler  or  wooden  rod,  or 
upon  a  wire,  a  piece  of  loose  paper  having  been  first  put 
upon  the  ruler  or  wire,  to  permit  of  its  ready  removal  when 
the  tube  is  finished. 

1340.  Round  discs  of  thick  writing  or  cartridge  paper,  or 
of  card,  answer  the  purposes  of  glass  plates  (1348,  1222), 
for  covering  glasses  at  common  temperatures,  and  excluding 
impurities. 

1341.  Waxed  paper  is  very  useful  when  bottles  or  tubes 
cannot  be  obtained,  for  wrapping  up  deliquescent  or  change- 
able substances,  so  as  to  preserve  them  from  water  and  air. 
Solid  bodies,  like  crystals,  which  are  to  be  transported  to 
some  distance,  and  would  be  injured  by  being  folded  up  care- 
lessly in  flat  paper,  may  be  secured  occasionally  in  little 
tubes  of  the  same  material,  closed  by  a  cork  at  each  end, 
the  tube  being  tied  round  with  thread  or  twine  upon  the 
cork. 

1342.  Paper  funnels  are  of  continual  service,  especially  if 
made  of  waxed  or  oiled  paper.     They  may  be  formed  either 
by  rolling  the  sheet  into  a  cone,  the  apex  of  the  cone  being 
in  the  middle  of  one  of  the  sides  of  the  paper,  as  in  a  grocer's 
envelope  for  sugar,  or  by  wrapping  up  the  pieces  of  paper  in 
the  manner  of  a  simple  filter  (533),  and  piercing  the  point. 
The  first  kind  are  the  strongest,  if  the  external  fold  be  made 
fast  by  a  little  paste,  or  a  piece  of  soft  cement  (1125),  and 


PAPER  JACKETS — STOPPERS LABELS.          597 

may  be  made  more  or  less  inclined  in  the  side.  Fluids,  even 
acids,  may  be  poured  through  these  funnels,  especially  if  of 
waxed  paper :  they  also  serve  for  filtering  funnels ;  for  con- 
ducting gas  into  jars  and  bottles  ;  for  collecting  the  gas  of 
stagnant  waters ;  and  for  numerous  other  purposes. 

1343.  Similar  cones  of  paper,  but  of  a  larger  size,  are 
useful  for  keeping  hot  or  cold  materials  from  exposure  to 
the  air  (544),  to  retard  their  change  of  temperature.     If  a 
glass  containing  a  frigorific  mixture  be  applied  to  freeze  a 
substance  inclosed  in  a  tube  or  wrapped  up  in  a  foil,  the 
powers  of  the  mixture  would  diminish  much  more  rapidly 
by  the  free  contact  of  the  air  than  by  the  matter  experi- 
mented upon ;  and  in  the  course  of  an  hour  its  low  tempera- 
ture and  consequent  efficacy  would  probably  be  gone.     But 
being  supported  on  two  or  three  corks,  and  covered  over  by 
a  paper  cone,  the  contact  of  air  and  other  substances  is  pre- 
vented, and  the  glass  will  remain  at  a  very  low  temperature 
for  many  hours.     In  the  same  manner  paper  jackets,  or  loose 
sheets  of  paper,  tied  round  apparatus  which  are  to  be  retained 
in  a  hot  (425,  440,  473,  706,  941)  or  a  cold  (457)  state,  are 
very  serviceable  in  preventing  the  diffusion  or  the  reception 
of  heat  by  the  access  of  air.     If  an  attempt  were  made  on 
a  hot  day  to  freeze  the  water  at  one  end  of  a  Wollaston's 
cryophorus  by  applying  a  freezing  mixture  to  the  other,  it 
would  probably  fail,  because  of  the  rapid  transmission  of 
heat  to  the  exposed  ball,  but  if  this  ball  be  wrapped  up 
loosely  in  one  or  two  folds  of  paper,  then  the  experiment 
will  be  sure  to  succeed. 

1344.  Similar  small  cones  of  paper  held  together  and 
finished  by  folding'the  edge  of  the  base  inwards  all  round, 
serve  as  stoppers  to  flasks,  bottles,  tubes,  &c.,  and  are  often 
useful  in  closing  the  apertures  of  vessels,  especially  such  as 
are  used  for  processes  of  sublimation. 

1345.  Paper,  on  one  side  of  which  a  coat  of  gum,  paste, 
or  any  other  cementing  matter  has  been  applied  which  may 
be  brought  into  an  adhesive  state  by  water,  has  been  already 
referred  to  as  supplying  ready  labels  (1118,  1303).    It  is 
equally  useful  for  the  instantaneous  manner  in  which  it  serves 


4 

598     PAPER  STRING — COPPER  WIRE — GLASS  P&ATES. 

to  form  tubes,  funnels,  and  cones,  and  to  join  fractures  tem- 
porarily, or  wheresoever  adhesion  is  suddenly  required. 

Paper  prepared  in  a  similar  way  with  a  mixture  of  1  part 
wax,  and  4  parts  Venice  turpentine,  forms  excellent  extem- 
poraneous labels,  which  adhere  by  the  warmth  of  the  hand, 
may  be  immediately  written  upon,  and  do  not  peel  off. 

1346.  Tough  paper  may  even  be  made  to  answer  the  pur- 
poses of  string.     A  slip  of  whited  brown  paper,  about  two- 
thirds  of  an  inch  in  width,  being  rolled  together  between 
the  fingers  into  the  resemblance  of  twine,  has  considerable 
strength.     Parcels  packed  up  in  this  manner,  have  arrived 
safely  in  this  country  from  China. 

3.  Uses  of  Copper  Wire. 

1347.  Copper  wire,  when  annealed,  is,  on  account  of  its 
flexibility,  the  best  kind  of  wire  that  can  be  ordinarily  used 
in  the  laboratory  for  binding  apparatus  together.     This  ser- 
vice it  has  to  perform  very  frequently.     It  is  also  very  useful 
in  forming  temporary  supports  for  tapers,  tubes,  or  arranged 
apparatus ;  as  also  in  assisting  in  the  formation  of  apparatus 
itself,  especially  such  as  is  intended  for  electro-magnetical 
experiments.     It  is  the  best  kind  of  wire  for  the  poles  and 
connections  of  Voltaic  and  electric  batteries,  not  only  for  its 
flexibility,  but  also  for  its  high  conducting  power  as  respects 
electricity  (1036).     When  old  or  useless,  it  should  be  wrap- 
ped together,  or  cut  into  pieces  of  about  an  inch  in  length, 
and  reserved  for  the  purpose  of  making  nitrous  gas.     Two 
sizes  of  copper  wire  at  least  will  be  required  in  the  labora- 
tory ;  the  one  about  one-twentieth,  and  the  other  one-fifth 
of  an  inch  in  diameter. 

4.  Uses  of  Glass  Plates. 

1348.  The  glass  plates  mentioned  formerly  (379,  563,  575, 
587)  are  made  by  clipping  fragments  of  plate  glass  (1227, 
1228)  into  circular  discs,  from  one  inch  to  three  or  four  in 
diameter,  and  are  applicable  to  numerous  purposes.     Being 
perfectly  plane  on  both  surfaces,  they  are  often  used  to  close 
the  apertures  of  jars  (740),  of  which  the  tops  or  ends  are 


TIN- FOIL — LEAD-LEAF — SHEET-LEAD.  599 

ground,  and  are  frequently  more  convenient  than  basins  for 
the  transference  of  jars  containing  gas,  especially  from  shal- 
low portions  of  fluid  or  in  confined  situations  (754).  They 
serve  as  covers  to  glasses  and  jars;  as  vessels  for  the  evapo- 
ration and  crystallization  of  small  portions  of  fluids  or  solu- 
tions (575),  and  as  insulators  in  electrical  or  electro-chem- 
ical arrangements.  In  the  latter,  drops  of  the  fluids  to  be 
decomposed  should  be  put  upon  them  (1047),  or  the  metallic 
vessel  containing  the  fluid  should  be  placed  on  the  glass 
plate.  They  are  often  very  valuable  in  testing  minute  quan- 
tities; the  smallest  quantity  of  a  re-agent  may  be  added  to  a 
drop  of  a  solution  placed  on  such  a  plate,  and  from  the  trans- 
parency of  the  plate,  and  the  different  positions  in  which  the 
tested  matter  may  be  held,  the  appearances  may  be  observed 
to  the  greatest  advantage. 

5.  Uses  of  Leaf  and  Sheet-Metals. 

1349.  Tin  foil  is  very  useful  in  the  laboratory  as  a  con- 
ductor of  electricity  for  the  purpose  of  establishing  a  metallic 
communication  between   the  different  apparatus  standing 
upon  it,  and  for  the  purpose  of  forming  metallic  linings  and 
coatings  to  those  which,  like  the  Leyden  jar,  require  them. 
It  may  readily  be  cut  with  scissors  or  a  knife,  and  is  easily 
applied  by  means  of  paste  and  rubbing  with  the  hand,  as  in 
the  case  of  pasted  paper.     It  is  highly  useful  upon  certain 
occasions  of  refrigeration,  particularly  when  a  solid  sub- 
stance requires  immersion  in  the  mixture.     The  metal  leaf 
should  be  wrapped  so  closely  round  the  substance  to  be 
frozen,  as  to  prevent  the  penetration  of  the  frigorific  mixture; 
and  being  a  good  conductor  of  heat,  the  circumstances  are 
then  the  most  favourable  for  rapid  and  great  diminution  of 
temperature.     It  is  often  useful  also  when  wrapped  round 
tubes  to  darken  a  certain  point,  or  -to  cool  that  part  more 
rapidly.     It  is  a  very  manageable  leaf  metal,  but  should  not 
be  handled  carelessly,  lest  it  become  full  of  holes,  when  it  is, 
of  course,  no  longer  a  water-tight  wrapper. 

1350.  Lead  leaf  has  similar  uses.     Sheet  lead  is  of  consi- 
derable service  in  supplying  counterpoises  for  the  balance 
(39),  being  readily  cut  by-  a  knife  or  scissors.     It  is  of  service 


600  COPPER  PLATE — ZINC  LEAF PLATINUM  FOIL. 

in  heating  and  cooling  bodies  by  contact;  and  from  the  faci- 
lity with  which  it  yields  under  the  hammer  or  pressure,  may 
easily  be  formed  into,  dishes  or  basins,  when  those  of  metal 
are  necessary  for  particular  purposes ;  or  into  vessels  for 
freezing,  and  into  other  temporary  apparatus,  when  better 
cannot  be  had. 

1351.  Copper  plate  is  of  great  service  as  an  electromotor, 
and,  in  conjunction  with  the  metal  zinc,  is  of  continual  use 
in  Voltaic  electricity.  Slips  of  it  are  required  also  in  the 
laboratory  for  the  precipitation  of  certain  metals.  It  is  soft 
when  annealed,  and  is  then  easily  bent  into  temporary  me- 
tallic vessels.  Copper  foil  has  been  already  referred  to  as 
of  the  greatest  service  when  wrapped  round  glass  tubes  (716), 
both  in  strengthening  and  conducting  the  heat  uniformly 
over  them.  It  is  often  used  in  the  same  manner,  on  a  smaller 
scale,  with  tubes  closed  at  one  end  and  held  by  the  hand. 
Copper  leaf,  as  it  is  usually  called,  is  a  particular  kind  of 
brass,  which,  being  extended  very  greatly,  answers  well  for 
observing,  in  a  general  manner,  the  effect  of  agents  upon  a 
metal  in  a  finely  divided  state. 

1 1352.  Zinc  plate  and  leaf.  Zinc  rendered  malleable,  and 
rolled  out  into  plate  and  leaf,  is  very  useful  in  both  forms. 
Plate  or  sheet  zinc  is  a  very  powerful  electromotor,  and  with 
sheet  copper,  as  above  mentioned,  enters  into  the  construc- 
tion of  Voltaic  apparatus.  A  temporary  instrument  may  be 
formed  in  a  few  minutes  with  these  two  metals  and  a  few 
discs  of  flannel.  Plates  of  sheet  zinc  are  often  required  for 
the  precipitation  of  metals.  The  foil,  being  thinner  than 
the  plate,  answers  for  similar  occasions  when  a  smaller  quan- 
tity of  metal  than  that  in  the  sheet  is  required,  and,  being 
lighter,  has  on  that  account  partial  superiority.  From  its 
thinness,  also,  it  is  highly  advantageous  in  exhibiting  chem- 
ical action,  mechanical  separation  being  carried  in  it  to  a 
considerable  extent.  It  always  comes  from  the  rolling  mills 
covered  with  a  coat  of  oil,  from  which  it  should  be  freed  by 
washing  with  a  little  soap  or  alkali,  before  it  is  used  in  chem- 
ical experiments. 

1353.  Platinum  foil.  Many  of  the  services  of  this  sub- 
stance have  already  been  referred  to  (204,  236,  1038,  1048, 


GALVANIC  PRECIPITATION WINDSOR  BRICKS.  601 

1051).  In  all  experiments  in  which  it  is  used  to  support 
other  substances  at  high  temperatures,  the  fusible  metals,  or 
evert  their  oxides,  sulphurets,  and  other  compounds,  when 
mixed  with  carbonaceous  matters,  should  be  kept  from  con- 
tact with  it;  for  the  metal  alloying  with  the  platinum  forms 
a  fusible  combination,  and  the  foil  is  destroyed  or  rendered 
impure.  It  is  very  useful  as  an  electromotor.  A  piece  of 
zinc  and  a  piece  of  platinum  foil  in  contact,  when  put  into  a 
solution,  will  separate  many  metals  from  it  if  present :  the 
metal  passes  to  the  platinum,  and  may  afterwards  easily  be 
removed.  An  application  of  this  kind,  made  by  Dr  Wollas- 
ton,  has  been  already  referred  to  (523,  1065).  It  is  not  dif- 
ficult, upon  occasions  of  necessity,  so  to  fold  up  a  piece  of 
platinum  foil  as  to  make  a  vessel  of  it  capable  of  retaining 
fluids,  and  in  that  state  it  may  serve  the  purpose  of  a  platinum 
crucible  so  far  as  to  allow  the  performance  of  an  analysis, 
which  could  not  otherwise  have  been  effected. 

6.  Uses  of  Soft  or  Windsor  brick. 

1354.  This  brick  is  easily  cut  by  a  jagged  knife  or  saw 
into  numerous  useful  forms.     It  assists  by  juxtaposition  in 
building  up  small  charcoal  furnaces,  allowing  of  the  forma- 
tion of  apertures  through  the  brick  itself.     It  is  easily  shaped 
into  stoppers  for  furnace  apertures  (161),  or  into  covers, 
plugs,  and  supports  for  crucibles;  or  into  wedges,  to  be  ap- 
plied where  necessary  about  furnaces  or  rigid  apparatus.    Its 
softness,  in  which  it  much  surpasses  ordinary  brick  or  stone, 
is  a  considerable  advantage,  especially  when  it  is  used  in  con- 
tact with  glass.    These  bricks  are  also  very  useful  as  supports 
upon  the  tables  for  hot  apparatus.     Furnaces,  red-hot  cruci- 
bles, or  heated  iron  plates,  may  be  supported  on  them  very 
well  and   steadily,  the  heat  transmitted   through   the  brick 
being  insufficient  to  do  injury  (197).  They  were  first  brought 
into  notice  for  these  uses  I  believe  by  Mr  C.  Aikin. 

7.  Conduction  of  heat. 

1355.  Heat  may  frequently  be  conducted  by  means  of  a 
solid  mass  of  metal,  to  places  into  which  it  could  not  so  conve- 
niently have  been  introduced  by  other  means,  and  the  chem- 

4  A 


602      CONDUCTION  OF  HEAT — FURNACE  GUARDED. 

1st  will  sometimes  find  his  operations  facilitated  by  such  a 
contrivance.  Sir  Everard  Home  wished  to  coagulate  the 
blood  within  an  aneurismal  tumour  without  disturbing  the 
tumour  or  the  neighbouring  parts.  This  he  effected  by 
passing  a  needle  through  the  place,  and  then  heating  it  on 
the  exterior;  the  heat  conducted  to  the  fluid  within  was  suf- 
ficient to  cause  its  coagulation.  A  similar  instance  is  now 
very  common  in  the  structure  of  certain  lamps ;  in  which 
cocoa-nut  oil  in  a  reservoir  is  preserved  in  the  fluid  state  by 
a  metallic  rod,  one  end  of  which  enters  the  oil,  whilst  the 
other  projects  over  a  flame  several  inches  off. 

1356.  In  operations  with  a  tube  and  a 'spirit  lamp,  parti- 
cular parts  of  the  former  may  be  heated  and  cooled  very 
conveniently  by  means  of  the  conducting  power  of  metals. 
The  manner  in  which  uniformity  of  temperature  may  be  in- 
sured at  the  lower  part  of  a  tube  when  heated  in  the  flame, 
by  enveloping  it  in  copper  foil,  has  been  already  described 
(1351).    If  on  the  contrary  it  be  required  to  cool  a  particular 
portion  of  the  upper  part  of  a  tube  or  other  vessel  (102),  for 
the  purpose  of  more  effectually  condensing  the  vapour  at 
that  place,  the  tube  may  be  wrapped  round  with  metal  foil, 
which  is  to  be  placed  in  contact  with  thicker  metal,  as  sheet 
lead,  or  cooled  by  touching  it  with  wetted  paper.     The  en- 
velope of  foil  may  be  moistened  and  cooled,  when,  if  the 
glass  itself  were  similarly  treated,  it  would  immediately  fly 
to  pieces.     A  heated  basin,  which,  with  its  contents,  requires 
to  be  cooled  rapidly,  may  be  placed  in  water,  or  upon  the 
mercury  of  the  pneumatic  trough:  the  heat  will  be  rapidly 
abstracted.     When  the  end  of  a  tube  in  which  a  substance 
has  been  submitted  to  heat  will   ultimately  require  to  be 
broken  for  examination,  it  may  be  cooled  and  broken  at  the 
same  moment,  by  plunging. it  whilst  hot  into  the  mercury  of 
the  trough. 

1357.  Bricks,  tiles,  and  other  bad  conductors,  are  very 
usefully  interposed  at  times  between  the  laboratory  table 
and  hot  crucible  furnaces,  to  prevent  the  passage  of  heat  to 
the  former  in  an  injurious  degree  (197,  388);  and  in  many 
other  situations  a  bad  conductor  is  of  service  in  a  similar 


HEAT REFLECTING RECEIVING RADIATING.  603 

way,  by  retaining  the  heat  within  its  original  or  intended 
limits. 

1358.  A  very  useful  indication  of  the  conducting  power 
possessed  by  different  substances  for  heat,  is  obtained   by 
putting  them  in  contact  with  the  upper  lip,  or  that  part  of 
the  cheek  which  is  near  to  the  mouth.     These  places  are 
highly  sensible  to  changes  of  temperature;  and  as  the  sub- 
stance which  conducts  best  abstracts  the  largest  quantity  of 
heat  in  a  given  time,  it  will  of  course  feel  the  coldest,  i.  e. 
supposing  all  the  substances  are  at  the  same  temperature, 
and  several  degrees  below  the  temperature  of  the  skin.     In 
this  way  many  differences  of  conducting  power  may  be  ob- 
served.    Another  method   is  to  hold  one  end  or  side  of  a 
piece  of  the  substance  between  the  fingers,  and  to  apply  the 
other  to  the  flame;  the  difference  between  wires  of  silver 
and  platinum  is  thus  easily  distinguished,  and  also  that  be- 
tween various  stones,  diamond,  and  glass.     The  substance 
which  best  conducts  heat  will  first  feel  hot  to  the  fingers. 

8.  Uses  of  reflective  and  receptive  powers. 

1359.  Clean   polished  metallic  surfaces  receive  heat  by 
means  of  radiation  (i.  e.  from  a  hot  body  not  in  contact  with 
them,  but  at  a  distance)  with  great  difficulty;  and  if  made 
hot,  it  is  with  equal  difficulty  that  they  throw  off  their  heat 
by  radiation  into  space  or  to  other  bodies.     Hence  if  a  bright 
metallic  vessel  be  placed  before  a  strong  fire,  it  will  receive 
heat  but  slowly ;  or  if  it  be  filled  with  any  hot  substance  and 
set  in  a  cool  place,  it  will  be  a  long  time  before  it  will  be- 
come cold  by  mere  radiation.     On  the  contrary,  if  the  sur- 
face of  the  vessel  be  covered  with  a  thin  coat  of  lamp-black, 
varnish,  paper,  or  any  substance  not  metallic,  its  power  of 
receiving  and  sending  off  radiant  heat  is  greatly  increased. 
Such  a  vessel  will  soon  become  hot  before  a  fire,  or  if  heat- 
ed, will  soon  cool  to  common  temperatures  by  radiation. 
These  are  facts  which  the  student  will  gain  from  the  most 
elementary  treatises  on  chemistry,  and  which  may  frequently 
be  applied  with  facility  to  useful  purposes.    If  a  crucible  fur- 
nace (158)  require  to  be   placed  so  near  the  sides  of  the 
pneumatic  trough,  or  any  other  piece  of  apparatus,  as  to  en- 


604  WRITING  ON  GLASS. 

danger  its  safety  by  the  heat  radiating  from  it,  a  bright  tin 
plate  should  be  interposed,  when  the  wood  work  will  be  per- 
fectly secure  (196).  But  as  metallic  bodies  are  excellent 
conductors  of  heat,  such  a  shield  should  not  be  placed  in 
contact  with  the  hot  furnace;  or  if  it  must  necessarily  bear 
against  and  be  supported  by  it,  a  piece  of  brick,  or  tile,  or 
stony  matter,  should  intervene  (1357). 

1360.  When  it  is  necessary  to  prevent  change  of  tempera- 
ture in  a  very  hot  or  very  cold  substance  for  a  long  time  to- 
gether, it  may  be  placed  with  advantage  in  a  clean  metallic 
vessel,  the  radiation  or  the  reception  of  heat  by  the  surface 
being  thus  prevented.    The  contact  of  air  which  would 
carry  off  or  communicate  heat  by  conduction  is  to  be  retarded 
by  paper  cones  (544,  1343),  or  by  flannel  wrappers.     Clean 
tin  foil  is  often  useful  in  thus  supplying  a  metallic  cover. 
If,  for  instance,  part  of  the  neck  of  a  retort  were  to  be  pre- 
served in  a  hot  state,  in  order  that  the  vapours  may  be  pre- 
vented from  condensing  too  soon,  the  object  would  often  be 
attainable  by  a  wrapper  of  tin  foil,  when  the  application  of 
flannel,  paper,  or  other  means,  might  be  inconvenient  or  in- 
adequate. 

1361.  If  whilst  heating  a  flask  over  a  chemical  lamp  (212, 
386)  the  sides  of  the  vessel  have  become  blackened  by  the 
smokiness  of  the  flame,  the  deposition  should  be  immediately 
removed,  for  otherwise,  by  its  radiating  power,  it  causes  con- 
siderable dispersion  of  the  heat  which  has  been  previously 
communicated  by  the  lamp. 

1362.  On  the  contrary,  when  the  object,  in  place  of  pre- 
serving the  temperature  constant,  is  to  bring  it  rapidly  up  or 
down  to  that  of  the  neighbouring  bodies,  the  vessels  should 
be  covered  with  a  surface  that  will  radiate  or  receive  heat 
with  facility.     On  such  occasions  metallic  vessels,  such  as 
canisters,  tubes,  the  envelopes  of  foil  applied  to  the  necks  of 
retorts,  &c.,  should  be  blackenea  or  closely  coated  with  a 
good  radiator  of -heat. 


9.  Writing  on  Glass. 


y.  rrrmng  on  wass. 

1363.  When,  in  the  progress  of  active  and  earnest  experi- 
mental inquiry,  various  bottles,  jars,  glasses,  &c.,  containing 


INK  FOR  GLASS SMELLING  BY  A  TUBE.  605 

different  products  and  preparations,  require  to  be  marked  or 
labelled  (1304),  it  is  advantageous  that  this  be  done  with  as 
little  interruption  to  the  general  course  of  the  thoughts  and 
occupations  as  possible.  It  is  often  therefore  convenient  to 
write  upon  the  glass  of  the  vessel  with  a  common  pen  and 
ink,  with  the  intention  of  substituting  a  proper  label  after- 
wards. There  is  no  difficulty  in  writing  with  great  distinct- 
ness upon  glass,  provided  it  be  wiped  perfectly  dry,  the  last 
rub  being  given  with  a  clean  part  of  the  cloth,  and  also  with 
a  slow  motion  to  remove  any  electricity  that  may  have  been 
excited  on  the  surface  of  warm  or  very  dry  glass,  by  the  pre- 
vious quick  action.  The  pen  should  contain  plenty  of  ink, 
the  letters  be  large  and  written  quickly,  and  the  pen  held 
nearly  perpendicular  to  the  glass. — Jars  containing  particu- 
lar gases  over  the  pneumatic  trough,  or  bottles  of  gas  re- 
quired for  temporary  purposes,  may  be  sufficiently  distin- 
guished by  such  inscriptions. 

1364.  If  it  be  required  that  the  writing  should  remain  for 
some  time,  and  should  resist  the'  action  of  the  damp  vapours  or 
acid  fumes  that  are  continually  afloat  in  the  laboratory,  it  is 
convenient  to  prepare  an  ink  by  diluting  black  varnish,  such 
as  Brunswick  black,  with  its  bulk  of  oil  of  turpentine,  and 
keeping  the  mixture,  with  a  pen,  .in  a  bottle  for  this  particu- 
lar purpose.     For  certain  stock-bottles,  and  jars  or  bottles  of 
gas  which  are  put  by  in  damp  or  un-aired  places,  this  method . 
of  labelling  surpasses  paper  and  ink.  The  writing  soon  dries, 
and,  though  pale,  is  very  distinct  and  legible.     If,  in  the 
course  of  five  or  ten  minutes,  or  after  any  greater  lapse  of 
time,  a  little  lamp-black  be  rubbed  over  it  with  cotton  or 
tow,  the  writing  immediately  becomes  as  black  as  that  of 
common  ink,  and  then  will  resist  rubbing  or  wiping  with 
either  wet  or  dry  cloths  for  a  long  time. 

10.  Smelling  by  a  Tube. 

1365.  It  is  desirable,  in  certain  experiments,  to  increase 
in  every  possible  way  the  means  of  perceiving  whether  a 
substance  possesses  odour ;  whether,  for  instance,  ammonia, 
when  reduced  to  very  low  temperatures,  affects  the  olfactory 
nerves  or  not.    At  such  times,  a  tube  six  or  seven  inches  long, 


606  ENGRAVING  ON  GLASS  BY 

applied  in  the  following  manner, is  of  great  use.  One  ex- 
tremity is  to  be  put  into  the  vessel  containing  the  substance, 
and  placed  in  contact  with  it;  the  other  extremity  is  to  be 
applied  to  one  of  the  nostrils,  the  other  being  closed,  and 
then  air  is  to  be  inhaled  through  the  tube.  This  air  will 
pass  by  the  substance  before  it  enters  the  nostril,  and  if  it 
affords  any  odour  it  may  then  be  perceived.  In  this  manner 
substances  inclosed  within  vessels,  or  at  the  bottom  of  tubes 
which  are  subjected  to  very  low  temperatures,  may  be  exa- 
mined; but  when  thus  operating,  the  end  of  the  tube  must 
be  allowed  to  become  as  cold  as  the  substance,  before  it  is 
placed  in  contact  with  it. 

1 1 .  Engraving  on  glass. 

1366.  This  is  an  amusing  and  sometimes  a  useful  experi- 
ment, and,  as  involving  also  a  little  serviceable  practical  ma- 
nipulation, is  worthy  of  description.     Suppose  the  object  be 
to  engrave  a  design  on  a  piece  of  flat  glass ;  common  crown 
glass  will  be  found  the  best  fbr  the  purpose,  and  a  pane  of 
this  substance  should  be  procured,  of  such  dimensions  that  a 
circle  may  be  described  upon  it  large  enough  to  include  the 
intended  drawing.     The  glass  is  then  to  be  warmed  over  a 
spirit-lamp,  sand-bath,  or  other  convenient  source  of  heat, 
and  rubbed  with  yellow  bees'-wax ;  this  will  melt,  and  by 
.using  such  a  quantity  of  it  as  will  flow  readily  upon  the  glass 
when  hot,  a  uniform  coat  may  be  applied.     If,  when  cold,  it 
.prove  to  be  not  quite  uniform, 'still  if  every  part  of  the  surface 
to  be  engraved  be  perfectly  covered,  it  will  suffice.    The 
design  is  then  to  be  traced  upon  the  waxed  side  with  a  coarse 
point,  every  mark  being  made  to  penetrate  the  wax.     The 
point  may  be  that  of  a  knife,  or  a  piece  of  wire,  or  a  brad- 
awl ;  if  made  flat  at  the  end  in  one  direction,  but  round  in 
another,  so  as  to  resemble  a  minute  round-edged  chisel,  no 
difficulty  will  be  found  in  making  lines  through  the  wax, 
finer  or  coarser,  according  to  the  relative  position  of  the  edge 
or  end  of  the  tool,  and  the  line  which  it  is  describing.     If  the 
design  be  previously  drawn  upon  paper  with  ink,  it  may 
be  easily  seen  and  traced  through  the  wax. 

1367.  An  eVaporating  basin,  either  of  earthenware  or  me- 


MEANS  OF  HYDROFLUORIC  ACID.  607 

tal  (369,  1350),  is  to  be  selected  of  a  diameter  that  will  in- 
clude the  whole  of  the  design  when  the  glass  plate  is  inverted 
over  its  mouth.     Coarsely-bruised  fluor  spar,  in  quantity 
equal  to  about  two  ounces  for  a  pint  basin,  is  to  be  put  into 
the  basin  with  a  sufficient  quantity  of  strong  oil  of  vitriol  to 
make  it  into  a  thin  paste;  the  two  substances  are  to  be  stir- 
red together  with  a  wire,  and  the  waxed  plate  put  over  the 
mouth  of  the  basin  with  the  design  downwards.     A  very 
moderate  heat  is  then  to  be  applied  to  the  bottom  of  the 
basin,  which  is  best  done  by  means  of  the  sand-bath;  it  soon 
causes  the  evolution  of  fumes  in  abundance  from  the  mixture, 
but  should  never  be  allowed  to  increase  so  as  to  melt  the 
wax  on  any  part  of  the  glass;  a  temperature  of  100°  to  140° 
is  sufficient.     The  basin  and  its  contents,  being  warmed, 
should  be  removed  to  a  co'oler  part  of  the  sand-bath,  and 
left  for  half  an  hour.     The  etching  is  known  to  proceed 
well,  when,  upon  raising  one  edge  of  the  plate,  vapours  are 
visible  within.     At  the  en4  of  the  half  hour,  the  glass  plate 
should  be  rinsed  with  water  to  wash  off  the  adhering  acid, 
and  the  wax  removed  either  by  scraping  it  with  the  edge  of 
a  flat  case-knife,  or  otherwise.     The  design  will  generally 
be  found  perfectly  e-ngraved  upon  the  glass,  and  may  be 
rendered  still  more  evident  by  lightly  rubbing  over  it  a  little 
finely-powdered  vermilion  with  a  ball  of  cotton. 

1368.  If  the  glass  to  be  etched  or  engraved  be  so  formed 
as  not  to  close  the  mouth  of  a  basin  or  capsule,  it  must  be 
waxed  all  over,  which  may  be  done  by  dipping  it  into  the 
melted  substance ;  and  after  the  design  is  drawn  upon  it,  it 
must  be  put  with  the  mixture  of  fluor  spar  and  sulphuric 
acid  into  a  vessel  sufficiently  long  and  deep  to  include  the 
whole  of  the  glass  to  be  etched.  The  mixture  of  fluor  spar 
and  sulphuric  acid  is  to  be  placed  at  the  bottom,  and  the 
glass  supported  over  it  upon  corks  or  wires,  or  suspended 
so  as  to  be -out  of  contact  with  the  mixture.  The  vessel  is 
then  to  be  covered  over,  that  the  vapours  which  arise  may 
be  retained  and  surround  the  glass  on  every  side.  Evapo- 
rating basins,  metallic  dishes,  or  other  metallic  vessels,  not 
having  sufficient  depth,  may  be  made  to  answer  the  purpose 
by  a  paper  cap  or  cone  (1343)  put  over  the  edge  rather 


608  SMALL  AIR-GAUGES. 

tightly :  the  upper  part  of  such  a  cone  serves  the  purpose 
of  a  chamber  for  the  reception  of  the  glass  to  be  engraved, 
and  the  vapours  that  are  to  act  upon  it. 

.12.  Small  Mr- gauges. 

1369.  The  air-gauges  by  which  the  pressure  of  the  vapour 
of  liquefied  gases  (962)  was  measured,  may  be  made  in  the 
following  manner.     Some  capillary  tubes  must  be  drawn 
(1176),  not  of  equal  diameter  throughout,  but  much  smaller 
at  one  extremity  than  the  other.     Their  lengths  may  be 
from  8  to  12  inches ;  each  tube  being  formed  as  it  were  of 
two  or  three  portions,  successively  diminishing  in  size  from 
one  end  to  the  other,  so  that  a  volume  of  mercury  at  the 
narrow  end  shall  occupy  a  length  eight  or  ten  times  greater 
than  at  the  wider  end.     Many  of  these  tubes  being  drawn, 
those  are  to  be  selected  for  further  preparation,  in  which  the 
proportions  of  the  different  parts  are  such  as  to  make  them 
most  advantageously  applicable. 

1370.  The  selected  tubes  should  be  graduated  into  parts 
of  equal  capacity  in  the  following  manner.     The  widest  ex- 
tremity of  the  tube  to  be  graduated,  which  is  open  at  both 
ends,  is  to  be  dipped  into  mercury,  and,  when  a  portion  of 
the  metal  has  entered,  raised  into  a  horizontal   position. 
The  mercury  may  easily  be  brought  to  any  required  part  of 
the  tube  by  inclining  it  one  way  or  the  other,  and  at  the 
same  time  slightly  tapping  the  hand  retaining  it;  either  sur- 
face of  the  included  column  of  metal  may  thus  be  made  to 
coincide  accurately  with  any  given  mark  on  the  glass.     The 
mercury,  being  brought  into  the  narrow  part  of  the  tube, 
will  be  very  much  extended  in  length,  and  so  much  should 
be  allowed  to  run  out  as  to  leave  a  portion  not  more  than 
an  inch  in  extent,  which  is  to  be  reserved  in  the  tube,  and 
considered  as  the  measure  of  each  degree  upon  the  scale  of 
the  gauge  to  be  formed.   Being  moved,  in  the  manner  above 
described  a  little  way  towards  the  wider  part  of  the  tube, 
search  is  to  be  made  for  that  portion  of  the  narrow  part 
which,  being  nearly  of  equal  diameter,  or  rather  of  equal 
capacity  for  an  inch  or  an  inch  and  a  half  in  length,  is  also 
nearest  to  the  wider  part.    This  place  in  the  tube,  if  it  exist. 


SMALL  AIR  GAUGES TUBES  GRADUATED.        609 

will  be  easily  found,  for  the  mercury  will  not  undergo  any 
change  in  length  in  different  parts  of  it.  So  soon  as  a  por- 
tion of  the  narrow  part  of  the  tube  of  the  required  regularity 
has  been  discovered,  the  column  of  mercury  is  to  be  brought 
to  the  middle  of  it,  and  the  tube  marked  with  ink  (1363)  at 
the  places  where  it  coincides  with  the  ends  of  the  cylinder 
of  metal;  thus  the  first  degree  will  be  fixed.  Other  degrees 
must  then  be  marked  off  in  a  direction  towards  the  wider 
part  of  the  tube;  the  column  of  mercury  being  removed  for- 
wards for  each  degree  until  its  posterior  surface  coincides 
with  the  mark  which  has  previously  been  made  at  its  ante- 
rior extremity;  the  latter  in  this  new  situation  will  point  out 
the  place  where  the  mark  for  a  new  degree  is  to  be  made. 

1371.  On  proceeding  from  the  narrow  part  of  the  tube  to 
the  wider,  the  included  portion  of  mercury  will  soon  become 
very  much  shortened,  and  increased  in  diameter.     When  its 
length  is  less  than  one  half  what  it  was  at  first,  it  must  no 
longer  be  used  as  a  measure ;  but,  being  returned  towards 
the  narrow  part  of  the  tube,  may  be  employed  to  mark  off 
equal  spaces  or  degrees  beyond  the  first,  these  degrees  being 
only  for  a  temporary  purpose,  and  extending  to  the  end  of 
the  tube.     This  mercury  is  then  to  be  thrown  out,  and  a 
fresh  portion  taken  in  and  adjusted  in  the  manner  already 
described,  until  it  is  equal  in  bulk  to  two  or  three,  or  even 
four  degrees.     It  is  then  to  be  used  to  divide  the  wider  part 
of  the  gauge-tube,  and  an  account  is  to  be  preserved  of  the 
value  of  these  degrees  on  a  piece  of  paper  marked  with  the 
same  intervals,  and  at  the  same  time  as  the  tube.     The 
paper  scale  is  easily  made,  by  laying  the  gauge-tube  upon 
it,  and  making  lines  coincident  with  the  degrees  upon  the 
gauge. 

1372.  By  this  mode  the  tube  will  be  divided  into  a  number 
of  equal  or  proportionate  parts.     So  much  of  the  mercury 
may  then  be  rejected,  as  to  leave  a  quantity  sufficient  to 
form  a  column  in  the  wide  part  about  one-third  or  one-half 
of  an  inch  in  length.     The  end  of  the  column  towards  the 
narrow  part  of  the  tube,  is  to  be  made  to  coincide  with  one 
of  the  graduations  on  the  wide  part,  so  that  a  certain  number 
of  degrees,  20  or  30.  for  instance,  may  be  included  between 

4B 


610  AIR  GAUGES CLOSED COMPLETED. 

it  and  the  extremity  of  the  first  degree  (1370)  marked  down 
on  the  narrow  part  of  the  tube.  Now,  by  employing  a  small 
spirit-lamp  flame,  it  will  be  easy  to  draw  off  and  seal  the 
narrow  part  of  the  tube  at  the  extreme  end  of  the  first  de- 
gree, or  rather  a  little  further  towards  the  end  than  the  exact 
spot.  This  may  be  done  by  heating  so  small  a  proportion 
of  the  tube,  or  of  the  air  within,  that  it  may  be  considered 
as  an  unimportant  quantity,  when  compared  with  the  whole 
bulk  of  air  in  the  gauge.  Even  this  may  be  in  part  com- 
pensated for,  by  sealing  the  tube  a  little  beyond  the  extremity 
of  the  first  degree,  and,  when  sealed,  applying  the  heat  so 
far  up  the  tube  as  to  fuse  the  glass  together  exactly  to  the 
mark  indicating  the  degree.  Supposing  for  a  moment,  that 
by  this  method  a  little  too  much  air,  as,  for  instance,  a  quan- 
tity equal  to  the  twentieth  part  of  a  degree,  has  been  included, 
it  is  only  a  four  hundredth  or  a  six  hundredth  part  of  the 
whole  of  the  air  in  the  gauge,  which  is  of  no  consequence. 
But  it  is  of  essential  importance  that  the  glass  should  after- 
wards be  made  to  coalesce  to  the  line  of  the  first  degree, 
that  the  scale  may  accurately  commence  from  that  line,  and 
that  the  divisions  reckoned  from  it  may  be  equal. 

1373.  When  the  gauge  has  been  so  far  advanced,  the  glass 
should  generally  be  softened  at  the  distance  of  about  an  inch 
on  the  outside  of  the  little  column  of  mercury,  and  drawn  off 
(1167),,  a  small  hole  only  being  left  at  the  extremity  for  the 
entrance  of  the  air  which  is  to  press  upon  the  mercury. 

1374.  These  gauges  are  to  be  introduced  into  the  tubes 
in  which  the  compression  of  the  gases  is  to  be  effected  (962). 
The  gas  tubes  should  be  formed  of  greater  length  than  for 
cases  of  simple  condensation,-  and  bent  twice  instead  of 
once,  so  as  to  form  three  straight  portions  separated  by  two 
angles,  the  gauge  being  in  one  of  the  long  limbs.     If,  during 
the  lapse  of  time,  the  graduation  of  the  gauge  disappear, 
still  the  paper  scale  being  preserved,  may  be  placed  on  the 
outside  of  the  tube,  and  its  termination  made  to  coincide 
with  the  end  of  the  gauge;  in  which  position  it  will  indicate 
the  compression  with  sufficient  accuracy. 

1375.  The  compression  is  estimated  of  course  in  the  same 
manner  as  by  other  similar  gauges.     If  there  are  at  first 


SCREENS  FOR  THE  FACE  AND  EYES.  611 

thirty  degrees  included  between  the  mercury  and  the  closed 
end  of  the  gauge,  and  in  the  course  of  an  experiment  the 
metal  is  forced  up  to  the  fifteenth  degree,  then  the  pressure 
exerted  is  equal  to  two  atmospheres;  if  it  stands  at  the  third 
degree,  it  is  equal  to  ten  atmospheres;  if  at  the  end  of  one 
degree,  it  is  equal  to  thirty  atmospheres.  In  consequence 
of  the  great  length  of  the  first  degree,  it  is  easy  by  such  a 
gauge  to  read  off  to  above  a  hundred  atmospheres;  Marriotte's 
law,  as  supported  by  the  late  experiments  of  Oersted,  and  the 
French  philosophers,  being  considered  as  correct.  These 
gauges,  however  thin,  are  perfectly  safe,  being  subjected  to 
the  same  pressure  within  and  without;  and  for  that  reason 
no  inaccuracy -resulting  from  unequal  pressure  is  likely 
to  rise. 

1376.  Such  gauges  are  of  similar  use  in  the  repetition  of 
M.  Cagniard  de  la  Tour's  experiments ;  and  in  many  others, 
where  gases  or  vapours  are  subjected  to  pressure,  either  by 
mechanical  or  chemical  means. 

13.  Screens  and  Masks  for  the  eyes  and  face. 

1377.  It  is  worse  than  thoughtless  to  neglect  the  proper 
means  of  preserving  the  eyes,  when  experiments  on  danger- 
ous or  explosive  substances,  as  chloride  of  nitrogen,  or  on 
gases  under  great  pressure  in  glass  vessels,  are  in  progress ; 
and  hence  the  use  and  necessity  of  masks  in  the  laboratory. 
A  very  excellent  mask  for  the  defence  of  the  eyes  and  face, 
may  be  made  of  a  piece  of  wire  gauze,  sufficiently  large  to 
cover  the  visage.     It  may  be  attached  at  the  upper  edge  to 
a  spring  band,  which,  passing  round  the  head,  will  retain  it 
in  its  place.     This  mask  is  flexible,  consequently  not  liable 
to  be  shattered  like  one  of  glass,  and  is  free  from  the  incon- 
venience of  producing  dimness,  which  is  often  occasioned 
by  masks  of  glass,  owing  to  the  condensation  of  moisture 
from  the  breath.     But  it  is  objectionable  for  all  experiments 
which  require  close  observation,  because  of  the  interference 
of  the  wire  gauze  with  perfect  distinctness  of  vision;  and 
as  it  allows  the  passage  of  fluids  through  its  meshes,  it  is 
inefficient  in  explosive  experiments,  made   with  corrosive 


612  EXPLOSION-SAFE SILVERING  GLASS. 

liquids,  as  for  instance,  those  upon  the  chloride  of  nitrogen 
by  acids. 

1378.  An  excellent  mask  may  be  formed  of  a  piece  of 
plate  or  even  crown  glass,  guarded  on  the  side  towards  the 
eyes  with  a  sheet  of  mica,  both  being  bored  at  their  upper 
edges,  and  made  fast  to  a  piece  of  wood  which,  being  curved 
and  attached  to  a  band,  will  admit  of  adaptation  to,  and  sup- 
port from,  the  head.     The  glass,  if  broken  by  an  explosion, 
is  prevented  from  doing  harm  to  the  eyes  or  face  by  the 
mica,  and  the  latter  being  flexible  and  tough,  is  not  likely 
to  be  shattered  to  pieces.     Mica  alone  would  scarcely  an- 
swer the  purpose,  unless  of  such  thickness  as  would  colour 
the  transmitted  light,  when  it  occasions  a  dimness  before 
the  eyes;  for  there  is  not  much  of  this  mineral  found  which, 
being  large  and  thick,  is  yet  so  clear  as  to  allow  the  passage 
of  light  through  it  as  freely  as  through  glass.     Mica  too, 
undefended  by  glass,  would  soon  become  rough  and  dull 
from  scratches  and  slight  injuries.     A  mask  of  glass  and 
mica  need  not  descend  far  below  the  eyes,  for  all  beneath 
the  nostrils  to  the  chin  may  be  defended  by  wire  gauze, 
and  thus  dimness  from  the  moisture  of  the  breath  will  be 
avoided. 

1379.  A  pair  of  spectacles,  with  side  as  well  as  front 
glasses,  afford  sufficient  protection  in  many  experiments; 
the  glasses  should  be  large  and  of  thick  .plate  glass.     The 
spectacles  should  fit  close  to  the  eyerbrows  and  cheek  bones, 
and  the  eyes  being  thus  secured,  the  rest  of  the  face  may 
incur  the  risks  of  the  hands  and  other  parts  of  the  body.* 

14.  Silvering  Glass. 

1 380.  The  advantage  of  being  able  to  silver  a  small  surface 
of  glass  for  experiments  on  light  having  been  experienced, 

•  Dangerously  explosive  experiments  are  very  conveniently  conducted  in  a 
«*  safe"  composed  of  a  cylinder  of  wire-gauze,  attached  to  a  circular  wooden  bot- 
tom, and  surmounted  by  a  gauze  wire  top  moving  on  a  hinge.  At  the  side  also, 
a  gauze  wire  door  is  a  convenient  addition.  In  such  a  "  safe,"  eighteen  inches 
high,  and  fifteen  inches  in  diameter,  the  editor  has,  for  several  years,  exhibited 
the  effects  of  the  most  detonating  preparations,  without  the  occurrence  of  a  single 
unpleasant  accident. — ED. 


SILVERING  GLASS.  613 

it  is  assumed  that  the  student  may  have  occasion  to  perform 
the  same  operation :  and  as  regards  the  manner  in  which  he 
may  coat  one  side  of  a  glass  plate  (1348)  with  a  bright  me- 
tallic surface,  and  thus  convert  it  occasionally  into  a  reflector, 
he  will  find  no  difficulty,  by  proceeding  according  to  the 
following  directions.  Having  prepared  the  glass,  a  piece 
of  clean  smooth  tin  foil  free  from  holes  (1349),  is  to  be  cut 
to  the  same  size,  and  laid  upon  a  couple  of  sheets  of  filtering 
(529)  or  blotting  paper  folded  into  quarters.  A  little  mer- 
cury is  to  be  placed  on  the  foil,  and  rubbed  over  it  with  a 
hare's  foot,  or  with  a  ball  of  cotton  slightly  greased  with 
tallow,  until  the  whole  of  the  upper  surface  of  the  leaf  be 
amalgamated  and  bright.  More  mercury  is  then  to  be  added, 
until  the  quantity  is  such  as  to  float  over  the  tin  foil.  A  piece 
of  clean  writing  paper,  with  smooth  edges,  is  to  be  laid  upon 
the  mercury,  and  then  the  glass  surface,  previously  well 
cleaned,  is  to  be  applied  to  the  paper.  The  paper  is  to  be 
drawn  out  from  between  the  mercury  and  the  glass,  whilst 
a  slight  but  steady  pressure  is  to  be  applied  to  the  latter. 
As  the  paper  recedes,  it  carries  all  air  and  dirt  with  it  from 
between  the  glass  and  the  metal,  which  come  into  perfect 
contact. 

1381.  The  mirror  is  now  made,  and  may  be  used  for  an 
experiment ;  but  there  is  still  much  more  mercury  present 
than  is  required  to  mark  the  definite  and  hard  amalgam  of 
tin  constituting  the  usual  reflecting  surface.     If  it  be  desired 
to  remove  this  excess,  the  newly-formed  mirror  must  be  put 
on  its  edge  for  some  days,  when  the  superabundance  of  fluid 
metal  will  drain  to  the  bottom ;  or  it  may  be  put  under  the 
pressure  of  a  flat  board,  in  a  slightly-inclined  position,  and 
loaded  with  weights. 

1382.  The  mercury  used  for  silvering  should  be  free  from 
other  metals ;  and  such  as  has  been  used  in  the  manner  above 
described  should  be  kept  apart  from  the  rest  of  the  labora- 
tory stock,  because  of  the  tin  it  may  contain,  or,  before  being 
added  to  it,  should  be  purified  by  some  of  the  methods  de- 
scribed (1282,  &c.). 


614  PHOSPHORESCENCE HOW  PRODUCED. 

c**-  •/  "         -  ...  .  f      .  ^   . 

15..  Phosphorescence. 

1383.  There  are  many  substances  which,  when  heated, 
become  more  or  less  luminous ;  but  in  numerous  cases,  the 
light  evolved  is  so  feeble  as  to  require  the  most  favourable 
circumstances  to  render  it  visible.     A  usual  and  very  good 
method  of  producing  the  effect  in  ordinary  cases,  is  to  heat 
a  thick  plate'of  iron  to  a  temperature  at  which  it  is  barely 
visible  in  the  dark,  to  place  it  on  a  brick,  and,  after  carrying 
it  into  a  dark  place,  to  sprinkle  upon  it  the  substances  to  be 
tried.     It  is  better  to  heat  the  iron  more  at  one  part  than 
another,  so  that  when  the  former  is  just  visible,  the  latter, 
being  at  an  inferior  temperature,  is  not  sensible  to  the  sight; 
trials  may  then  be  made  on  both  parts  with  the  same  sub- 
stance.    A  substance  often  emits  so  little  light  as  not  to 
yield  any  appearances  on  the  part  of  the  iron  visibly  hot, 
while  it  is  distinctly  phosphorescent  on  the  other  part,  where 
there  is  no  light  to  blend  with  that  evolved. 

1384.  The  substance  should  not  be  altogether  in  fine  pow- 
der: it  is  better  to  experiment  with. a  mixture  of  coarse  and 
fine  parts.     If  the  fine  powder  or  the  mixture  does  not  seem 
to  become  phosphorescent,  a  few  small  fragments  should  be 
tried,  unmixed  with  smaller  portions.    Their  form  becomes 
faintly  visible,  and  may  be  distinguished  on  the  black  iron, 
when  the  light  of  an  indiscriminate  and  general  sprinkling 
cannot  be  certainly  ascertained.     Occasionally  a  fragment 
is  more  advantageous,  because  of  the  different  temperatures 
of  its  parts  at  different  moments,  a  faint  light  appearing  to 
pass  gradually  over  it  as  its  parts  acquire  the  necessary  tem- 
perature. 

1385.  It  is  usually  better  to  place  the  substance  at  once 
upon  a  hot  body,  from  which  it  may  quickly  receive  the  heat 
it  may  require,  than  upon  platinum  foil  or  in  a  crucible,  and 
to  heat  both  it  and  the  vessel  at  the  same  time.     The  ope- 
ration is  then  slower,  because  of  the  larger  mass  to  be  heated; 
and  the  eye  in  certain  cases  becomes  accustomed,  to  such  a 
degree,  to  the  gradual  change  of  light,  as  not  to  notice  it. 
The  quicker  the  phosphorescence  occurs,  the  more  distinctly 
is  it  recognised.     The  eye  should  not  be  directed  towards 


USES  OF  SOLAR  RADIANT  MATTER.  615 

luminous  or  enlightened  bodies  immediately  previous  to  the 
observation,  but  towards  darkness,  that  it  may  be  rendered 
more  sensible  to  the  impression  of  light. 

1386.  Dr  Brewster,  in  giving  an  account  of  some  experi- 
ments by  which  he  recognised  this  property  in  so  many  bo- 
dies as  to  nearly  quadruple  the  number  previously  known  to 
be  phosphorescent,  says,  "  I  never  reduced  the  body  to  pow- 
der, but  always  placed  a  fragment  of  it  upon  a  thick  mass  of 
hot  iron,  carried  into  a  dark  room.     When  the  phosphores- 
cence was  not  readily  perceived  by  this  method,  I  took  a 
pistol-barrel,  and,  having  shut  up  the  touch-hole,  I  intro- 
duced the  mineral  into  the  breech,  and  placed  the  bottom 
of  the  barrel  in  the  fire.     Before  a  red  heat  was  produced, 
phosphorescence  was  distinctly  seen  by  looking  into  the  bar- 
rel, which  I  sometimes  did  through  a  plate  of  glass,  to  keep 
the  heated  air  from  the  eye,  and  sometimes  through  a  small 
telescope,  adjusted  to  distinct  vision  at  the  bottom  of  the 
barrel.     At  other  times  the  mineral  was  not  introduced  into 
the  barrel  till  it  was  taken  out  of  the  fire,  and  till  the  red 
heat  had  entirely  disappeared."* 

16.  Uses  of  Solar  Radiant  Matter. 

1387.  The  rays  of  the  sun,  when  concentrated  in  a  focus, 
have  not  unfrequently  be.en  used  in  heating  bodies  placed  in 
the  middle  of  glass  vessels,  to  which  heat  could  not  other- 
wise be  communicated.     Thus  the  Florentine  Academicians 
and  Sir  Humphry  Davy  heated  the  diamond  in  oxygen  gas. 

1383.  Their  influence  in  occasioning  chemical  change  in 
a  manner  unlike  that  of  any  other  agent,  is  such  as  to  make 
their  application  in  the  laboratory  highly  important  (6);  and 
it  is  to  be  regretted  that  chemists  generally  are  not  more  in 
the  habit  of  trying  their  powers  over  bodies  which  as  yet 
have  not  been  submitted  to  them.  Chloro-carbonic  acid  is 
always  formed  by  their  means;  so  also  is  one  of  the  hydrio- 
dides  of  carbon;  and  the  chlorides  of  carbon  cannot  be  pro- 
duced in  any  other  way  so  advantageously  as  by  their  assis- 
tance: chlorine  will  decompose  water  when  exposed  to  them, 

*  Edinburgh  Philosophical  Journal,  i.  385. 


620  MAGNETISM. 

which  it  can  scarcely  do  without  their  aid;  and  having  these 
strong  evidences  of  a  peculiar  and  very  effectual  power,  there 
is  no  reason  why  we  should  not  hope  to  find,  that  even  solid 
bodies  exposed  to  solar  light,  when  in  contact  with  gases  and 
vapours,  and  also  with  fluids,  exert  an  action  quite  indepen- 
dent of  the  powers  of  heat,  and  adequate  to  the  production 
of  new  results.* 

,17.  Magnetism. 

1389.  Though  magnetism  may  be  thought  to  form  no  part 
of  chemical  science,  yet,  from  its  extraordinary  .development 
by  electricity,  and  its  equally  extraordinary  residence  in 
some  of  the  metals,  it  cannot  but  press  upon  the  attention  of 
the  chemist.     The  present  notice  will  principally  relate  to 
the  use  of  the  magnetic  needle  as  a  test  of  the  presence  of 
magnetism  in  minerals  or  substances  containing  iron,  or  of  its 
development  by  electro-chemical  arrangements. 

1390.  When  a  magnetic  needle  of  the  ordinary  kind  is 
used,  its  point  of  suspension  should  be  very  fine  and  delicate, 
that  no  serious  retardation  of  its  motion  may  be  occasioned 
by  friction;  and  the  agate,  glass,  or  other  cup  which  supports 
the  needle,  should  be  clean  and  smooth  within.     The  mag- 
netic state  of  the  needle  may  be  judged  of  from  the  freedom 
and  readiness  with  which  it  vibrates  when  driven  from  its 
natural  position.     It  may  be  appreciated  also  by  dipping  the 
points  into  iron  filings:  the  brush  of  filings  sustained  should 
be  considerable,  and  quite  at  the  end  of  the  needle;  no  part 
towards  the  middle  of  the  needle  ought  to  show  attractive 
powers  sufficient  to  lift  up  any  particles  of  the  iron. 

1391.  When  the  needle  is  used  as  a  test  of  the  magnetic 
powers  of  a  body,  as  an  ore  of  iron,  or  other  mineral,  it  should 
be  allowed  to  take  its  state  of  rest,  when  the  body  should  be 
approximated  to  one  side  of  either  extremity  or  pole:  the 
attraction  or  disturbance  of  the  needle  will  indicate  the  mag- 
netic state  of  the  substance,  and  the  magnetism  may  be  con- 

*  By  means  of  a  mirror,  most  of  the  experiments  on  the  chemical  action  of 
light  may  be  made  in  even  the  darkest  corner  of  a  laboratory.  A  mixture  of 
chlorine  and  hydrogen,  as  shown  by  Dr  Hare  in  a  very  neat  experiment,  may  be 
thus  most  safely  and  easily  exploded. — ED. 


MAGNETIC  POWER TESTED  FOR.  617 

sidered  of  a  strength  proportionate  to  the  distance  to  which 
the  substance  attracts  the  needle,  or  that  at  which  it  first 
acts. 

1392.  If  the  magnetism  be  very  weak  its  effects  may  be 
rendered  more  evident  by  the  following  management.     Sup- 
pose the  substance  to  be  a  piece  of  iron  ore  applied  on  the 
right  side  of  the  pole,  and  capable  of  deflecting  the  needle 
only  a  very  small  distance  from  its  original  position  :  if  the 
substance  be  removed  sideways,  and  the  needle  allowed  to 
return,  it  will,  if  freely  suspended,  pass  beyond  its  position  of 
rest  to  a  distance  on  the  left  side,  nearly  equal  to  that  to 
which  it  had  been  deflected  on  the  right  side  of  the  magnetic 
meridian,  and  will  regain  its  state  of  rest  only  after  several 
oscillations.     But,  in  place  of  allowing  it  thus  to  regain  its 
state  of  rest  after  it  has  swung  to  the  left  side,  and  is  in  the 
act  of  returning  to  the  right  by  the  attraction  of  the  earth, 
and  the  mere  momentum  of  its  parts,  the  iron  ore  should  be 
again  brought  near  to  it  on  the  same  side,  to  conjoin  its 
attractive  force  with  the  forces  before  mentioned,  and  thus 
to  draw  it  as  far  as  possible  towards  the  right  side.    The  ore 
is  then  to  be  withdrawn  from  the  needle  as  before,  and  when 
the  latter  has  passed  to  the  left  side,  is  to  be  again  applied 
whilst  it  is  returning  to  the  right;  this  is  to  be  done  repeat- 
edly, the  oscillations  of  the  needle  in  one  direction  being  fa- 
voured by  superadding  the  attractive  powers  of  the  ore  each 
time.     This  will  be  found  very  easy  of  performance  by  an 
alternate  movement  of  the  hand  to  and  from  the  pole  of  the 
needle  on  the  right  side;  the  object  being  to  hold  the  ore  as 
near  to  the  pole  as  possible,  while  the  latter  is  passing  from 
left  to  right,  and  to  remove  it  so  as  to  leave  the  needle  quite 
uninfluenced  by  it,  as  the  same  pole  moves  from  right  to  left. 
In  this  manner  a  new  impulse  is  added  to  the  pole  or  needle 
at  each  oscillation,  the  amplitude  becomes  gradually  in- 
creased, and  deflections,  which  at  first  were  scarcely  visible, 
become  extended  to  a  very  considerable  degree. 

1393.  If  it  be  a  weak  repulsive  power  that  is  thus  to  be 
rendered  evident,  the  substance  tried  must  be  made  to  follow 
the  pole  closely  as  it  recedes,  and  is  to  be  withdrawn  to  a 

4C 


618 

distance  as  it  returns  in  the  oscillation :  but  it  is  better  in 
such  a  case  to  use  the  attractive  force  of  the  substance  on  the 
other  pole;  for  no  mistake  can  arise  as  to  any  tendency  of  the 
substance  to  draw  the  pole,  through  the  mere  motion  of  the 
air,  though  such  a  mistake  might  occur  as  to  repulsion, — the 
effect  supposed  to  be  repulsion  being  nothing  more  than 
motion  communicated  mechanically  through  the  air  by  the 
approximated  body,  driving,  as  it  were,  the  air  and  needle 
before  it. 

1394.  M.  Haiiy  has  instructed  us  that,  under  the  combined 
influence  of  the  earth  and  a  magnetic  bar,  a  needle  may  be 
made  a  much  more  delicate  test  of  the  presence  of  small 
magnetic  attractions,  than  when  under  the  earth's  influence 
alone.     The   power  which  is  required  to  deflect  a  needle 
from  its  natural  position  is  least  when  the  deflection  is  small- 
est, and  greatest  when  the  deflection  is  90°.     It  increases 
therefore  from  0  to  90,  and  then  decreases  again;  but  the 
increase  is  in  a  decreasing  ratio,  and  the  decrease  in  an  in- 
creasing ratio,  so  that  it  requires  a  much  greafer  magnetic 
force  to  move  it  from  0°  to  10°,  than  to  move  it  from  80°  to  90°. 

1395.  To  take  advantage  of  this  circumstance,  the  needle 
is  to  be  allowed  to  acquire  a  state  of  rest  when  under  the 
earth's  influence  only;  then  if  the  south  pole  of  a  bar  magnet 
be  approached  towards  the  south  pole  of  the  needle,  the  bar 
being  in  a  line  with  the  needle,  a  repulsion  will  take  place, 
and  the  needle  will  deviate  until  the  repelling  power  of  the 
bar  and  the  attractive  force  of  the  earth  on  it  are  equal  to 
each  other.     This  may  have  brought  the  needle  to  an  angle 
of  30°  with  the  magnetic  meridian,  but  by  approximating  the 
bar  the  effect  may  be  increased,  and  the  angle  rendered 
greater.     In  this  way  the  distance  of  the  bar  is  to  be  dimi- 
nished, until  the  needle  is  very  nearly  at  right  angles  with 
its  first  direction,  and  will  scarcely  retain  that  position,  but 
on  the  slightest  further  degree  of  motion  pass  through  ano- 
ther quarter  of  a  revolution,  or  even  more.     It  is  thus  placed 
in  the  most  favourable  position  as  a  test  of  magnetism;  for  an 
attractive  power,  many  times  smaller  than  that  which  would 
sensibly  deflect  it,  when  in  the  magnetic  meridian,  will  now 


MAGNETISM  OF  A  BAR.  619 

be  sufficient  to  make  it  pass  through  the  few  remaining  de- 
grees to  90°,  and  then  entirely  invert  its  position.* 

1396.  When  a  bar  of  iron  is  examined  for  magnetism  by 
the  needle,  the  method  is,  to  observe  whether  both  ends 
attract  both  poles  at  all  distances,  or  whether  in  any  case  a 
repulsion  of  either  pole  can  be  observed.     This  repulsion  is 
a  proof  of  magnetism  in  the  bar,  but  in  such  cases  it  is  ne- 
cessary to  hold  the  bar  in  a  horizontal  position,  and  perpendi- 
cular to  the  direction  of  the  needle;  for  in  any  other  position 
a  bar  of  soft  iron,  without  previous  magnetism,  will  seem  to 
be  magnetic  and  to  possess  poles,  solely  in  consequence  of 
its  relative  position  to  the  earth   and  needle.     Whilst  in  a 
plane  perpendicular  to  the  dip  of  the  needle,  it  will  not  show 
this  effect,  but  when  out  of  that  plane  the  end  below  acts  as 
a  north  pole  to  the  needle,  and  the  end  above  as  a  south  pole. 
Although  it  has  just  been  said  that  when  in  such  a  plane  it 
shows  no  effect  of  this  kind,  the  assertion  is  not  strictly  true  ; 
for  such  a  plane  being  considered  as  passing  through  the 
thickness  of  the  bar,  all  that  is  above  will  seem  to  have  the 
one  effect  on  the  needle,  and  all  that  is  below  the  other ; 
but  the  power  is  so  slight  in  a  bar  having  this  position,  as  to 
be  scarcely  perceptible  under  ordinary  circumstances. 

1397.  An  iron  bar  may  also  be  examined  for  magnetism  by 
bringing  it  near  fine  iron  filings;  if  it  have  poles  they  will 
attract  the  filings,  but  the  test  is  not  so  delicate  as  the  nee- 
dle.    Iron  filings  afford  ready  indications  of  the  power  of  bar 
magnets;  the  bulk  of  the  brush  taken  up  being  in  propor- 
tion to  the  attractive  power  of  the  bar. 

1398.  Small  temporary  and  very  delicate  magnetic  needles 
may  be  made  by  magnetising  a  common  sewing  needle,  and 

tThis  phenomenon  may  be  perhaps  more  easily  comprehended  by  reflecting, 
t,  by  the  arrangement,  a  needle  of  some  power  is  brought  into  a  state  of  neu- 
trality as  respects  the  terrestrial  magnetism,  and  is  thus  more  sensibly  acted 
on  by  other  attractive  forces.  If  it  were  possible  to  shut  off  the  terrestrial  attrac- 
tion entirely,  without  impairing  the  magnetic  virtue  of  the  needle,  it  would  then 
become  the  most  perfect  test  of  magnetic  virtue  in  other  substances.  '  But  as  we 
know  of  no  means  of  interrupting  communication  between  a  magnet  and  the 
attractive  powers  of  the  earth,  we  are  able  to  effect  the  more  delicate  magnetic 
observations,  only  byicounterbalancing  these  attractive  powers  under  the  most 
advantageous  circumstances  of  position.— ED, 


620  EXPERIMENTAL  PRACTICES. 

then  either  floating  it  upon  water  on  a  small  piece  of  cork,  or 
suspending  it  by  a  single  fibre  of  silk.  For  this  latter  pur- 
pose a  small  ball  of  soft  cement  (1125)  is  to  be  attached  to 
each  end  of  a  piece  of  the  fibre,  about  a  foot  or  two  in  length. 
One  of  these  being  pressed  against  any  convenient  place 
from  which  the  needle  may  be  suspended,  will  adhere  with  a 
force  quite  sufficient  to  support  the  needle.  The  latter,  hav- 
ing previously  been  magnetised,  is  to  be  pressed  against  the 
other  ball  of  cement,  and  adjusted  until  it  balances  in  a  ho- 
rizontal position.  Being  left  to  itself  it  will  take  its  natural 
position  in  the  magnetic  meridian,  and  during  suspension  will 
be  more  delicate,  and  more  readily  obey  impulses  exerted 
upon  it,  than  a  needle  supported  on  a  point. 

1399.  The  needles  are  easily  magnetised  in  the  usual  way 
by  an  ordinary  magnet.  If  such  be  not  at  hand,  a  steel  bar 
may  be  rendered  powerfully  magnetic,  as  Mr  Scoresby  has 
shown,  by  placing  it  in  the  magnetic  dip,  i.  e.  with  one  end 
pointing  about  24i  degrees  west  of  north,  and  downwards,  so 
as  to  make  an  angle  of  721  degrees  with  the  horizon.  When 
the  bar  is  held  in  this  position,  with  one  end  on  a  large 
kitchen  poker  in  the  same  position,  and  the  other  end  struck 
three  or  four  times  with  a  heavy  hammer,  it  will  become  a 
good  magnet,  and  quite  sufficient  for  the  preparation  of 
small  magnetic  needles. 


SECTION  XXIV. 

A    COURSE    OF   INDUCTIVE   AND  INSTRUCTIVE 
PRACTICES. 

THE  chemical  student  must  not  expect  that,  by  reading 
this  book,  he  will  find  himself  ready  and  expert  in  the  appli- 
cation of  the  various  methods  and  contrivances  which  it  de- 
scribes. No  valuable  experimental  knowledge  can  be  ob- 
tained at  so  cheap  a  rate.  Practice  is  essential  to  that  facility, 
without  which  nothing  dependant  upon  the  hands  can  be 


BALANCE WEIGHING.  621 

done  well.  With  the  view  therefore  of  expediting  the  ac- 
quirement of  the  necessary  habits,  the  present  section  will 
contain  a  number  of  practices,  arranged  either  as  single  ex- 
periments, or  in  sets;  the  performance  of  which,  whilst  it 
will  confer  considerable  experimental  readiness,  will  convey 
instruction  relative  to  numerous  important  points  of  chemical 
science,  and  teach  the  application  and  powers  of  the  contri- 
vances described,  when  they  are  afterwards  to  be  applied  in 
trains  of  new  and  original  research.  All  the  experiments  are 
accompanied  by  references  to  the  previous  paragraphs  of  the 
book,  that  the  information  necessary  for  their  successful  per- 
formance may  be  found  at  the  moment  it  is  wanted:  and 
thus,  at  the  same  time  that  the  instruction  given  directs  the 
practical  manipulation,  it  is  itself  illustrated  and  rendered 
more  forcible  by  the  performance  of  the  experiment. 

II.  Balance,  Weighing,  fyc. 

[1.]  Observe  the  equality  and  readiness  of  oscillation  in 
the  balance  (43)  when  the  scales  are  empty,  and  also  when 
they  are  equally  loaded  with,  first,  a  fourth,  and  then  one 
half  of  what  they  ought  to  carry  (44).  Remark  the  differ- 
ence, if  any,  in  the  time  of  the  oscillation  when  the  pans  are 
empty  and  when  they  are  loaded. 

[2].  Load  the  balance  with  the  full  weight  it  is  intended 
to  carry,  then  observe  whether  it  sets  or  not  (44).  If  it  set, 
diminish  the  weights  in  the  scale,  until  the  charge  with  which 
it  first  begins  to  set  be  ascertained. 

[3.]  Try  the  different  weights  of  the  balance  against  each 
other  (49)  in  various  ways. 

1  [4.]  Examine  the  old  brass  weights  belonging  to  the  ba- 
lance, by  counterpoising  them  with  new  and  accurate  weights 
(49) ;  during  the  trial  put  all  the  weights  to  be  tried  on  one 
side,  and  the  ascertained  weights  on  the  other  (59). 

[5.]  Counterpoise  the  balance  by  weights  equal  to  about 
one  half  of  what  it  should  carry  (33);  and  when  in  equili- 
brium, change  the  weights  from  pan  to  pan,  and  observe 
whether  the  balance  still  remains  equipoised  (48,  59). 

[6.]  Weigh  two  pieces  of  solid  substance  together  (52, 
56),  to  the  hundredth  of  a  grain ;  then  weigh  the  two  sepa- 


m- 

622  BALANCE WEIGHING. 

rately,  and  observe  whether  the  sum  of  their  weights  make 
the  first  weight. 

[7.]  Balance  two  pieces  of  writing  paper  in  the  pans  (61) 
by  as  few  cuts  with  the  scissors  as  possible.  Put  these 
papers  successively  into  the  same  pan;  weigh  300  grains  of 
sand  into  each  (62,  59),  and  then  ascertain  whether  the 
weighed  portions  equipoise  each  other. 

[8.]  Counterpoise  a  piece  of  smooth  writing  paper  (61), 
weigh  50  grains  of  magnesia  on  it  (62);  then  pour  off  the 
magnesia,  and  ascertain  whether  the  portion  which  adheres 
to  the  paper  has  rendered  it  sensibly  heavier.  Do  the  same 
with  a  fine  heavy  powder,  as  carbonate  of  baryta.  In  this 
way  an  idea  of  the  quantity  of  powder  which  will  adhere  to 
paper  may  be  acquired. 

[9.]  Weigh  49.7  grains  of  carbonate  of  lime  in  fine  pow- 
der (61,  62),  weigh  a  second  portion  of  49.7  grains,  then  put 
them  together,  and  try  if  they  weigh  accurately  99. 4  grains; 
if  not,  ascertain  whether  the  rest  of  the  weight  is  on  the 
paper,  or  what  has  occasioned  the  apparent  inconsistency  in 
the  results. 

[10.]  Weigh  a  piece  of  glass  or  metal  of  about  400  or  500 
grains  (52),  cool  it  well  (454,  1349),  then  hold  it  for  a  few 
minutes  in  a  glass  containing  a  little  water  at  the  bottom, 
but  so  as  not  to  touch  the  fluid;  afterwards  ascertain  if  the 
weight  of  the  cold  body  has  been  increased  by  moisture  con- 
densed upon  its  surface. 

[11.]  Counterpoise  a  cold  platinum  crucible  (64),  make 
it  hot,  and  putting  it  into  the  pan  in  that  state,  observe  the 
quantity  by  which  the  weight  appears  to  be  diminished  (58). 

[12.]  Counterpoise  a  tube  supported  on  a  cork  (64,  67), 
then  accurately  weigh  a  hundred  graips  of  water  into  the 
tube  (69),  taking  particular  care  that  none  pass  to  the  out- 
side. 

[13.]  Counterpoise  a  glass  (64),  and  weigh  127  grains  of 
mercury  into  it  (130,  131). 

[14.]  Counterpoise  a  bulb  or  little  flask,  supported  on  a 
cork  ring  (64,  67),  weigh  into  it  1 50  grains  of  strong  sul- 
phuric acid  (69),  adjusting  the  quantity  by  a  rod  (70). 

[15.]  Counterpoise  a  little  evaporating  basin  or  capsule 


WEIGHING MEASURING.  623 

(64),  and  weigh  into  it  130  grains  of  Venice  turpentine  in  a 
cleanly  manner  (70),  adjusting  the  quantity  by  the  tip  of  a 
wire  or  rod. 

[16.]  Counterpoise  a  small  glass  (64),  weigh  300  grains 
of  water  into  it  (69);  fuse  some  chloride  of  calcium  in  an 
earthen  crucible  to  dissipate  all  the  water  (642,  669,  670), 
pour  it  upon  a  cold  metallic  or  stone  surface,  and  as  soon 
as  it  is  solid  break  it  into  pieces  and  introduce  two  or  three 
fragments,  together  exceeding  100  grains  in  weight,  into  the 
water,  before  the  chloride  can  have  increased  in  weight,  by 
absorbing  moisture  from  the  air  (72).  Ascertain  the  increase 
of  weight;  then  stir  up  the  solution  carefully  with  a  glass 
rod  until  it  is  perfectly  uniform  (514),  and  afterwards  remove 
so  much  of  it  (69,  71)  as  to  leave  exactly  100  grains  of  chloride 
of  calcium  behind,  i.  e.  if  110  grains  of  the  compound  have 
been  added,  making  410  grains  of  solution,  remove  an  eleventh 
part  of  it,  by  which  10  grains  of  the  chloride  will  be  with- 
drawn, and  100  grains  left  for  analysis,  or  for  experiments. 

[17.]  Balance  a  green  glass  tube  closed  at  one  extremity 
(64,  66),  weigh  into  it  60  grains  of  crystallized  muriate  of 
baryta  in  a  dry  state  (51),  heat  the  tube  so  as  to  drive  off 
the  water  and  fuse  the  muriate  (707);  when  cold,  re-weigh 
it,  and  ascertain  the  diminution  occasioned  by  the  dissipa- 
tion of  water  (59).  It  should  equal  8.71  grains.  Ascertain 
how  many  proportions  of  water  this  accords  with,  either  by 
the  scale  of  equivalents  (1318),  or  by  calculation  (1327). 

[18.]  Weigh  two  or  three  portions  of  solid  matter  by  a 
Black's  balance  (112),  or  an  unadjusted  instrument,  apply- 
ing the  weights  and  the  substances  on  the  same  side  (59); 
then  compare  the  weights  so  obtained  with  such  as  may  be 
obtained  by  weighing  the  same  portions  of  matter  in  a  good 
balance. 

[19.]  Weigh  a  glass  flask  (65),  or  a  tube  (66),  attaching 
it  by  a  wire  to  the  bottom  of  the  pan. 

[20.]  Take  the  specific  gravity  of  a  smooth  solid  body, 
as  a  piece  of  glass  (81,  85).  Take  also  the  specific  gravity 
of  a  piece  of  solid  matter  in  the  rough  state,  for  example,  a 
fragment  of  zinc  or  antimony  (85). 


624  MANAGEMENT  OF  HEAT. 

[21.]  Ascertain  the  specific  gravity  of  alcohol,  of  ether, 
of  sulphuric  acid,  and  of  water,  by  the  bottle  (92). 

[22.]  Make  a  number  of  small  weights  (116);  ascertain 
their  truth  by  trying  them  against  correct  weights  (49). 

[23.]  Make  a  Black's  balance  (112);  compare  its  results 
with  those  obtained  by  a  good  balance  (59,  &c.). 

[24.]  Take  the  specific  gravity  of  water  and  beer  by  the 
hydrometer  (103),  and  compare  the  results  with  those  ob- 
tained by  the  bottle  and  balance  (93). 

III.  Measures.    Measuring,  fyc. 

[25.]  Measure  out  a  pint  of  water  (120,  121),  avoiding 
the  formation  of  bubbles  near  the  graduation.  Whilst  mea- 
suring out  the  fluid  pour  it  slowly  into  the  vessel,  that  the 
exact  quantity  may  be  observed  and  ascertained  at  once. 

[26.]  Pour  a  quantity  of  water  into  an  ungraduated  glass 
or  jar;  then  measure  it  (120,  121);  afterwards  pour  mercury 
into  the  first  vessel,  to  the  same  height  (121),  and  measure 
it  by  a  graduated  vessel  (118),  to  verify  the  first  result. 

[27.]  Counterpoise  a  graduated  measure  in  the  balance 
(64);  pour  a  certain  measure  of  distilled  water  into  it,  four 
ounces  for  instance  (118),  then  weigh  it  (67),  and  ascertain 
whether  the  weight  is  what  it  ought  to  be,  or  1750  grains,  at 
the  temperature  of  62°  F.  (117).  Remove  the  first  portion 
of  water,  and  measure  in  the  same  quantity  a  second  time 
(120).  See  if  its  weight  be  the  same  as  the  weight  of  the 
first,  or  to  what  extent  it  differs.  It  ought  to  be  the  same ; 
and  the  nearer  the  results  approach  in  weight,  the  more  rea- 
son has  the  operator  to  be  satisfied  with  the  accuracy  of  his 
eye  and  habit  of  measuring. 

[28].  Measure  half  a  cubical  inch  of  mercury  (121,  135), 
and  then  ascertain  its  weight  (126). 

[29.]  Mark  a  line  down  a  glass  tube  (129).  Make  a  mark 
across  it  with  a  file  (132),  beginning  either  at  the  line,  or 
extending  on  both  sides  at  pleasure ;  divide  a  space  about 
an  inch  in  length,  first  into  two,  then  four,  and  then  eight 
equal  parts  by  the  eye  (143);  ascertain  the  accuracy  or  in- 
accuracy of  these  divisions,  by  weighing  mercury  into  them 


MANAGEMENT  OF  HEAT.  625 

(126).  Practise  also  the  division  by  the  eye  into  three,  five 
and  ten  parts. 

[30.]  Graduate  a  tube  into  tenths  of  a  cubical  inch  by 
weighing  water  into  it  (65,  127,  71,  126,  129,  &c.). 

[31.]  Graduate  a  tube  into  hundredths  of  a  cubical  inch 
by  weighing  mercury  into  it  (65,  126,  129,  &c.). 

IV.  Management  of  Heat. 

[32.]  Convert  a  blue  pot  or  large  earthenware  crucible 
into  a  furnace  (157,  &c.).  Then  put  some  chalk  into  an 
earthenware  crucible  (642),  and  by  heating  it  in  this  furnace 
(670),  convert  it  into  quick  lime.  Try  whether  it.  has  be- 
come quick  lime,  for  which  purpose  put  a  small  piece  into 
water,  and  add  muriatic  acid;  no  effervescence  should  occur 
(366). 

[33.]  Heat  some  zinc  in  a  Hessian  crucible  in  the  same 
furnace  (158),  until  it  burn  freely  upon  agitation  and  expo- 
sure to  air. 

[34.]  Boil  some  water  in  a  Florence  flask  (383),  on  the 
furnace  sand-bath  (173);  observe  the  temperature  of  the 
steam  that  passes  off  (279,  286),  and  also  of  the  water. 
Introduce  some  iron-filings  into  the  flask,  and  again  observe 
the  temperature  of  the  steam  and  of  the  water  beneath 
(441)-. 

[35.]  Diffuse  1  oz.  of  starch  through  a  pint  of  cold  water, 
allow  it  to  settle  (549),  pour  off  a  little  of  the  water,  and 
evaporate  it  to  dryness  (591);  observe  if  any  thing  remain; 
then  heat  the  mixture  of  starch  and  water,  (380,  &c.)  and 
observe  the  solution  of  the  starch ;  allow  the  fluid  to  stand 
twelve  hours,  then  decant  a  portion  (550),  and  evaporate  it 
to  dryness  (599)  by  a  bath  of  water  covered  with  oil,  and 
observe  how  much  starch  is  left,  and  in  what  state. 

[36.]  Heat  a  little  starch  in  a  tube  (910,  935)  to  500°  by 
means  of  a  metallic  bath  (264),  allow  it  to  cool,  and  then 
upon  adding  water  it  will  dissolve  without  heat :  on  evapo- 
rating the  solution  in  a  basin  over  a  chemical  lamp  (590, 
212),  the  same  results  as  in  the  former  experiment  will  be 
obtained. 
4D 


626  MANAGEMENT  OF  HEAT. 

[37.]  Evaporate  a  portion  of  the  above  solution  of  starch 
to  dryness  by  a  steam  heat  (271,  274). 

[38.]  .Evaporate  a  quarter  of  a  pint  of  mineral  water  to 
dryness  over  a  chemical  lamp  (592,  212);  add  a  drop  of  water 
to  the  residue,  and  observe  whether  it  be  alkaline  by  tur- 
meric paper  (624).  All  the  deep  well-waters  of  London 
yield  alkaline  matter. 

[39.]  Heat  a  piece  of  wood  on  platinum  foil  (1353,  204) 
by  the  spirit-lamp  (199);  observe  the  odour,  the  production 
of  flame,  the  carbonaceous  residue,  and  its  combustion  by  a 
continuance  of  the  heat.  Heat  also  a  piece  of  isinglass  or 
cheese  in  the  same  manner ;  remark  the  fetid  ammoniacal 
smell,  the  flame,  the  fusion,  the  difference  between  its  coal 
and  the  former,  and  the  greater  difficulty  of  incineration. 

[40.]  Fuse  a  mixture  of  equal  parts  of  the  carbonates  of 
potash  and  soda  in  a  platinum  crucible  (653)  by  the  heat  of 
a  spirit-lamp  and  jacket  (206,  666,  667),  afterwards,  if  poss- 
ible, fuse  some  common  salt  in  the  same  manner. 

[41.]  Attain  the  highest  possible  ignition  of  a  platinum 
wire  by  a  spirit-lamp  or  candle  (199,230)  and  the  mouth 
blow-pipe  (216).  Try  the  same  experiment  with  platinum 
foil  (204),  holding  the  foil  vertically,  or  directing  the  flame 
from  below  upwards,  or  from  above  downwards  (231,  233) 
upon  the  metal ;  observe  the  circumstances  of  the  most  in- 
tense heat  (235). 

[42.]  Endeavour  to  fuse  the  extremities  of  a  film  of  asbes- 
tus  by  the  mouth  blow-pipe  and  a  candle  (216,  230,  232). 

[43.]  Melt  first  20  and  then  30  grains  of  bi-carbonate  of 
soda  in  a  platinum  foil  crucible  (1353),  until  they  fuse  freely, 
and  become  fluid  dry  carbonate  of  soda,  using  the  mouth 
blow-pipe  and  spirit-lamp  for  the  purpese  (233).  If  this 
be  found  too  difficult  at  first,  use  a  mixture  of  two  parts 
bi-carbonate  of  soda,  and  one  part  bi-carbonate  of  potassa. 

[44.]  Melt  a  globule  of  tin  on  charcoal  (232)  by  the  mouth 
blow-pipe  and  a  candle  (227,  230),  keeping  it  perfectly  me- 
tallic and  bright  for  one  or  two  minutes  together. 

[45.]  Heat  a  globule  of  antimony  on  charcoal  (240)  by 
the  mouth  blow-pipe  and  candle-flame  (230,232);  when  hot 
remove  it  from  the  flame,  and  still  forcibly  urging  a  stream 


COMMINUTION.  627 

of  air  upon  it,  observe  how  it  continues  to  burn  until  nearly 
the  whole  is  consumed. 

[46.]  Heat  a  globule  of  antimony  as  just  described,  then 
drop  it  from  a  height  of  five  or  six  feet,  upon  a  sheet  of 
paper,  and  observe  its  brilliant  combustion,  and  the  trains 
of  oxide  it  leaves  on  the  paper.  Heat  another  globule,  and 
when  in  full  combustion  throw  it  through  the  air  against  a 
wall ;  remark  its  combustion  in  the  air  before  and  after  it  is 
broken. 

[47.]  Heat  a  small  platinum  crucible  (653)  red  hot,  by  a 
lamp  (233)  and  mouth  blow-pipe  (235). 

[48.]  Make  a  spirit-lamp  according  to  Mr  Phillip's  method 
(208),  and  complete  the  apparatus  by  making  a  temporary 
blow-pipe  from  a  piece  of  glass  tube  (221). 

[49.]  Fuse  platinum  on  charcoal  (240)  by  means  of  the 
oxy-alcohol  blow-pipe  (251).  Burn  a  cast-iron  sparable  in 
the  same  manner. 

[50.]  Compare  two  thermometers  at  high  and  low  tempe- 
ratures (281,  286). 

[51.]  Cool  a  thermometer  in  ice  and  water  (453,454), 
quickly  wipe  it,  and  then  immerse  it  in  a  jar  of  water  at 
common  temperatures,  to  ascertain  the  heat ;  and  observe 
the  time  required  (287).  Again,  cool  the  thermometer,  and 
wiping  it  quickly  as  before,  ascertain  the  temperature  of  the 
air  above  the  water,  and  noticing  the  time  required,  remark 
how  much  longer  it  is  than  in  the  first  experiment.  Hence 
learn  to  be  cautious  with  respect  to  the  time  allowed  for  a 
thermometer  to  acquire  its  proper  temperature  in  different 
situations  (286). 

V.  Comminution. . 

[52.]  Break  a  flint  in  the  hand,  supporting  it  upon  a  cloth 
or  glove  (315).  Break  a  small  pebble  on  the  anvil  (316). 

[53.]  Heat  flints  red  hot,  and  quench  them  in  water  (332); 
then  reduce  a  portion  to  an  impalpable  powder  (323,  330). 

[54.]  Break  a  piece  of  flint  glass  in  a  mortar  (315);  reduce 
it  to  small  fragments  or  a  coarse  powder  (321);  then  pulve- 
rize a  small  portion  very  finely  (3'23,  330);  afterwards  place 


628  PRECIPITATION. 

it  on  turmeric  paper,  and  moistening  it,  render  the  alkali 
evident  (624).* 

[55.]  Rub  a  piece  of  white  marble  of  about  400  grains  in 
weight  into  an  impalpable  powder  (329,  330);  reduce  half  as 
much  muriate  of  ammonia  also  to  fine  powder  (319,323); 
mix  the  two  well  together  (326),  for  experiment  99. 

[56.]  Make  an  intimate  mixture  (327)  of  equal  parts  by 
weight  of  muriate  of  ammonia  and  quicklime ;  observe  the 
ammonia  evolved  even  at  common  temperatures  (624,  626); 
then  use  it  in  experiment  211. 

[57.]  Break  and  pulverize  some  charcoal  (332)  for  expe- 
riments 174,  181,  183. 

[58.]  Pulverize  a  brittle  metallic  ore,  as  sulphuret  of  cop- 
per, or  of  lead,  or  native  oxide  of  iron  (321,  323),  and  weigh 
100  grains  (61)  for  analysis. 

[59.]  Before  using  the  common  salt  of  experiment  40, 
pulverize  it  (340)  to  prevent  decrepitation.  V 

[60.]  Weigh  200  grains  of  white  marble  in  lumps  (52); 
pulverize  it  very  finely  (323,  330);  then  collect  it  together 
(334),  and  again  weigh  it  (61),  and  ascertain  how  much  is 
lost  by  dispersion  or  adhesion  to  the  mortar.  The  loss  ought 
to  be  very  small. 

[61.]  Pulverize  (332,  321,  323)  and  levigate  (344)  a  piece 
of  felspar  or  slate,  so  as  to  obtain  an  uniformly  fine  powder. 

[62.]  Rub  and  wash  crude  platinum  (344,  348),  for  the 
.  purpose  of  separating  the  black  particles  from  those  which 
are  bright  and  metallic. 

[63.]  Dissolve  a  silver  coin  in  nitric  acid  (373,  380),  dilute 
the  solution,  and  precipitate  the  metal  in  a  finely  divided 
state  (356),  by  a  plate  of  copper. 

[64-]  Dissolve  the  washed  platinum  of  experiment  62  in 
nitro-muriatic  acid  (373,  383),  made  by  mixing  five  measures 
of  strong  muriatic  acid,  one  measure  of  strong  nitric  acid, 
and  three  measures  of  water  together,  precipitate  the  solution 
by  muriate  of  ammonia  (509),  wash  and  dry  the  precipitate 
(553,  539,  601),  then  decompose  a  part  of  it  by  heat  (670) 

*  An  experiment  due  to  Mr  Griffiths.    Quar.  Jour.  xx.  p.  259, 


GRANULATION SOLUTION DIGESTION — INFUSION.       629 

in  an  earthenware  crucible  (642),  so  as  to  produce  platinum 
in  a  spongy  state  (356).  Test  its  state  of  division  by  throw- 
ing a  jet  of  hydrogen  upon  it  (820);  although  perfectly  cold 
it  will  become  hot,  causing  the  ignition  of  the  gas:  the  rea- 
diness with  which  this  will  take  place  will  depend  on  the 
sponginess  and  lightness  of  the  platinum. 

[65.]  Granulate  some  zinc  (351),  that  it  may  be  ready 
for  the  preparation  of  hydrogen  gas  in  future  experiments. 
If  the  heat  of  the  fused  zinc  be  moderate,  the  resulting 
pieces  of  metal  will  be  thicker  than  if  the  heat  be  much 
higher.  Granulate  some  thus  raised  to  a  high  heat  and 
almost  ready  to  burn,  the  metal  will  be  almost  in  films;  dry 
it  (590),  and  then  break  it  down  in  a  mortar  (315,  321),  for 
the  purpose  of  preparing  carbonic  oxide  gas  in  future  expe- 
riments. 

VI.  Solution.    Digestion.   .Infusion. 

[66.]  Examine  the  solubility  of  crystals  of  sulphate  of  pot- 
assa,  sulphate  of  soda,  borax,  and  sugar  (361).  The  first  is 
difficultly  soluble:  observe  the  effects  in  all,  and  note  the 
absence  of  similar  -effects,  when  an  insoluble  substance  is 
immersed  in  the  fluid. 

[67.]  Examine  corrosive  sublimate  as  to  its  solubility  in 
water  (361);  then  dissolve  some  common  salt  or  muriate  of 
ammonia  in  the  water,  and  again  examine  the  solubility  of 
the  corrosive  sublimate  (361);  the  difference  occasioned  by 
the  salt  will  be  very  considerable. 

[68.]  Make  a  saturated  solution  of  nitre  in  water  without 
heat  (375)  by  trituration  in  a  mortar.  Then  to  each  pint 
add  about  four  ounces  of  crystallized  nitre,  dissolve  it  by  the 
application  of  heat  (369,  381)$  and  set  the  solution  aside  to 
crystallize,  as  in  experiment  127. 

[69.]  Dissolve  common  salt  in  common  water  in  a  tube, 
for  the  purpose  of  obtaining  evidence  that  air  is  expelled 
during  the  solution  (366). 

[70.]  Mix  together  nearly  equal  quantities  of  suga*r,  mar- 
ble, and  sand,  in  a  mortal  (327).  Take  about  an  ounce  of 
the  mixture,  and,  by  means  of  cold  water,  dissolve  but  the 
sugar  (368,  374);  collect  the  washed  residue  (539),  which 


630  SOLUTION — DIGESTION — INFUSION. 

need  not  be  dried,  and  subject  it  to  the  action  of  diluted  mu- 
riatic acid,  to  dissolve  the  carbonate  of  lime  (372,  409);  and 
having  removed  the  solution  formed  by  washing  (540,  &c.), 
nothirrg  but  the  sand  will  remain.  A  separation  and  imper- 
fect analysis  of  the  mixture  will  thus  be  made. 

[71.]  Dissolve  a  crystallized  and  clean  carbonate  of  baryta 
in  pure  muriatic  acid  in  an  evaporating  basin  (381,  409), 
containing  excess  of  the  carbonate,  so  that  the  solution  shall 
be  neutral  (624);  pour  off  the  solution  formed  (397),  and 
add  fresh  acid ;  proceed  in  this  manner  until  the  carbonate 
be  nearly  all  dissolved;  filter  the  solution  (536),  pour  it  into 
a  clean  bottle  by  a  rod  (398)  or  funnel  (436),  and  preserve 
it  for  use  as  a  test. 

[72.]  Boil  a  few  fragments  of  gum  mastic  in  a  tube  with 
alcohol  (405)  under  pressure  (99,  919).  "When  this  solution 
is  diluted  with  more  alcohol,  so  as  to  diminish  the  quantity 
of  mastic  to  70  grains  in  half  a  pint,  it  forms  an  excellent 
wash,  as  Mr  Hatchett  has  shown,  for  fixing  chalk  and  pencil 
drawings. 

[73.]  Weigh  one  hundred  grains  of  pure  dry  white  marble 
in  small  fragments  (52,  61),  put  them  into  a  Florence  flask 
(395,  435),  with  two  or  three  ounce  measures  of  water.  Put 
about  one-half  or  two-thirds  of  an  ounce  measure  of  strong 
muriatic  acid  into  a  test  glass,  and  adding  its  bulk  of  water, 
stir  them  well  together:  then  counterpoise  (64,  65)  the  test- 
glass  and  the  Florence  flask  with  their  cootents,  putting 
both  into  the  scale  at  once,  the  flask  on  the  glass.  This 
done,  pour  the  diluted  acid  into  the  flask  (399),  using  no 
funnel,  rod,  or  other  means,  but  taking  care  that  no  acid 
escape  down  the  outside  of  the  vessel.  It  is  not  requisite 
that  all  should  be  poured  out  of  the  glass,  but  that  none 
should  be  lost  to  these  vessels.  Attend  to  the  effervescence, 
that  no  liquid  be  thrown  off  (396):  when  all  the  solid  matter 
is  dissolved,  expel  the  atmosphere  of  carbonic  acid  by  blow- 
ing in  air  through  a  tube,  and  again  weigh  the  vessels,  ob- 
serving the  loss  of  weight  due  to  the  expulsion  of  the  car- 
bonic acid  (59).  It  should  be  4^grains.  Leave  it  a  night, 
and  observe  the  difference,  if  any,  next  morning. 

[74.]  Dissolve  pulverized  sulphuret  of  iron  (323)  in  nitro- 


SOLUTION DIGESTION INFUSION.  631 

muriatic  acid  (409,  414),  under  a  hood  (391,  &c.),  that  the 
fumes  may  be  carried  away.  When  dissolved,  examine  small 
portions  of  the  solution  (400,  505)  by  ammonia,  to  show  the 
presence  of  oxide  of  iron,  and  by  the  muriate  of  baryta  of 
experiment  71,  to  show  the  sulphuric  acid  formed  during 
the  action. 

[75.]  After  observing  the  precipitation  of  the  oxide  of 
iron  from  the  above  solution  by  ammonia,  take  another  por- 
tion of  the  solution,  add  tartaric  acid  to  it  (412),  and  then, 
on  adding  the  ammonia,  it  will  be  found  that  no  precipitate 
will  take  place. 

[76.]  Put  a  solution  of  chromate  of  potassa  into  a  flask, 
and  add  a  portion  of  sulphuric  acid;  the  colour  will  be  very 
much  deepened  and  rendered  almost  red;  add  a  little  alcohol 
and  apply  heat  (416,  386),  when  on  a  sudden  the  colour  will 
change  to  green.  Upon  examination  it  will  be  found  that 
the  chromic  acid  has  lost  oxygen,  has  become  chromic  oxide, 
and  has  formed  sulphate  with  the  acid  present. 

[77.]  Dissolve  caustic  lime  in  water  in  a  close  vessel  (372), 
evaporate  a  certain  volume  of  the  solution  to  dryness  (596), 
and  note  the  quantity  of  earth  left.  Then  make  a  similar 
solution  of  lime  in  a  vessel  with  water,  containing  one  half 
its  weight  of  white  sugar  (412);  take  the  same  volume  of  this 
solution  as  before,  evaporate  to  dryness,  and  burn  off  the 
sugar  (653,  666)  in  a  crucible;  ascertain  the  weight  of  lime 
left,  and  observe  how  much  it  surpasses  the  former  quantity, 
in  consequence  of  the  solubility  conferred  by  the  sugar. 

[78.]  Digest  some  pale  Peruvian  bark  in  four  times  its 
weight  of  water  (369,417);  after  the  infusion  has  stood  some 
time  pour  off  the  clear  part  (397),  and  when  cold,  test  it  by 
tincture  of  galls  and  by  carbonate  of  potassa  (506).  The 
precipitate  will  be  proportionate  to  the  quantity  of  cinchona* 
(cinchonina)  in  the  bark. 

[79.]  Make  a  strong  infusion  (419)  of  bruised  nut  galls, 
and  set  it  aside  in  covered  jars  (566)  for  a  month  or  two 
(1302);  at  the  end  of  that  time  a  quantity  of  crystalline  mat- 

*  Gallic  acid  forms  with  cinchonina  a  salt  soluble  only  with  excess  of  acid, 
therefore  tincture  of  galls  throws  down  gallate  of  cinchonina.— ED. 


632  DISTILLATION — SUBLIMATION. 

ter  will  be  observed  at  the  bottom  of  the  fluid,  which  may 
be  collected  (549),  purified  by  crystallization,  &c.  (563, 564), 
and  will  be  nearly  pure  gallic  acid. 

[80.]  Pour  water  or  a  solution,  by  means  of  a  rod  (397), 
without  spilling.  Pour  out  exactly  one  ounce  measure  of 
muriatic  acid  in  the  same  way  (120,  398),  so  steadily  as  to 
make  the  fluid  coincide  with  the  mark  on  the  measure  at 
once,  and  without  addition  or  abstraction.  Add  this  acid 
carefully  to  the  carbonate  of  baryta  in  experiment  71,  wash- 
ing out  the  last  portions  from  the  measure  by  water  (402). 
In  this  way  acquire  the  facility  of  apportioning  exact  quan- 
tities, and  of  adding  every  particle  of  them  to  other  sub- 
stances when  required. 

VII.  Distillation,  Sublimation,  fyc. 

[81.]  Distil  common  water  in  a  metal  still  (424),  or  in  a 
glass  retort  (428,  438),  condensing,  if  requisite,  by  a  funnel 
and  paper  (465),  or  using  a  globe  of  sufficient  capacity  (447) 
to  condense  all  the  vapour.  Apply  the  heat  of  a  lamp  (212, 
386),  or  hot  air  (262),  or  a  small  charcoal  fire  (158,  386). 

[82.]  Distil  half  a  pint  of  wine  in  a  glass  retort  (465),  until 
three-fourths  of  the  flu-id  have  passed  over.  Change  the 
receiver  or  flask  (467)  when  about  an  eighth  has  been  dis- 
tilled, for  the  purpose  of  keeping  apart  the  first  strong  spirit. 
Introduce  a  few  slips  of  platinum  foil,  and  a  piece  or  two 
of  cork  (441),  to  facilitate  the  formation  of  vapour*  Use  any 
of  the  sources  of  heat  mentioned  in  the  last  experiment. 

[83.]  Distil  nitric  acid  from  nitre  and  sulphuric  acid  in  a 
glass  retort  (475).  Introduce  the  acid  in  a  neat  manner 
(436);  apply  heat  by  means,  of  a  sand  bath  (176);  and  con- 
dense in  the  manner  already  described  (476). 

[84.]  Distil  dry  nitrate  of  lead  in  a  glass  retort  (463)  by  the 
heat  of  a  crucible  furnace  (386),  condense  the  products  in 
small  dry  flasks  (461),  tubes  (929),  or  bottles  (461),  cooled 
by  a  refrigerating  mixture  (454).  Nitrous  acid  will  pass 
over  and  be  procured  in  the  fluid  state. 

[85.]  Rectify  some  sulphuric  acid  in  a  glass  retort  (429, 
439)  over  a  sand  bath  (176),  or  crucible  furnace  (158).  Use 
platinum  foil  to  facilitate  the  evolution  of  vapour  (444). 


DISTILLATION SUBLIMATION.  633 

Condense  the  vapour  in  a  flask  (447),  supported  in  the  open 
air  (483),  and  not  purposely  cooled  by  ice  or  freezing  mix- 
tures. 

[86.]  Put  two  ounces  of  acetate  of  potash  into  a  retort 
(435),  with  its  weight  of  strong  sulphuric  acid  5  distil,  using 
a  flask  as  a  receiver  (446),  containing  one  ounce  of  diluted 
water.  Heat  the  retort  by  a  chemical  lamp  (212),  and  cool 
the  flask  by  a  basin  of  water  (447).  A  solution  of  pure 
acetic  acid  will  be  obtained. 

[87.]  Distil  sulphurous  acid  as  already  described  (448). 
Heat  the  retort  by  a  chemical  lamp  (212);  cool  the  little  tube 
receivers  (929)  in  a  well  prepared  refrigerating  mixture  (454), 
and  ultimately  seal  them  up  (1191). 

[88.]  Distil  a  portion  of  muriatic  acid  from  common  salt, 
mixed  with  nearly  its  weight  of  sulphuric  acid,  previously 
diluted  with  an  equal  weight  of  water  (475).  Apply  heat  by 
a  sand-bath  or  low  charcoal  fire  (163),  and  use  the  tube  of 
safety  (478)  to  prevent  absorption.  Receive  the  products 
into  vessels  containing  a  little  water.  Test  the  acid,  which 
will  thus  be  prepared,  by  muriate  of  baryta  (506),  to  ascer- 
tain whether  any  sulphuric  acid  has  passed  over  or  not. 

[89].  Distil  a  little  isinglass  or  horn,  or  even  slips  of  lea- 
ther, in  a  small  coated  glass  retort  (489)  by  a  crucible  fur- 
nace fire  (490).  Receive  the  products  in  successive  portions, 
using  glass  flasks  as  condensers  (446),  employing  a  little 
water  at  first  in  them  to  dissolve  the  ammonia  formed.  Ob- 
serve the  production  of  water,  ammonia,  fetid  gas,  tar,  and 
empyreumatic  matter;  heat  the  retort  to  redness  (490),  so 
that  when  cold  and  broken,  the  charcoal  within  may  be  well 
formed.  Remark  its  peculiar  appearances,  its  cellular  state, 
its  lustre,  great  hardness,  &c.,  and  its  difficult  incineration 
in  the  air  (204). 

[90.]  Mix  the  finely  divided  zinc  of  experiment  65  with 
thrice  its  weight  of  powdered  marble  (323),  and  heat  the 
mixture  in  an  iron  (493)  or  an  earthenware  retort  (491),  for 
the  production  of  carbonic  oxide  (experiment  215);  a  dull 
red  heat  will  be  required,  and  may  be  obtained  either  by 
means  of  the  table-furnace  ,(494)  or  the  crucible-furnace, 
according  to  the  size  of  .the  retort  (490).  The  gas,  if  in- 
4  E 


634  DISTILLATION SUBLIMATION. 

flamed,  as  it  issues  from  the  mouth  of  the  retort,  will  burn 
with  a  fine  blue  colour. 

[91.]  Prepare  phosphorus  according  to  the  direction  con- 
tained in  elementary  works;  or  make  chloride  of  antimony, 
distilling  in  coated  glass  retorts  (489,  490). 

[92.]  Put  some  ether  into  a  tube,  close  the  mouth  of  the 
tube  by  the  finger  (766,  99),  and  heat  the  ether  until  it  is 
ready  to  boil  upon  opening  the  aperture  (919,  921);  remove 
the  tube  from  the  heat,  and  displace  the  finger  so  as  to  allow 
ebullition,  until  the  temperature  is  so  low  as  to  occasion  its 
cessation;  then  suddenly  drop  in  a  chip  of  dry  wood  (444), 
and  remark  how  powerfully  the  ebullition  is  renewed  by  it. 

[93.]  Make  a  freezing  mixture  of  ice  and  salt  (454),  put  it 
into  a  glass,  and  ascertain  whether  its  temperature  is,  as  it 
ought  to  be,  at  0°  Fahrenheit  (286).  Put  a  little  water  into 
a  thin  glass  tube  (910),  and  stir  the  mixture  by  means  of  it 
(454,  457).  The  water  will  be  frozen  solid  in  the  course  of 
two  or  three  minutes. 

[94.]  Introduce  a  little  metallic  arsenic  into  a  tube  (495, 
910),  apply  the  heat  of  a  spirit-lamp  (199),  and  sublime  the 
metal  so  as  to  form  bright  metallic  films  or  crusts  of  crystals 
at  pleasure  (935);  observe  the  temperature  at  which  it  sub- 
limes, and  the  degree  of  rapidity  with  which  it  condenses  on 
parts  more  or  less  heated.  Sublime  it  up  and  down  the  tube, 
so  as  to  obtain  command  of  it,  and  the  power  of  condensing 
it  in  this  or  that  part  of  the  tube  at  pleasure  (937). 

[95.]  Introduce  some  naphthaline  into  a  large  flask  or 
globe  (495),  place  it  on  a  warm  part  of  the  sand-bath  (171), 
and  allow  it  to  sublime  slowly;  close  the  mouth  of  the  vessel 
with  paper  (1253).  When  a  sufficient  quantity  has  sublimed, 
remove  the  vessel  carefully  on  one  side  till  all  is  cold,  then 
shake  out  the  crystals  and  examine  the  beauty  of  their  forms. 

[96.]  Sublime  iodine  in  the  same  manner  (495),  both 
quickly  and  slowly;  observe  the  beauty  of  the  forms  obtained 
in  the  latter  case. 

[97.]  Put  a  portion  of  calomel  into  a  Florence  flask  (495), 
and  sublime  it  into  the  upper  part  by  placing  the  bottom  in 
sand  (497),  on  a  hot  part  of  the  bath  (171);  nearly  a  red  heat 


PRECIPITATION.  635 

is  required.  When  sublimed  allow  the  vessel  to  cool :  cut  it 
by  an  iron  ring  (1212),  and  examine  the  sublimed  mass. 

[98.]  Sublime  a  little  indigo  in  the  manner  described 
(499).  It  will  be  obtained  in  very  minute  but  beautiful 
crystals. 

[99.]  Take  the  mixture  made  in  experiment  55,  put  it  into 
a  Florence  flask,  and  sublime  it  by  a  sand-bath  or  chemical 
lamp  (386).  Incline  the  flask  and  pass  its  neck  through  a 
cork  (466)  into  a  cool  receiver  (495),  or  into  the  end  of  a 
wide  tube  that  may  be  cooled  by  the  air  (497),  or  if  necessary 
by  water  (468).  Carbonate  of  ammonia  will  be  obtained. 

VIII.  Precipitation. 

[100].  Neutralize  the  solution  left  by  experiment  73  with 
ammonia  (629),  adding  a  slight  excess  of  the  alkali,  then  add 
carbonate  of  ammonia  until  all  the  lime  be  precipitated  (513); 
collect  it  together  (521),  wash  it  (553),  dry  it  (554, 601),  and 
weigh  it.  It  should  be  exactly  100  grains,  or  the  quantity 
at  first  dissolved. 

[101.]  Select  a  marie  or  a  lias,  limestone,  pulverize  it, 
(323),  weigh  a  given  quantity  (61),  act  upon  it  by  diluted 
muriatic  or  acetic  acid  at  ordinary  temperature  (375)  until 
all  effervescence  cease;  wash  off  (553)  and  preserve  the  so- 
lution as  well  as  the  insoluble  portion;  dry  the  latter  (601), 
and  weigh  it  (6^,  52).  Precipitate  the  solution  by  ammonia 
and  carbonate  of  ammonia  (521)  as  above,  and  having  washed 
(553)  the  carbonate  of  lime  formed,  dry  and  weigh  it  (64 
682,  &c.).  Its  quantity  is  the  same  as  the  quantity  of  car- 
bonate of  lime  in  the  marie,  and  with  the  quantity  of  residue 
should  make  up  the  whole  weight  of  the  marie  used.  An 
analysis  of  the  marie  will  thus  be  effected. 

[102].  Precipitate  a  portion  of  muriate  of  baryta  in  solu- 
tion by  sulphate  of  soda  (509,  513,  518),  wash  the  precipi- 
tate well  (540),  dry  it  and  heat  it  red  hot  (666)  in  a  platinum 
crucible. 

[103].  Weigh  out  50  grains  (51)  of  crystallized  muriate 
of  baryta,  dissolve  it  in  distilled  water  (368),  precipitate  the 
acid  by  nitrate  of  silver  (513,  517),  and  after  separating  all 
the  soluble  matter  from  the  insoluble  by  repeated  washing 


636  PRECIPITATION. 

(553)  dry  (602),  and  weigh  the  latter,  which  is  chloride  of 
silver;  it  ought  to  amount  to  58.87  grains  (1318).  Then 
proceed  to  precipitate  the  soluble  portion  by  sulphate  of  soda 
(513,  518)  to  separate  the  baryta  as  a  sulphate;  wash  (553, 
555),  dry,  and  heat  this  substance  to  redness  (666),  then 
weigh  it  (51,  682):  it  ought  to  be  47.42  grains  (1318). 

[104.]  Dissolve  a  silver  coin  (372,  380),  precipitate  the 
silver  by  adding  a  solution  of  common  salt  (513,  517),  wash 
and  dry  the  pure  chloride  of  silver  thus  formed,  and  use  it 
hereafter  in  experiment  180,  for  the  preparation  of  pure 
silver. 

[105.]  Precipitate  the  muriates  from  a  mineral  water  by 
adding  solution  of  nitrate  of  silver  (517,  514),  wash,  dry, 
and  weigh  the  precipitate  (51,  64),  and  estimate  the  quan- 
tity of  muriatic  acid  present  in  a  given  quantity  of  the  water, 
by  referring  to  the  scale  of  equivalents  (1318). 

[106.]  Take  a  portion  of  the  ferruginous  solution  of  ex- 
periment 74,  or  any  other  solution  of  iron,  and  throw  down 
the  oxide  of  iron  by  ammonia  (509,  629);  wash,  dry,  heat  to 
redness  (670),  and  weigh  the  oxide  obtained.  If  the  iron  in 
the  solution  be  not  in  the  state  of  peroxide,  first  render  it  so 
(414)  by  a  little  nitric  acid  and  heat. 

[107.]  Take  a  small  portion  of  the  same  ferruginous  solu- 
tion, and  precipitate  it  by  the  ferro-prussiate  of  potassa  (509, 
519).  A  blue  precipitate  will  be  obtained,  which  is  then  to 
be  repeatedly  washed  (553).  As  long  as  much  of  the  solu- 
ble matter  remains,  the  washing  water  and  the  precipitate  will 
easily  separate  (519),  but  as  the  washing  approaches  com- 
pletion it  will  be  found  that  the  pure  water  added  dissolves 
the  blue  precipitate.  Remark  this  effect,  and  then  add  a 
little. pure  muriatic  acid  (555);  this  will  immediately  cause  as 
complete  a  separation  of  the  prussian  blue  as  before,  and  the 
washing  fluid  will  become  nearly  colourless. 

[108.]  Dissolve  100  grains  of  crystallized  sulphate  of  cop- 
per in  water  (375),  immerse  a  clean  plate  of  soft  iron  to  pre- 
cipitate the  copper  in  the  metallic  state  (522);  when  the 
precipitation  is  completed,  collect  the  metal,  wash,  dry,  and 
weigh  it  (553,  602,  51);  its  weight  should  be  25.6  grains. 
Then  dissolve  it  carefully  in  nitric  acid.  Precipitate  the  so- 


FILTRATION DECANTATION WASHING.  637 

lution  by  excess  of  caustic  potassa,  applying  heat  at  the  same 
time  (516),  till  the  precipitate  becomes  a  dense  black  pow- 
der. Then  wash  and  dry  it,  and  heat  it  to  300°  or  400° 
(264),  afterwards  weigh  it;  it  ought  to  equal  32  grains  (1321). 

[109.]  Test  a  weak  solution  of  potassa  by  muriate  of  pla- 
tinum (506). 

[110.]  Examine  the  distilled  water  of  the  laboratory  by 
various  precipitating  tests.  Previously  evaporate  three  or 
four  pints  to  half  a  pint  (594,  597),  to  render  any  salts  that 
may  be  present  more  sensible  to  the  action  of  the  re-agents. 

IX.  Filtration,  Decantation,  Washing. 

[111.]  Burn  400  grains  of  the  filtering  paper  in  use  in  the 
laboratory  (530),  and  ascertain  the  quantity  by  weight  of  the 
ashes  left  (531 ).  Wash  them  well  with  water  (542),  dry  the 
insoluble  portion  (609),  and  ascertain  its  amount. 

[112,]  Pass  a  quarter  of  a  pint  of  distilled  water  several 
times  in  succession  through  the  same  double  filter  of  paper 
(537)  so  as  to  wash  out  every  thing  soluble  (542);  evaporate 
the  water  to  a  fourth  of  its  bulk  (591),  then  test  it  for  differ- 
ent substances,  the  presence  of  which  has  been  suspected  in 
the  paper,  as  sulphates,  muriates,  &c.  (504). 

[113].  Filter  some  foul  or  turbid  water  through  a  folded 
filter  (534,  536),  remarking  that  it  pass  through  perfectly 
clear. 

[114.]  Filter  a  turbid  solution  (539),  as  that  obtained  from 
the  marie  or  lias  limestone  in  experiment  101,  washing  out 
all  the  soluble  matter  from  the  filter  (542). 

[1 15.]  Separate  a  precipitate  of  oxide  of  iron  by  filtration, 
experiment  106,  or  one  of  sulphate  of  baryta,  experiment  102, 
(540),  washing  it  in  the  filter  until  the  water  that  will  pass 
in  the  first  case  contains  no  trace  of  muriatic  acid  (504)  or 
other  soluble  matter,  and  in  the  second  case  no  trace  of  sul- 
phuric acid  resulting  from  the  excess  of  sulphate  of  soda  used 
(506). 

[116.]  Wash  carbonate  of  lime  precipitated  as  in  experi- 
ment 101,  or  in  any  other  way  (521),  until  all  traces  of  solu- 
ble matter  are  removed  (540),  stirring  up  the  carbonate  by 
the  bottle  (541,  402)  or  the  washer  (547). 


638  FILTRATION — DECANTATION WASHING. 

[117.]  Dissolve  four  ounces  of  crystallized  Glauber's  salt 
in  two  ounces  of  water  by  heat  (380)  in  a  flask,  filter  the  solu- 
tion whilst  hot  (544)  to  avoid  crystallization  in  the  pores  of 
the  paper,  and  cover  the  whole  up  with  a  glass  vessel  or 
paper  cover  (1343) 

[118.]  Filter  a  portion  of  heated  hog's  lard  or  tallow 
through  paper  (544). 

[119].  Mix  up  equal  measures  of  oil  and  water;  separate 
these  bodies  one  from  the  other  by  filtration  of  the  water 
[543]  through  a  wet  paper  filter. 

[120.]  Dissolve  five  grains  of  carbonate  of  baryta  by  means 
of  a  little  muriatic  acid  in  a  small  evaporating  dish  (369), 
pass  the  solution  through  a  small  filter  without  a  funnel  (546), 
test  for  the  baryta  on  a  glass  plate  (1348),  using  but  little  of 
the  solution.  Precipitate  the  rest  by  carbonate  of  ammonia 
in  a  tube  (910),  separate  the  carbonate  on  a  small  paper 
filter  (546),  wash  it  on  the  filter  by  the  dropping  bottle  till 
pure  (404,  547),  then  dry  it  (609),  and  ascertain  with  how 
small  a  loss  the  whole  has  been  effected  (51,  59). 

[121.]  Dilute  an  ounce  of  port  wine  with  three  ounces  of 
water;  set  aside  a  small  quantity  of  it  and  boil  the  rest  (386) 
with  an  ounce  of  animal  charcoal  (61)  for  ten  minutes,  filter 
it  (539,  543),  and  by  comparing  the  colour  with  that  of  the 
reserved  portion,  observe  how  powerfully  the  charcoal  has 
acted  in  removing  it. 

[122.]  Collect  some  charcoal  ashes  from  the  crucible  fur- 
nace (158),  and  lixiviate  them  (420).  Examine  the  solution 
for  alkali  (624)  and  other  substances. 

[123.]  Precipitate  a  solution  of  two  ounces  of  alum  in 
water  by  carbonate  of  potassa  (504,  629);  wash  the  precipitate 
in  much  water  (553),  mixing  it  up  well  with  a  tube  (514); 
when  settled,  decant  off  the  fluid  (397,  550),  and  wash  the 
precipitate  again  (553);  when  subsidence  has  taken  place, 
remove  the  fluid  by  a  syphon  (550),  and  thus  proceed  till  no 
trace  of  alkali  or  sulphuric  acid  exist  in  the  washing  fluid. 

[124.]  Put  water,  oil,  and  mercury,  into  the  same  glass. 
Separate  them  by  the  funnel  (557)  as  accurately  as  possible, 
receiving  them  into  different  vessels. 

[125.]  Mix  a  little  oil  of  turpentine  and  water  together  in 


CRYSTALLIZATION.  639 

a  tube  (910),  then  separate  them  by  the  little  vessel  before 
described  (559). 

[126.]  Put  some  globules  of  mercury  at  the  bottom  of 
some  water  or  sulphuric  acid;  remove  them  by  means  of  the 
mouth  and  a  pointed  tube  (558),  or  by  the  use  of  a  little 
glass  syringe  (560),  and  transfer  them  in  a  clean  dry  state  into 
a  separate  vessel.  In  the  same  manner  remove  a  few  drops 
of  water  from  the  bottom  of  some  oil. 

X.  Crystallization. 

[127.]  Make  a  solution  of  crude  or  common  nitre  on  the 
sand-bath,  exp.  68,  of  such  strength  as  to  crystallize  when 
cold  (379);  filter  it  (544);  then  set  it  aside  in  a  deep  basin 
(564)  to  crystallize  slowly. 

[128.]  In  the  same  manner  crystallize  warm  solutions  of 
alum,  and  of  Glauber's  salt  (564),  previously  trying  the  pro- 
per strength  of  the  solutions  on  a  glass  plate  (379);  cover  the 
solutions  with  paper  cones  (1343)  or  flannel. 

.  [129.]  Crystallize  acetate  of  lead  (563)  by  cooling  a  hot 
solution. 

[130.]  Crystallize  muriate  of  soda  (565)  by  the  slow  eva- 
poration of  a  cold  saturated  solution  (378). 

[131.]  Prepare  a  solution  of  alum  for  crystallization  by 
diminution  of  temperature  (378,  563);  hang  a  thread  across 
it,  or  leave  in  it  a  glass  rod  with  a  thread  wound  round  it, 
and  observe  the  greater  tendency  to  deposition  on  the  one 
substance  than  the  other. 

[132.]  Dissolve  a  little  sulphate  of  magnesia  in  water  in  a 
.capsule  (575);  evaporate  drops  of  it  slowly  on  a  glass  plate 
(1348),  and  examine  the  crystals  (575,  580).  Do  the  same 
with  alum,  nitre,  Glauber's  salt,  phosphate  of  soda,  and  com- 
mon salt;  and  observe  with  what  facility  the  crystals  of  these 
salts  may  be  obtained  from  small  quantities  of  solutions,  and 
examined,  so  as  to  determine  their  characters  and  the  nature 
of  the  substances  crystallized. 

[133.]  Transform  several  small  crystals  of  sulphate  of 
nickel  into  a  large  one  (570). 

[134.]  Crystallize  sulphur,  bismuth,  or  lead  (578)  in  a  cru- 
ble,  by  fusion,  and  partial  solidification. 


640  EVAPORATION DESICCATION. 

[135.]  Crystallize  naphthaline  by  sublimation  in  a  globe 
or  flask  (579). 

XI.  Evaporation.    Desiccation. 

[136.]  Evaporate  a  solution  of  common  salt  gradually  to 
dryness  (583,  565),  covering  the  vessel  containing  it  with 
paper  (566)  to  keep  out  the  dirt. 

[137.]  Evaporate  a  solution  of  sulphate  of  copper,  so  that 
it  shall  crystallize  on  cooling  (379,  564),  make  it  thus  give 
successive  crops  of  crystals  by  successive  processes,  till  all 
the  salt  is  separated. 

[138.]  Procure  some  spring  water,  as  the  deep  well  water 
of  London;  evaporate  a  portion  to  dryness,  in  a  basin  (369), 
on  the  sand-bath  (598,  381)  or  otherwise  (590),  and  then 
test  the  residue  by  a  little  water  and  turmeric  paper  for  free 
alkali  (624),  or  by  other  agents  for  the  detection  of  other 
substances. 

[139].  Evaporate  some  of  the  same  water  by  boiling  it 
away  in  a  Florence  flask  (594),  until  reduced  to  a  very  small 
quantity;  then  test  the  remaining  portion  (504). 

[140.]  Evaporate  a  part  of  the  same  water  in  a  platinum 
crucible  (597),  and  heat  the  residue  (666),  to  ascertain  whe- 
ther it  be  changeable  by  such  treatment  or  not. 

[141.]  Evaporate  an  infusion  of  a  vegetable  substance  to 
dryness  (419),  so  as  to  obtain  the  extract  uninjured  by  heat 
(599). 

[142].  Dissolve  an  impure  carbonate  of  baryta  in  muriatic 
acid  added  until  in  slight  excess  (369,  624);  evaporate  the 
solution  to  dryness  (596),  to  dissipate  the  excess  of  acid, 
stirring  the  product  when  it  becomes  thick  or  solid  (592), 
to  prevent  its  dispersion. 

[143.]  Heat  crystallized  Glauber's  salts  in  a  basin  (601) 
to  drive  off  all  the  water  (602),  and  reduce  the  substance  to 
an  anhydrous  state.  Stir  the  melted  salts  with  a  rod,  until 
they  become  nearly  solid  (592),  and  then  rub  them  with  a 
pestle,  that  all  parts  may  be  pulverized  and  dry  (592). 

[144].  Evaporate  the  moisture  from  washed  carbonate  of 
lime  (521),  in  a  basin  (369),  covering  the  substance  with 
another  basin  (596),  during  the  operation,  to  keep  out  the 


COLOURED  TESTS NEUTRALIZATION.          641 

dirt.  Test  the  dryness  of  the  carbonate  by  a  cold  glass 
plate  (603). 

[145.]  Dry  a  little  pulverized  black  oxide  of  manganese  on 
the  sand-bath  (173),  or  over  a  lamp  (212):  lest  the  dryness 
by  a  glass  plate  (602). 

[146.]  Evaporate  a  solution  of  sugar  in  water  (375),  by 
Leslie's  process  (583),  until  it  be  as  dry  as  possible. 

[147.]  Freeze  water  by  evaporation  by  means  of  Leslie's 
process  (583).  * 

[148.]  Dry  a  part  of  the  vegetable  solution  of  exp.  141, 
by  sulphuric  acid  or  other  bodies  (589)  under  a  receiver,  no 
exhaustion  being  made. 

[149.]  Dry  a  filter  and  its  contained  precipitate,  as  that 
of  exp.  101,  on  a  tin  plate  (609)  over  a  lamp  or  sand-bath. 

[150.]  Dissolve  2  grains  of  carbonate  of  soda  in  water  in 
a  watch  glass  (400);  add  excess  of  muriatic  acid,  evaporate 
to  dryness  (603);  re-dissolve  and  re-evaporate,  so  as  to  obtain 
small  well-formed  crystals  in  the  glass  (568);  observe  their 
forms  (580),  which  will  be  those  of  chloride  of  sodium  or 
common  salt.  ,  . 

[151.]  Dry  some  precipitates  on  filters  (542),  in  a  box 
(608)  or  air  jar,  into  which  heated  air  is  thrown  from  a  lamp 
(270)  or  by  some  other  arrangement  (269). 

[152.]  Drain  the  crystals  of  exp.,  127  err  128,  in  a  funnel 
(613),  aiding  the  desiccation  by  a  current  of  air  (614).  * 

XII.  Coloured  Tests.    Neutralization. 

[153.]  Dilute  10  grains  (67,  51)  of  strong  sulphuric  acid 
until  it  will  scarcely  affect  litmus  paper  (624),  comparing  it 
with  water  (625);  observe  and  estimate  the  quantity  of  water 
required  for  the  dilution.  Then  heating  a  little  of  the  diluted 
acid  in  a  basin  or  tube,  remark  how  much  further  the  dilution 
may  be  carried,  and  yet  the  acidity  remain  sensible.  Leave 
little  pieces  of  litmus  paper  in  the  liquor  for  this  purpose 
(627). 

[154.]  Try  the  effects  of  different  acids  (615)  on  the  blue 
test  solution  (616).'^  , 

[155.]  Try  alkalies  and  carbonated  alkalies  on  turmeric 
(624)  or  reddened  litmus  paper  (626);  remark  how  little  of 

•  ^  4  F 


642  COLOURED  TESTS — CRYSTALLIZATION. 

these  substances  produces  a  sensible  effect.  Try  lime  and 
baryta  water  in  the  same  manner,  but  notice  the  restoration 
of  the  colour  on  the  turmeric  paper  as  the  earth  becomes 
carbonated  by  contact  of  the  air. 

[156.]  Test  the  air  of  the  laboratory  for  acid  fumes  by 
litmus  paper  (619,  623). 

[167.]  Try  the  effect  of  boracic  acid  on  turmeric  paper 
(630),  and  afterwards  the  effects  of  other -acids  on  the  same 
places.  Try  the  effect  of  a  mixture  of  boracic  acid  and  other 
acids  upon  turmeric  paper  (630),  and  compare  it  with  the 
effects  of  the  pure  acids. 

[158.]  Test  ammonia,  either  in  solution  or  in  vapour,  by 
turmeric  paper  (622,  624),  and  observe  the  transient  effect 
produced  by  this  alkali. 

[159.]  Heat  a  piece  of  isinglass  in  a  small  tube  (910,  954), 
and  test  the  vapours  given  off  at  the  mouth  of  the  tube  by 
turmeric  paper,  for  ammonia  (622). 

[160.]  Render  a  portion  of  diluted  sulphuric  acid  neutral 
by  the  addition  of  a  solution  of  carbonate  of  potassa,  apply- 
ing heat  during  the  operation  (628),  and  ascertaining  the 
state  of  the  solution  by  litmus  and  turmeric  papers  (624, 625). 

[161.]  Dilute  some  sulphuric  acid  to  a  given  strength 
(633.) 

[162.]  Lixiviate  half  a  pound  of  wood  or  charcoal  ashes 
(157,  420),  and  ascertain  by  the  diluted  sulphuric  acid  (633) 
and  alkalimeter  tube  (632),  how  much  alkali  they  contain 
(634). 

[163.]  Try  an  impure  alkali,  as  barilla  or  kelp,  in  the  same 
manner  (634,  638). 

[164.]  Precipitate  a  solution  of  the  persulphate  of  iron  by 
carbonate  of  ammonia  in  an  evaporating  basin  (369),  apply- 
ing heat,  and  adding  the  alkali  only  to  neutralization  (628, 
629).  Then  examine  the  solution,  and  it  will  be  found  that 
all  the  iron  will  have  been  separated  (504). 

[165.]  Make  a  solution  of  the  common  ore  of  manganese 
in  dilute  sulphuric  acid  (380);  filter  (539);  add  a  little  nitric 
acid,  and  apply  heat  (414)  to  peroxidize  the  iron  that  has 
been  dissolved ;  then  gradually  add  solution  of  carbonate  of 
ammonia  to  the  hot  solution  (628),  until  the  latter  is  neutral 


CRUCIBLE  OPERATIONS.  643 

(624,  625);  by  this  process  all  the  iron  will  be  precipitated, 
but  all  the  manganese  remain  in  solution. 

[166.]  Try  the  strength  of  a  diluted  pure  acetic  acid,  or  a 
specimen  of  distilled  vinegar,  by  a  piece  of  marble  (639). 

[167.]  Ascertain  the  strength  of  diluted  muriatic  acid  by 
a  similar  process  (640),  and  also  of  diluted  nitric  acid  (640); 
applying  heat  in  all  these  cases  to  expedite  the  action  (628), 
and  to-render  the  point  of  neutralization  distinct  (624). 

XIII.  Crucible  Operations. 

[168.]  Heat  some  flints  to  redness  in  a  Hessian  crucible 
(643,  670),  and  quench  them  in  water  (332),  to  prepare  them 
for  pulverization. 

[169.]  Convert  some  carbonate  of  lime  into  quick  lime  in 
an  earthenware  crucible  (642),  by  means  of  a  crucible  fur- 
nace. (158,  670),  and  flue  (165). 

[170.]  Fuse  a  portion  of  lead  in  an  earthenware  crucible 
(648,  662),  heated  in  a  crucible  furnace  (670).  After  con- 
cluding that  experiment,  fuse  a  portion  of  copper  in  another 
crucible  in  the  same  furnace  (670,  165),  and  ultimately,  if 
possible,  a  portion  of  cast-iron  in  a  third  crucible,  raising 
the  heat  for  this  purpose  to  the  highest  degree  (671,  168). 
Remark  the  difference  of  temperature  required  for  these 
operations,  and  also  the  powers  of  the  furnace  when  assisted 
by  the  flue  (165),  &c. 

[171.]  Fuse  400  grains  of  copper  in  an  earthenware  cru- 
cible (643)  heated  in  the  crucible  furnace  (158,  670),  and 
cover  the  metal  with  a  few  pieces  of  charcoal  (6S3).  When 
well  melted,  add  100  grains  of  zinc  in  fragments,  and  mix  it 
with  the  copper,  either  by  one  of  the  pieces  of  charcoal  or 
an  iron  rod  (683).  The  result  will  be  brass,  which  may 
either  be  poured  into  a  mould,  or  allowed  to  cool  in  the 
crucible. 

[172.]  Fuse  a  portion  of  steel  in  an  earthenware  cruci- 
ble, (643)  in  the  blast  furnace  (184,  673),  being  careful  to 
keep  the  carbonaceous  matter  from  contact  with  the  steel 
(674,  &c.) 

[173.]  Fuse  a  portion  of  pure  iron,  as  horse-shoe  nails,  in 
the  same  manner  in  the  blast-furnace  (679).  When  the 


644  CRUCIBLE  OPERATIONS. 

crucible  is  cold,  examine  the  button  of  iron  by  nitric  acid, 
to  ascertain  the  absence  of  carbonaceous  matter ;  for  this 
purp9se  the  surface  of  the  button  must  be  brightened  on 
one  part,  and  a  drop  of  dilute  nitric  acid  placed  on  the  spot. 
Being  wiped  off  a  few  minutes  afterwards,  it  should  leave 
no  black  stain,  but  the  metallic  iron  should  appear  pure  and 
untarnished. 

[174.]  Mix  two  ounces  of  red-lead  with  about  two  drams 
of  pulverized  charcoal,  one  ounce  of  common  salt,  and  a 
little  borax  (685,  691);  heat  the  mixture  in  a  Hessian  cru- 
cible (643,  670)  in  the  crucible  furnace  (158),  that  the  lead 
may  be  reduced.  If  the  experiment  be  properly  performed, 
metallic  lead,  equivalent  to  the  red-lead  used,  will  be  ob- 
tained at  the  bottom  of  the  crucible. 

[175.]  Pulverize  a  native  oxide  of  tin  (323),  mix  it  with 
one-eighth  its  weight  of  pulverized  charcoal  (332)  and  half 
its  weight  of  borax  (691),  put  the  mixture  into  a  crucible 
with  a  few  pieces  of  charcoal  over  it,  and  heat  it  (669,  .670) 
to  reduce  the  metal.  The  tin  will  ultimately  be  obtained  at 
the  bottom  of  the  crucible.  * »', 

[176.]  Melt  carbonate  of  soda  in  a  platinum  crucible 
(653,  662),  in  the  crucible  furnace  (158,  670).  Afterwards 
melt  green  glass  in  the  platinum  crucible  in  the  same  fur- 
nace (670). 

[177.]  Melt  borax  in  the  platinum  crucible  over  a  large 
spirit-lamp  (205,  666),  or  oil-lamp  (212,  66,7). 

[178.]  Mix  together  three  parts  by  weight  of  bi-carboriate 
of  potash,  and  one  part  of  pulverized  flints,  see  experiment 
168;  fuse  the  mixture  in  a  platinum  crucible  (653,  662),  by 
means  of  the  crucible  furnace  (670);  pour  out  the  result 
upon  a  clean  cold  stone  or  a  metallic  surface,  and  dissolve 
it  in  water. 

[179.]  Carefully  melt  a  mixture  of  caustic  alkali  and  sili- 
ceous matter  in  a  silver  crucible  (656),  using  the  crucible 
furnace  (158,  670). 

[ISO;]  Take  the  silver  obtained  by  reducing  the  chloride 
of exp. 104,  by  means  of  zinc  and  a  little  sulphuric  acid,  and 
fuse  it  in  a  Hessian  crucible  with  a  little  carbonated  alkali 
(686). 


CRUCIBLE  OPERATIONS.  645 

[181.]  Mix  an  ounce  of  oxide  of  copper  with  one-twelfth 
its  weight  of  pulverized  charcoal  (332,  696).,  adding  oil 
enough  to  make  the  whole  into  a  paste  (697);  put  it  into  a 
crucible  with  an  ounce  of  borax,  and  ignite  it  in  «a  wind- 
furnace  (669),  or  a  crucible  furnace  if  it  can  be  made  to 
afford  sufficient  heat  (168,  670).  The  oxide  will  be  reduced, 
and  a  button  of  metallic  copper  obtained. 
•  [182.]  Line  a  crucible  with  charcoal  (652);  place  some 
oxide  of  copper  in  it  (696);  then  add  more  charcoal,  and 
close  it  with  a  cover  nearly  tight* (676).  Apply  a  tempera- 
ture sufficient  to  melt  copper  for  half  an  hour ;  the  metal 
will  be  reduced.  If  the  heat  has  not  been  quite  sufficient 
to  melt  the  copper,  still  it  will  be  found  perfectly  reduced 
and  adhering  together  in  one  mass/-  ." 

[JL83.]  Introduce  some  dry  pulverized  (323)  oxide  of  iron, 
as,  for  instance,  clean  scales,  into  a  crucible  lined  in  a  similar 
manner  (652);  cover  and  heat  it  for  an  hour  at  a  high  tem- 
perature (673);  the  oxide  will  be  reduced  throughout,  and 
leave  the  iron  in  a  spongy  and  extremely  divided  state.* 
If  a  portion  of  this  iron  be  cut  off  in  thin  layers  by  a  knife, 
heaped  up  and  lighted  at  one  corner,  it  will  burn  like  tinder. 

[184.]  Put  some  sulphate  of  potash  into  a  similar  crucible 
(652);  place  some  charcoal  over  it,. and  then  lute  on  a  cover 
(676);  heat  the  crucible  highly  for  an  hour,  after  which  take 
it  out  of  the  furnace  and  allow  it  to  cool;  when  cold,  the 
sulphate  will  be  found  converted  into  a  pure  sulphuret  of 
potassium. f 

[185.]  Take  the  oxide  of  iron  separated  in  experiment 
106,  and  when  washed,  and  also  dried  as  much  as  possible 
by  the  heat  of  the  bath  or  a  hot  plate  .(171,  609),  introduce 
it  into  a  platinum  crucible  (653),  and  raise  the  temperature 
to  dull  redness  over  the  chemical  or  spirit-lamp  (666)  to 
dissipate  the  last  portions  of  water.  If  the  crucible  be  large, 
or  the  lamp  alone  ineffectual,  use  the  jacket  (667)  for  the 
purpose  of  increasing  the  power. 

[186.]  Put  50  grains  of  dry  hydrate  of  lime  into  a  coun- 
terpoised platinum  crucible  (653,  682);  carefully  heat  the 

• 

*  Berthier,  Annales  de  Chimie,  xxvii.  24.        j  Journal  des  Mines,  vii.  421, 


646  FURNACE  TUBE  OPERATIONS. 

crucible  and  its  contents  to  redness  for  a  quarter  of  an  hour 
(667);  then  weigh  and  ascertain  the  loss  (51,682):  again  heat 
for  five  minutes,  to  ascertain  whether  any  further  loss  will 
be  occasioned  (58,  59,  682).  In  this  manner  the  water  may 
be  driven  off,  and  the  composition  of  the  hydrate  of  lime 
ascertained.  The  loss  should  be  12.16  grains. 

XIV.  Furnace  Tube  Operations. 

[187.]  Send  steam  (706, 704)  through  an  iron  tube  (700) 
containing  iron  turnings  (721),  heated  to  redness  (699)  in  a 
furnace.  The  water  will  be  decomposed,  and  a  mixture  of 
hydrogen  gas  and  steam  evolved,  or  even  gas  alone  if  the 
operation  be  slow  ;  this  may  be  burnt  at  the  end  of  the  tube, 
or  received  in  jars  over  a  pneumatic  trough  (704,  746). 

[188.]  Decompose  ammonia  by  passing  it  through  a  red- 
hot  iron  tube  (7J9,  700).  The  ammonia  may  be  liberated 
from  a  retort  containing  the  usual  mixture  of  quick  lime  and 
sal  ammoniac ;  and  the  gases  evolved  may  be  received  into 
jars  (748,  751)  over  the  pneumatic  trough.  The  ammonia 
will  in  this  manner  be  resolved  into  a  mixture  of  three  parts 
by  volume  of  hydrogen,  and  one  part  of  nitrogen,  which  upon 
trial  will  be  found  to  be  combustible. 

[189.]  Pass  ammonia  in  the  same  manner  over  black  oxide 
of  manganese  (724)  heated  to  redness  in  a  tube  either  of  iron 
(700),  glass,  or  earthenware  (703).  The  vapours,  if  thrown 
into  a  globe  or  large  flask,  will  be  found  to  produce  red 
fumes,  from  the  presence  of  nitrous  acid ;  the  alkali  being 
decomposed  in  this  experiment  and  occasioning  the  produc- 
tion of  an  acid  body. 

[190.]  Pass  oil  through  an  iron  tube  heated  to  redness 
(700, 708)  in  a  furnace.  The  fluid  will  be  decomposed,  and 
a  quantity  of  oil  gas  produced  which  will  burn  at  the  farther 
end  of  the  tube  with  a  brilliant  flame,  or  may  be  received 
and  preserved  in  jars  (746)  over  water. 

[191.]  Decompose  alcohol  (706)  by  passing  its  vapour 
gradually  through  a  glass  tube  (703)  containing  rock  crystals 
(718),  heated  by  the  lamp  (710);  collect  the  gas  (746),  and 
observe  its  combustibility  and  other  properties.  Ether  may 
be  decomposed  in  the  same  manner :  the  deposition  of  car- 


FURNACE  TUBE  OPERATIONS.  647 

bon  will  be  far  more  abundant  than  when  alcohol  is  em- 
ployed. » 

[192.]  When  chlorine  is  passed  over  crystals  of  metallic 
titanium  in  a  glass  tube  heated  by  the  lamp  (710)  combina- 
tion takes  place,  and  a  chloride  of  titanium  is  deposited  in 
the  cool  part  of  the  tube  (727).* 

[193.]  In  the  same  manner  chlorine  passed  over  arsenical 
ores  combines  with  the  arsenic,  sulphur,  and  other  substances 
present,  and  carries  them  onwards  (727).  For  a  complicated 
but  excellent  process  of  this  kind,  see  Berzelius,  on  the  Ana- 
lysis of  Arsenical  Ore.f 

[194.]  Put  peroxide  of  manganese  into  a  green  glass  tube 
(703),  apply  heat  by  means  of  Cooper's  lamp  (710),  and  then 
pass  hydrogen  over  it  (724).  The  peroxide  will  become 
protoxide,  and  the  manner  in  which  the  change  proceeds 
will  be  observed  through  the  glass. 

[195.]  Send  naphthaline  (698)  through  a  tube  heated  to 
redness  by  the  ordinary  oil-lamp  (709),  that  the  effect  of 
heat  upon  the  substance  may  be  observed. 

[196.]  Select  a  green  glass  tube  about  one-third  of  an 
inch  in  diameter  (703),  and  counterpoise  it  (65).  Introduce 
some  pure  baryta  in  fragments,  so  as  loosely  to  occupy  the 
length  of  six  inches  (718,  725);  weigh  it,  and  ascertain  the 
quantity  of  earth  introduced  (52).  Then  heat  the  tube  and 
its  contents  to  dull  redness,  either  by  Cooper's  lamp-furnace 
(710),  or  any  other  convenient  means  (707),  and  pass  oxygen 
(704)  over  the  earth,  until,  from  the  abundance  which  issues 
at  the  open  extremity  of  the  tube  (725), 'it  is  evident  that  no 
more  will  be  absorbed.  Allow  the  tube  to  cool  (58),  closing 
the  extremities  (960,  1253)  to  prevent  the  free  access  of  air. 
Then  weigh  it  again  (59),  and  ascertain  how  much  oxygen 
has  been  absorbed  to  convert  the  baryta  introduced  into 
peroxide  of  barium. 

[197.]  Make  a  similar  experiment  with  lime,  except  that 
instead  of  oxygen,  pass  chlorine  over  the  earth  (727).  It 
will  be  found,  if  the  gases  be  collected  (746),  that  oxygen  is 

*  Mr  Georges.    Annales  of  Philosophy,  N.  S. 
t  Annales  de  Chimie,  xvii.  p.  113. 


648  PNEUMATIC    MANIPULATION. 

evolved  during  the  experiment,  the  lime  being  decomposed, 
and  its  metallic  base,  calcium,  combined  with  the  chlorine 
to  form  a  chloride.  The  quantity  of  oxygen  set  free  may  be 
ascertained  by  collecting  all  the  gas  (750),  and  absorbing  the 
excess  of  chlorine.  The  quantity  of  lime  experimented  with 
may  be  ascertained  also,  as  well  as  the  quantity  of  chloride 
of  calcium  produced  (65,  59),  and  in  this  manner  the  com- 
position of  the  oxide  and  ,the  chloride  of  calcium  may  be 
ascertained,  not  only  as  to  the  elements  they  contain,  but  as 
to  their  actual  quantities. 

[198.]  By  putting  some  spongy  platinum  into  a  glass  tube 
(703),  and  heating  it  over  an  oil  (212,  709)  or  spirit-lamp 
(205),  and  then  passing  mixtures  of  gases  through  the  tube, 
the  power  of  the  platinum  (720)  to  facilitate  chemical  changes 
may  be  easily  observed.  Thus  a  mixture  of  carbonic  oxide 
and  oxygen  is  readily  converted  into  carbonic  acid  at  com- 
paratively low  temperatures  and  without  explosion. 

* »         •      •  *  *    *  *  *  * 

XV.  Pneumatic  Manipulation. 

[199.]  Put  about  one  ounce  of  granulated  zinc  (351)  into 
a  pint  retort  (428,  435);  dilute  half  an  ounce  (118)  by  mea- 
sure of  oil  of  vitriol,  with  four  or  five  measured  ounces  of 
water,  add  the  mixture  to  the  zinc  in  the  retort  (436),  and 
collect  the  gas  evolved  (746)  in  jars  (739),  over  the  pneu- 
matic water  trough  (729).  When  two  or  three  jars  of  gas 
(751)  have  been  received,  remove  the  retort,  and  proceed  to 
manipulate  with  the  gas.  Transfer  (759)  a  portion  from  one 
of  the  jars  into  a  lipped  glass  (368,  760),  then  transfer  a  little 
from  the  glass  (761,  765)  into  a  tube  (743),  using  a  funnel 
(766)  for  the  purpose,  and  filling  the  tube  for  about  two 
inches  in  length  with  gas;  close  the  end  of  the  tube  by  the 
finger  (766),  and  then  apply  a  lighted  taper  to  the  gas  (950) 
to  prove  its  combustible  nature.  Refil  the  tube  with  water 
(762),  and  transfer  a  second  portion  of  gas  into  it  from  the 
glass  (765),  not  using  the  funnel  but  the  fingers  only  (763). 
Transfer  a  part  of  the  gas  from  this  tube  to  a  smaller  (764), 
not  using  a  funnel  but  the  fingers,  as  already  directed. 

[200.]  Fill  a  transfer  jar  (742)  with  water  (755)  over  the 
trough,  and  decant  some  of  the  hydrogen  gas  from  the  jars 


PNEUMATIC  MANIPULATION.  649 

into  it  (759);  depress  the  transfer  jar  in  the  water  of  the 
trough  (755),  so  as  to  cause  a  jet  of  gas  to  issue  at  the  aper- 
ture of  the  stop-cock  (827)  as  soon  as  the  latter  is  opened ; 
do  this  gradually,  and  apply  a  light  to  the  issuing  jet  of 
hydrogen,  so  as  to  inflame  it,  and  show  its  combustibility. 

[201.]  Fill  a  small  jar  or  a  large  glass  (368)  with  water  at 
the  trough  (751)  and  throw  part  of  the  remaining  hydrogen 
gas  into  it  (759),  until  the  jar  or  glass  is  full.  Raise  it 
carefully  from  the  water  into  the  air,  still  keeping  the  mouth 
horizontal  and  downwards.  It  will  be  found  that  after  the 
lapse  of  a  minute  nearly,  still  a  light  applied  to  the  air  in 
the  glass  will  cause  slight  explosion,  from  the  ignition  of  the 
hydrogen  gas  remaining  in  it.  Refil  the  jar  or  glass  in  the 
trough  with  hydrogen  (759),  cover  its  mouth  with  a  glass 
plate  (739,  1348),  set  the  glass  upright,  mouth  upwards,  and 
then  remove  the  plate.  If,  after  the  lapse  of  two  or  three 
seconds  only,  a  light  be  applied  to  the  contents  of  the  glass, 
no  inflammation  will  take  place,  the  hydrogen  gas  having 
now  escaped,  in  consequence  of  its  lightness,  and  the  posi- 
tion of  the  vessel. 

[202.]  Put  some  fragments  of  marble  (315)  into  a  gas  bot- 
tle (746),  and  pour  upon  them  muriatic  acid,  diluted  with  thrice 
its  bulk  of  water;  carbonic  acid  gas  will  be  evolved,  which 
is  to  be  received  in  jars  (739)  over  the  water  trough  (729). 
Transfer  a  portion  of  it  (760)  into  a  small  jar  (739),  filling 
the  latter  and  then  closing  its  mouth  with  a  glass  plate  (754, 
1348);  take  it  out  of  the  trough  and  set  it  upright,  with  the 
mouth  upwards.  Remove  the  plate  and  apply  a  lighted  taper 
to  the  gas ;  the  taper  will  be  extinguished  as  jsoon  as  it  de- 
scends in  the  jar  below  the  level  of  the  edge.  Leave  the 
jar  thus  open  for  a  minute  or  two,  the  air  about  it  being 
undisturbed,  and  then  on  applying  the  taper,  it  .will  be  ob- 
served to  be  extinguished  as  readily  as  before.  Such  is  the 
weight  of  this  gas,  that  after  four  or  five  minutes,  still  enough 
will  be  left  in  the  jar  to  extinguish  the  taper. 

[203.]  Refil  the  jar  with  carbonic  acid  gas  over  the  trough 
from  the  portion  originally  received  (751,  759);  put  a  lighted 
taper  fastened  to  a  wire  at  the  bottom  of  a  similar  jar  stand- 
ing on  the  table  and  containing  air;  it  will  burn  freely;  bring 
4G 


650  PiNEUMATlC  MANIPULATION. 

the  mouth  of  the  jar  containing  the  carbonic  acid  gas  to  the 
mouth  of  that  inclosing  the  taper,  and  pour  the  carbonic  acid 
gas  into  the  latter  jar;  the  gas  will  descend  and  extinguish  the 
flame  as  effectually  as  so  much  water.  Remove  the  taper 
and  test  the  presence  of  the  gas  by  another  method,  namely, 
by  lime  water,  for  which  purpose  pour  a  little  lime  water 
into  the  jar  and  agitate  it,  it  will  immediately  become  turbid 
from  the  formation  of  carbonate  of  lime.  In  doing  this,  do 
not  bring  the  mouth  of  the  lime  water  bottle  near  the  jar 
containing  the  carbonic  acid,  but  pour  the  lime  water  re- 
quired into  a  glass,  and  from  that  into  the  jar;  otherwise  all 
the  lime  water  in  the  bottle  will  become  turbid,  from  a  little 
carbonic  acid  gas  thus  introduced. 

[204.]  Transfer  a  portion  of  carbonic  acid  gas  at  the  water 
trough  into  a  tube  (762),  of  a  size  that  may  be  closed  by 
the  finger  (766),  then  quickly  introduce  a  piece  of  potassa 
through  the  water  into  the  tube;  close  the  tube  by  the  finger, 
and  shake  it  to  dissolve  the  potassa ;  then  open  its  aperture 
by  removing  the  finger  under  water,  observe  the  absorption 
of  the  gas  by  the  alkaline  solution ;  the  whole  of  the  carbonic 
acid  gas  will  be  absorbed,  and  thus  its  purity  may  be  ascer- 
tained. 

[205.]  Mix  one  volume  of  good  alcohol  with  two  volumes 
of  oil  of  vitriol  carefully  (436),  because  of  the  heat  liberated. 
Distil  the  mixture  in  a  glass  retort  (386),  applying  the  heat 
of  an  oil  lamp  (212,  386),  and  receive  the  gas  into  jars  over 
water  (751);  it  will  be  olefiant  gas,  and  should  burn  with  a 
brilliant  flame.  Receive  small  portions  into  tubes  (743),  and 
observe  whether  it  burns  with  a  bright  flame  when  lighted 
(950,  749);  do  not  collect  the  gas  to  be  preserved  until  that 
be  the  case.  During  the  progress  of  the  operation,  test  the 
gas  that  is  passing  over  in  the  same  manner,  and  when  its 
flame  decreases  in  brightness,  preserve  that  which  is  after- 
wards collected  apart,  as  inferior  and  impure.  Allow  the  gas 
to  stand  over  water  (751,  753),  or  agitate  it  with  water  to 
wash  out  the  sulphurous  acid.  Transfer  a  jar  filled  with  it 
into  an  evaporating  basin  (753),  and  add  some  quick-lime  to 
the  water  in  which  it  stands,  for  the  purpose  of  more  effectu- 
ally separating  the  carbonic  and  sulphurous  acid  gases. 


PNEUMATIC    MANIPULATION.  651 

206.]  Half  fill  a  tall  cylindrical  jar  (739)  with  chlorine 
(732)  over  the  pneumatic  trough  (751),  and  then  throw  up 
an  equal  volume  of  the  olefiant  gas.  Immediately  transfer  the 
jar  into  a  large  basin  (.369,  753),  and  observe  the  gradual 
combination  and  disappearance  of  the  gaseous  fluids,  and  the 
production  of  a  liquid  in  drops,  insoluble  in  water,  and  so 
heavy  as  to  fall  through  it;  the  liquid  will  communicate  a 
very  aromatic  sweet  taste  to  it,  and  is  itself  powerfully  sweet 
and  sapid.  Into  a  similar  jar  (739)  throw  chlorine,  until  it 
be  two-thirds  full,  and  fill  the  remaining  third  with  olefiant 
gas.  Close  the  mouth  of  the  jar  with  a  glass  plate  (1348), 
remove  it  from  the  trough,  invert  it  two  or  three  times  (857), 
to  mix  the  contents,  and,  removing  the  plate,  immediately 
apply  a  light  to  the  mouth  of  the  vessel;  the  gases  will  com- 
bine with  inflammation,  the  flame  slowly  passing  through  the 
jar,  and  rendering  it  opaque  from  the  great  quantity  of  carbon 
suddenly  evolved. 

[207.]  Burn  a  jet  of  olefiant  gas  from  the  stop-cock  of  a 
transfer  jar  (742,  755)  in  the  manner  described  in  experiment 
200,  and  remark  the  brilliancy  and  beauty  of  the  flame.  Pass 
a  bladder  full  of  it  (820)  through  a  heated  glass  tube,  as  in 
the  practices  of  Section  XIV.  and  observe  both  the  deposition 
of  carbon  in  the  tube  (723),  and  the  diminished  intensity  of 
the  flame  produced  by  the  gas,  after  the  operation. 

[208.]  Put  some  fragments  of  sal  ammoniac  into  a  small 
dry  gas  bottle  (746),  retort  (429),  or  flask  (372,  746),  and 
add  strong  sulphuric  acid  ;  muriatic  acid  gas  will  be  evolved. 
Receive  it  into  jars  (739,  783),  over,  the  mercurial  trough 
(736,  782),  applying  the  heat  of  a  spirit-lamp  to  the  retort 
if  necessary  (199,  439),  and  shaking  the  vessel  to  break  the 
bubbles.  When  several  jars  are  filled  with  the  gas,  close  the 
mouth  of  one  of  them  by  a  plate,  and  place  it  upright  with 
the  mouth  upwards,  on  the  table  (739,  783).  Remove  the 
disc,  and  observe  the  fumes  produced  by  the  gas  in  the  air, 
and  the  heat  which  becomes  sensible  when  the  finger  is  dip- 
ped into  the  gas.  Apply  a  lighted  taper,  and  observe  its 
instant  extinction.  Pour  a  little  water  into  the  jar,  remark  the 
increase  of  fumes  within,  and  by  a  little  agitation  their  final 
absorption.  Test  the  acidity  of  the  solution  by  litmus  paper 


652  PNEUMATIC    MANIPULATION. 

(624,  617)  or  cabbage  liquor  (616),  and  test  the  acidity  of 
the  fumes  also  by  litmus  paper  (626). 

[209.]  Transfer  a  little  tube  full  of  water  into  another  jar 
of  the  gas  as  it  stands  over  the  mercury  (782);  observe  the 
immediate  absorption,  and  ultimately  the  entire  disappear- 
ance of  the  gas.  Remove  the  jar  from  the  trough  by  means 
of  a  flat  plate  (739,  783),  and  examine  the  solution  (624, 
&c.);  it  will  be  found  to  be  the  same  substance  as  ordinary 
solution  of  muriatic  acid. 

[210.]  Transfer  a  portion  of  the  muriatic  acid  gas  into  a 
tube  (743)  under  the  mercury  (787,  794),  then  close  the 
mouth  of  the  tube  by  the  finger  (766),  transfer  it  into  an 
evaporating  basin  containing  water  (732),  remove  the  finger, 
and  observe  how  instantaneously  the  gas  is  absorbed  by  the 
water.  * 

[211.]  Make  a  mixture  to  evolve  ammonia,  as  in  experi- 
ment 56.  Put  it  into  a  small  retort  (429,  438);  heat  it  by 
the  large  spirit-lamp  (205),  and  receive  the  ammoniacal  gas 
which  will  be  liberated  into  jars  (739)  over  the  mercurial 
trough  (736).  Throw  up  a  little  water  into  a  jar  of  the  gas, 
and  observe  its  solubility,  and  the  alkaline  nature  (624)  of  the 
solution  produced.  Take  two  jars,  one  containing  ammoniacal 
gas,  and  the  other  muriatic  acid  gas  of  the  last  experiment, 
observe  their  volumes  in  the  jars  (798),  and  then  pass  up  the 
ammoniacal  gas  gradually  into  the  muriatic  acid  gas  (787); 
dense  fumes  will  be  produced,  and  condensation  will  take 
place.  By  degrees  the  whole  of  one  of  the  gases  will  disap- 
pear with  an  equal  volume  of  the  other,  and  in  their  places 
will  remain  a  solid  muriate  of  ammonia.  Estimate  the  quan- 
tities of  the  two  gases  used  (798),  and  practically  verify  the 

*  Fill  with  hydrochloric  acid  gas,  a  tube  standing  over  a  cup  of  mercury ;  pour 
some  litmus  water  into  the  cup,  and,  gradually  raising  the  tube  out  of  the  mer- 
cury, suffer  the  mouth  of  it  to  reach  the  stratum  of  water.  The  instantaneous 
rush  of  the  coloured  test  into  the  tube,  and  its  as  immediate  change  of  hue,  will 
signally  demonstrate  the  great  absorbability  as  well  as  the  acid  character  of  the 
gas. 

By  transferring  a  tall  jar  of  this  gas  to  a  ground  glass  plate,  through  the  axis  of 
which  passes  a  pipe,  and  plunging  the  lower  end  of  the  pipe  into  water  coloured 
with  litmus,  the  student  will  make  a  beautiful  jet  of  differently  coloured  liquid, 
and  demonstrate  the  existence  of  the  vacuum  formed  by  absorption.— ED. 


PNEUMATIC  MANIPULATION.  653 

statement  just  made,  that  equal  volumes  of  the  two  condense 
each  other. 

[212.]  Make  muriatic  acid  gas  (826)  and  ammoniacal  gas 
(825),  and  receive  them  in  clean  dry  bottles  (824)  without 
the  aid  of  a  mercurial  trough. 

[213.]  Make  chlorine  in  a  glass  retort  (428),  from  a  mix- 
ture of  eight  parts  of  salt  with  three  parts  of  black  oxide  of 
manganese,  to  which  have  been  added  six  parts  of  sulphuric 
acid,  diluted  with  four  times  its  bulk  of  water,  and  allowed  to 
become  cold.  Heat  the  retort  gradually  by  an  oil-lamp  (212), 
removing  the  lamp  if  the  evolution  of  gas  become  quick,  or 
the  mixture  froths  over  into  the  neck  of  the  retort.  Receive 
the  gas  when  good  into  stoppered  bottles  (824),  in  a  trough 
containing  warm  water  (732);  close  the  bottles  well  (824), 
and  preserve  them  inverted  in  a  dark  place,  with  their  stop- 
pers and  necks  immersed  in  water.  To  test  the  goodness  of 
the  chlorine,  fill  a  tube  with  water,  and  receive  a  few  bub- 
bles of  the  gas  into  it,  then  remove  the  tube  to  a  trough  con- 
taining cold  water,  agitate  it  with  the  gas  (766),  and  observe 
whether  the  absorption  be  entire;  any  residue  is  impurity. 
This  trial  should  be  repeated  until  not  more  than  a  fourteenth 
part  remains  unabsorbed,  and  then  the  chlorine  may  be  re- 
ceived. 

[214.]  Make  an  aqueous  solution  of  the  gas  contained  in 
one  of  these  bottles  (824,  856).  Then  remark  its  bleaching 
powers,  as  shown  upon  a  little  finely-divided  indigo,  or  upon 
writing,  or  printed  calicoes,  &.G.* 

[215.]  Make  some  carbonic  oxide,  as  in  experiment  90; 
receive  it  into  jars  over  water  (748,  758).  Wash  it  well  over 
water,  or  lime  and  water,  as  in  experiment  205  with  olefiant 
gas,  or  even  over  alkaline  solutions.  Mix  (759,  857)  a  por- 
tion of  the  pure  gas  with  half  its  volume  of  oxygen  in  a  glass 
(368,  505);  transfer  a  little  of  the  mixture  into  a  tube  (761), 
and  applying  a  taper  to  it,  examine  its  combustibility;  it  will 
be  found  to  explode.  Transfer  a  small  quantity  of  the  mix- 
ture into  a  detonating  tube  (994),  pass  the  electric  spark 

*  Observe  the  heat  which  chlorine  communicates  to  the  finger,  while  the 
thermometer  is  unaffected  (Hare).— ED. 


654  PNEUMATIC  MANIPULATION. 

through  it  (986,  993);  explosion  will  take  place,  and  the 
bulk  of  the  gas  will  be  diminished.  By  agitation  the  re- 
maining gas  will  now  be  absorbed  5  or  if  a  little  piece  of 
potassa  be  introduced  and  agitated  with  it,  the  effect  will 
proceed  more  rapidly,  the  resulting  gas  being  carbonic  acid. 

[216.]  Transfer  a  portion  of  the  detonating  mixture  into 
a  dry  tubej  over  mercury  (792,  794),  and  from  that  transfer  a 
small  quantity  into  a  dry  eudiometer  tube,  also  over  mercury 
(994).  Observe  the  volume  of  gas  to  be  detonated  (798), 
and  when  the  explosion  has  taken  place  (997),  again  remark 
the  volume;  the  diminution  will  be  found  equal  to  one-third 
of  the  original  bulk.  Throw  up  a  lube  full  of  lime-water 
into  the  eudiometer :  the  opacity  thereby  occasioned,  and 
the  condensation  of  the  gas,  will  sufficiently  prove  that  car- 
bonic acid  gas  has  been  the  result. 

[217.]  Make  a  little  oxygen  in  a  tube  retort  (924)  from 
chlorate  of  potassa,  by  the  heat  of  a  large  spirit-lamp  (205), 
and  receive  the  gas  in  tubes  (127)  and -phials  over  water, 
contained  in  an  evaporating  basin  (946).  Try  portions  of 
this  oxygen  in  the  tubes  (766).  Introduce  a  glowing  taper, 
or  the  ignited  end  of  a  splinter  of  wood,  into  a  tube  contain- 
ing some  of  it,  and  observe  the  increased  combustion  at  the 
moment.  Twist  together  five  or  six  folds  of  steel  harpsichord 
wire,  fasten  a  little  piece  of  wood  to  one  end  of  the  bundle, 
light  it  and  then  plunge  it  into  the  oxygen  gas  contained  in 
one  of  the  phials.  The  steel  wire  will  burn  brilliantly.* 

[218.]  Transfer  a  little  of  the  oxygen  of  the  preceding 
experiment  into  a  dry  tube  (792,  793)  over  mercury,  or  make 
a  little  oxygen  from  the  tube  retort  (924)  directly  into  dry 
tubes  or  jars  over  the  mercurial  trough  (737).  Mix  a  por- 
tion of  it  with  twice  its  volume  of  dry  hydrogen,  transfer  a 
part  of  the  mixture  into  a  dry  eudiometer  tube  (994),  using 
Pepys'sf  instrument  for  the  purpose  (794),  and  detonate  it 
by  the  electric  spark  (986).  If  pure,  the  gases  will  entirely 
disappear,  and  only  a  minute  quantity  of  water  will  remain. 

[219.]  Make  some  nitric  oxide  gas  in  a  glass  retort,  by 

*  Nitrated  paper  answers  best  for  kindling.— ED. 
f  Or  rather  Dr  Hare's. — ED. 


PNEUMATIC  MANIPULATION.  655 

acting  on  copper  clippings,  with  a  mixture  of  two  parts  water 
and  one  part  nitric  acid.  The  action,  which  is  often  tardy 
at  first,  very  frequently  increases  on  a  sudden  and  becomes 
powerful ;  hence  attention  and  watchfulness  are  required. 
The  gas  should  be  received  into  glasses  (743)  or  jars  (739) 
over  water,  and  after  standing  an  hour  or  two,  will  be  suffi- 
ciently washed  from  acid  fumes.  Mix  a  portion  of  this  gas 
in  a  glass  (743,  759),  with  some  of  the  oxygen  of  experiment 
217.  Observe  the  deep  orange  colour  produced,  and  the 
rapid  disappearance  of  the  gases  in  consequence  of  the  solu- 
bility of  the  product  in  the  water. 

[220.]  Measure  equal  volumes  of  common  air  and  nitric 
oxide  (776),  mix  them  together  in  a  tube  (127)  over  water, 
and  observe  the  diminution  (780). 

[221.]  Mix  equal  volumes  of  dry  air  and  hydrogen  over 
mercury  (798),  introduce  a  portion  of  the  mixture  into  a  tube, 
and  observe  its  detonation  by  the  application  of  a  lighted 
taper.  Introduce  a  portion  of  the  mixture  into  an  eudiome- 
ter tube  (994),  observe  its  volume  accurately  (800),  detonate 
it  by  the  electric  spark  (994),  and  then  remark  the  diminu- 
tion in  bulk  (800).  One  third  of  the  diminution  will  be  the 
quantity  of  oxygen  existing  in  the  common  air  used,  the  latter 
amounting  to  half  the  bulk  of  the  mixture  detonated.* 

[222.]  Take  any  one  of  the  jars  of  the  preceding  experi- 
ments containing  gas  standing  over  water,  and  measure  the 
gas  in  it  (772).  In  doing  this  be  careful  to  level  the  surfaces 
accurately  (769),  to  mark  the  place  of  the  gas  before  trans- 
ferring it  (767),  and  to  verify  the  measurement  (770)  in  the 
manner  described.  Note  also  the  temperature  and  pressure 
(780,  773).  Then  measure  a  given  quantity  of  gas  into  a 
graduated  jar,  or  up  to  a  certain  mark  in  a  jar  (774),  adjust- 
ing the  quantity  accurately  (775.)  Measure  out  also  a  given 
number  of  parts  into  a  graduated  tube  (127),  as  eight  or  ten 
(779);  carefully  adjusting  the  quantity  by  the  use  of  the 
finger  (7.75).  Make  use  of  a  standard  measure  (776)  in 
mixing  together  two  parts  of  hydrogen  with  one  of  oxygen 
by  volume,  for  experiments  like  those  of  221. 

*  Make  the  experimental  investigation  of  the  quantity  of  oxygen  in  the  air, 
using  Hare's  sliding-rod  eudiometer. — ED. 


656  PNEUMATIC  MANIPULATION. 

[223.]  Transfer  the  remaining  oxygen,  chlorine,  hydrogen, 
or  any  other  valuable  gas  of  the  preceding  experiments  that 
may  be  unused,  into  bottles  (760),  being  careful  to  close 
their  mouths  accurately  with  stoppers  (824). 

[224.]  Measure  half  a  cubical  inch,  or  any  small  quantity 
of  oxygen,  hydrogen,  or  common  air,  in  a  tube  (127)  over 
mercury  (798);  then  transfer  the  tube  to  a  basin  of  water 
(766),  allow  the  mercury  to  escape,  and  again  observe  the 
volume  of  gas  now  that  it  stands  over  water  (769),  the  level 
being  in  both  cases  attended  to  (767).  In  this  way  the 
effect  produced  by  the  different  curvatures  of  mercury  and 
water  in  the  tube  (135)  may  be  valued  and  appreciated. 

[225.]  Cement  a  cap  tightly  (833)  upon  the  mouth  of  a 
clean  dry  retort  (429),  attach  a  stop  cock  (827),  and  by  an 
air-pump  (838,  858)  or  syringe  (861)  examine  whether  the 
arrangement  be  air-tight.  Exhaust  the  retort  (858,  866), 
attach  it  to  a  graduated  transferring  jar  (742,  836),  contain- 
ing common  air,  and  allowing  the  air  to  enter  (869),  observe 
how  much  is  required  to  fill  the  retort.  Exhaust  the  retort 
again  (858),  and  attaching  it  to  a  graduated  transfer  jar  (742) 
containing  nitric  oxide  (experiment  219),  allow  so  much  to 
enter  (869)  as  is  equal  to  two-thirds  of  its  capacity;  then 
remove  and  attach  it  to  another  graduated  transfer  jar  (742), 
containing  oxygen,  open  the  stop-cock,  and  allow  so  much 
to  enter  (869)  as  is  equivalent  to  one-third  in  bulk  of  the 
contents  of  the  retort :  then  close  the  stop-cock.  The  two 
gases  will  combine,  and  form  a  deep  red  gaseous  product, 
which  is  nitrous  acid,  but  great  condensation  will  at  the 
same  time  occur.  To  measure  the  extent  to  which  this  pro- 
ceeds, allow  the  vessel  to  cool,  that  the  heat  evolved  may 
not  tend  to  expand  the  gases,  and  then  attach  it  to  a  gra- 
duated transfer  jar  (742),  containing  hydrogen  or  nitrogen, 
or  some  gas  dissimilar  to  those  which  have  been  used.  Open 
the  communication  (869),  and  observe  how  much  gas  will 
enter  to  fill  the  retort,  at  a  pressure  equal  to  that  of  the 
atmosphere  (767,  773).  This  quantity  will  be  nearly  one 
half  the  capacity  of  the  vessel.  Then,  upon  dipping  the 
stop-cock  into  water,  opening  it,  and  cooling  the  retort 
slightly  (447),  water  will  enter;  and  dissolving  the  red 


PNEUMATIC  MANIPULATION.  657 

gaseous  nitrous  acid,  will  show  by  the  quantity  of  unab- 
sorbed  air  or  gas  left,  how  much  pf  the  mixed  contents  of 
the  flask  were  soluble  in  that  fluid. 

[226.]  Fix  a  cap  and  stop-cock  upon  a  retort  as  before 
(833),  introduce  a  little  litharge,  and  exhaust  the  air  from 
the  vessel  (858).  Afterwards  fill  it  with  muriatic  acid  gas 
(869)  from  a  transfer  jar  over  mercury  (742,  782,  809);  leave 
the  communication  open,  and  heat  the  litharge  (866);  the 
latter  will  change  colour,  and  water  will  appear,  and  after 
some  time,  the  mercury  will  be  observed  to  rise  in  the  re- 
ceiver beneath,  to  a  considerable  degree,  partly  in  conse- 
quence of  the  actual  decomposition  of  a  portion  of  the  gas 
by  the  elements  of  the  oxide  of  lead,  with  the  consequent 
formation  of  water,  and  partly  of  the  absorption  of  gas  by 
the  water  so  produced. 

[227.]  Fill  a  transfer  jar  (742)  with  water,  over  the  trough, 
by  the  mouth  (755.)  Put  some  copper  leaf  (352,  1351)  into 
a  capped  retort  (833,  866),  attach  a  stop-cock  to  it,  and 
exhaust  the  air  from  within  (869);  screw  the  retort  upon  the 
transfer  jar,  and  then  pass  chlorine  (759)  which. has  been 
stored  and  set  aside  in  bottles  (824),  into  the  latter,  in*  suffi- 
cient quantities  to  fill  the  retort.  Admit  the  chlorine  to  the 
metal  leaf  (871);  the  latter  will  instantly  inflame  and  become 
converted  into  a  metallic  chloride. 

[228.]  Partly  fill  a  gas-holder  (811)  with  oxygen  (748), 
or  in  the  absence  of  oxygen,  with  air.  Fill  a  transfer  jar  or  a 
glass  with  the  gas,  at.  the  trough  on  the  top  of  the  instrument 
(813).  Exhaust  a  flask  (868),  and  fill  it  from  the  gas-holder 
(869,  813).  Fill  a  bladder  with  the  gas  from  the  holder 
(813).  Attach  a  flexible  tube  (841),  and  a  blow-pipe  jet 
(219),  to  the  stop-cock  (815),  and  throw  a  stream  of  the  gas 
upon  burning  charcoal  (251).  If  the  gas  be  oxygen,  and 
the  metals  be  silver,  lead,  iron,  copper,  or  tin,  they  may 
easily  be  burned  in  this  manner  with  brilliant  phenomena. 
In  the  same  way  oxygen  may  be  sent  through  the  tube  in 
the  baryta  experiment  196;  caoutchouc  connecting  pieces 
(449)  being  used  at  the  different  junctions. 

Now  transfer  the  gas  in  the  bladder  (820)  into  the  gas- 
holder again  (814),  and  removing  the  transfer  jar  above 
4H 


658  TUBE  CHEMISTRY. 

mentioned  into  a  deep  trough  (753),  transfer  the  gas  in  it 
first  into  a  bladder,  and  then  back  into  the  gas-holder  (814). 

[229.]  Fill  a  gas-holder  with  coal  or  oil  gas,  see  experi- 
ment 190  (811),  and  then  screwing  on  a  jet  (815),  burn  it 
gradually,  as  in  the  applications  of  such  gases  to  artificial 
illumination. 

[230.]  Compress  the  oxygen  contained  in  the  air-holder 
(813,  815),  experiment  228,  into  a  caoutchouc  bottle  (822), 
by  means  of  a  syringe  (858).  Then  use  the  latter  with  a 
spirit-lamp  as  an  oxygen  blow-pipe  (252). 

[231.]  Send  muriatic  acid  gas,  or  ammoniacal  gas  through 
a  series  of  Woulfe's  bottles  containing  water  (844),  to  form 
a  solution  (856);  use  a  safety  tube  (847);  and  connect  the 
joints  where  necessary  by  caoutchouc  connecters  (451). 

[232.]  Weigh  a  portion  of  air,  of  carbonic  acid,  and  of  oxy- 
gen (887),  attending  to  the  points  particularized  (892,  &c). 

[233.]  Dry  carbonic  acid  gas  over  muriate  of  lime  (897) 
at  the  mercurial  trough. 

XVI.  Tube  Chemistry.. 

[234.]  Test  a  mineral  water  (506,  913),  or  a  solution,  as 
that  of  experiment  74,  in  tubes  (911),  standing  in  corks  (67) 
or  glasses  (368),  or  in  a  rack  (911).  Use  the  dropping  bot- 
tle (402)  and  glass  stirrers  (912). 

[235.]  Dissolve  a  small  silver  coin  in  nitric  acid  in  a  tube 
(915);  examine  a  part  of  the  solution  for  copper  in  another 
tube  (911);  precipitate  a  part  of  the  remaining  solution  in 
a  third  tube,  by  a  piece  of  copper  wire,  and  wash  (914),  and 
dry  the  silver  precipitated.  Then  precipitate  the  remainder 
of  the  solution  in  a  fourth  tube,  by  a  solution  of  common 
salt,  and  wash  the  precipitate  well  (912)  in  the  tube  itself. 

[236.]  Heat  a  little  pulverized  sulphuret  of  antimony  in 
muriatic  acid,  using  a  bent  tube  of  the  form  represented  .in 
Sect.  XVI.,  for  the  purpose  (922);  examine  the  gas  evolved 
at  the  mouth  of  the  tube  (954)  by  a  taper  flame,  by  acetate 
of  lead  on  a  strip  of  paper,  by  smell,  &c.  (950),  it  will  be 
found  to  be  sulphuretted  hydrogen.  Return  the  muriatic 
acid  which  will  distil  over  (922),  upon  the  sulphuret,  once 
or  twice  in  succession.  At  last  pour  the  solution  over  the 


TUBE  CHEMISTRY.  659 

sulphuret  forward  into  the  angle  (922),  and  ultimately  pour 
a  little  of  it  into  water,  examine  the  effect,  and  observe 
whether  a  white  precipitate  be  produced. 

[237.]  Distil  some  oil  of  turpentine  from  a  tube  retort 
(924)  into  a  tube  receiver  or  phial  (925),  or  use  the  open 
bent  tube  receiver,  described  (926),  cooling  the  angular  part 
by  water  (927)  or  ice  (454). 

[238.]  Distil  a  piece  of  wax  in  the  tube  figured  (928), 
cool  the  first  receiving  angle  (927),  and  collect  the  liquid 
products  there ;  at  the  same  time  immerse  the  open  extre- 
mity of  the  tube  in  water  in  a  basin  (928),  and  collect  the  gas 
evolved  in  tubes  (946).  Examine  it  as  to  inflammability,  &c. 

[239.]  Heat  some  copper  or  iron  pyrites  in  a  green  glass 
tube  (935)  to  redness.  Receive  the  sulphur  which  sublimes 
into  a  plain  or  a  bent  tube  (938).  Heat  a  portion  of  the 
same  pyrites  in  an  open  tube  (939),  and  observe  by  the 
smell  and  appearance  whether  sulphur  burns  off  or  not. 

[240.]  Sublime  a  small  quantity  of  crude  naphthaline  from 
a  plain  tube,  into  a  bent  tube  receiver  (938). 

[241.]  Put  a  minute  quantity  of  metallic  arsenic  into  a 
plain  tube  (935),  closed  at  one  end ;  sublime  it  to  different 
parts  of  the  tube  by  the  heat  of  a  spirit-lamp  (199),  and 
observe  the  metallic,  crystalline,  and  other  appearances  of 
the  film  of  sublimed  metal;  continue  this  sublimation  to  and 
fro  until  the  arsenic  has  become  oxidized,  and  then  remark 
the  crystalline  appearance,  transparency,  whiteness,  and 
volatility  of  the  new  substance  formed. 

[242.]  Put  a  small  piece  of  common  paper,  about  half  an 
inch  square,  into  a  tube  (910)  closed  at  one  end ;  warm  the 
part  inclosing  the  paper  (918),  keeping  the  other  part  cold 
(936),  and  observe  the  dew,  which  will  appear  on  the  cold 
part,  and  which  proves  the  presence  of  moisture  in  the  paper. 

[243.]  Repeat  experiment  39,  in  open  inclined  tubes  (939), 
for  the  purpose  of  observing  the  production  of  acid  and  alkali 
(624,  626)  at  the  upper  apertures. 

[244.]  Put  some  per-oxide  of  iron  into  a  tube  (910),  ex- 
amine it,  and  remark  that  it  is  not  magnetic  (1391);  add  a 
little  naphthaline,  and  heat  the  oxide  to  redness  in  its  (940) 


660  TUBE  CHEMIStRY. 

vapour;  after  a  short  time,  examine  it  again  by  the  magnetic 
needle  (1393),  when  it  will  be  found  highly  magnetic. 

[245.]  Evaporate  a  solution  containing  silver,  or  any  other 
requiring  the  dissipation  of  excess  of  acid  (592),  in  a  bent 
tube  evaporator  (943),  then  add  water,  and  apply  a  slight 
degree  of  heat  to  dissolve  all  that  is  soluble. 

[246.]  Make  a  little  oxygen  gas  in  a  tube  retort  (924) 
from  chlorate  of  potassa,  and  receive  it  in  tubes  (910)  im- 
mersed in  a  basin  of  water  (946).  Examine  the  gas  by  a 
splinter  of  wood,  with  a  spark  of  fire  at  the  extremity  (766); 
ascertain  how  small  a  bubble  of  oxygen  may  be  thus  tried 
with  readiness  and  certainty.  Make  a  little  hydrogen  into 
tubes  at  the  same  trough  (946),  and  try  in  a  similar  manner 
with  how  small  a  quantity  its  power  of  inflaming  may  be 
certainly  ascertained.  Theri  mix  two  volumes  of  the  hydro- 
gen with  one  volume  of  the  oxygen  (763),  and  remark  with 
how  minute  a  bubble  the  explosive  power  of  the  mixture 
may  be  observed  in  a  tube. 

[247.]  Make  a  little  muriatic  acid  gas  (736)  in  a  tube 
retort  (924),  and  receive  it  into  the  mercurial  receiver  de- 
scribed (950);  use  it  in  small  successive  portions  in  the  man- 
ner directed,  for  the  purpose  of  ascertaining  the  general  pro- 
perties of  the  gas. 

[248.}  Make  a  little  oxygen  in  the  bottom  of  a  tube  (954), 
and  try  its  powers  in  the  tube  itself.  Prepare  a  little  sul- 
phurous acid  gas  in  the  same  manner  (954),  and  observe  its 
powers  of  extinguishing  flame,  of  reddening  and  then  bleach- 
ing litmus  paper  (617),  its  odour,  &c.,  at  the  mouth  of  the 
tube.  Put  a  few  pieces  of  zinc,  and  a  little  muriatic  acid 
into  such  a  tube,  and  examine  the  gas  as  it  passes  off.  It 
will  prove  to  be  hydrogen. 

Prepare  euchlorine  also  in  the  bottoms  of  tubes,  and  repeat 
all  the  experiments  and  observations  with  it,  described  (955). 

[249.]  Decompose  oxalic  acid  by  sulphuric  acid  in  the 
bent  tube,  described  (958).  Test  the  combustibility  and 
other  properties  of  the  gas  evolved,  upon  successive  portions 
at  the  mouth  of  the  tube  (950).  The  gas  is  a  mixture  of 
carbonic  acid  and  carbonic  oxide. 

[250.]  Generate  muriatic  acid  gas  in  a  phial,  with  a  cork 


TUBE  CHEMISTRY.  661 

and  tube  (484),  pass  the  gas  over  water  in  a  tube,  Woulfe's 
apparatus  (959),  and  examine  the  solution  formed.  It  will 
be  found  to  be  powerfully  acid  (624),  precipitating  nitrate  of 
silver  (912),  dissolving  carbonate  of  lime  (915),  and  indeed 
being  a  pure  solution  of  muriatic  acid. 

[251.]  Condense  a  gas  into  a  liquid  in  the  manner  de- 
scribed p.  440,,&c.  Experiment  with  sulphurous  acid  gas 
(970),  or  cyanogen  (962),  as  being  those  substances  which 
incur  the  least  risk. 

[252.]  When  upon  any  occasion  a  comparatively  rare  fluid 
product,  as  chloride  of  phosphorus,  for  instance,  has  been 
obtained  in  a  pure  state,  confine  it  in  a  retaining  tube  (929). 
Observe  its  action  upon  water  or  upon  litmus  paper,  in  the 
air  (624),  dispensing  the  small  portions  necessary  from  the 
beak  of  the  tube',  then  sealing  up  the  remainder  (929).  Seal 
up  a  specimen  of  the  good  chloride  of  phosphorus  perma- 
nently (974,  1189)  for  preservation. 

[253.]  Decompose  a  certain  weight  (52)  of  chlorate  of 
potassa  in  a  green  glass  tube  (703,  910),  by  a  heat  (935) 
sufficient  to  drive  off  all  that  is  readily  volatile,  and  all  the 
oxygen.  Then  again  weigh  the  tube  and  its  contents  (59), 
and  ascertain  the  loss  of  weight.  This  will  be  the  weight 
of  the  oxygen  which  existed  in  the  salt  that  has  thus  been 
decomposed  and  analyzed.  The  residue  will  be  chloride  of 
potassium. 

[254.]  Put  tartrate  of  lead  into  a  green  glass  tube  (703, 
910),  contract  the  extremity,  but  do  not  close  it  (1184),  heat 
the  tartrate  gradually,  so  as  to  decompose  it  in  succession! 
beginning  at  the  end  nearest  the  aperture,  (710).  In  this 
way  dissipate  all  that  is  volatile.  A  black  powder  will  re- 
main, which  will  inflame  the  moment  it  is  poured  out  into 
the  air,  and  ourn  for  sorfle  lime.  By  sealing  up  the  con- 
tracted aperture  of  the  tube  whifet  if  is  still  hot  (1190),  the 
powder  may  be  preserved  for  any  period  of  time  without 
injury. 

[255.]  Heat  a  solution  to  212°  in  a  tube,  by  means  of  a 
water-bath  formed  by  another  tube  (259),  shorter  and  wider 
than  the  first. 


662  ELECTRICITY. 

[256.]  Freeze  a  little  water  in  a  tube  (910),  by  a  piece  of 
ice  and  some  salt  (454). 

XVII.  Electricity. 

[257.]  Excite  a  glass  rod  (1021)  by  silk,  with  a  little 
amalgam  spread  upon  it  (981).  Observe  its  effect  when 
brought  near  to  the  face,  or  its  power  over  an  electrometer 
(1012).  Excite  a  stick  of  wax  or  resin  (1021),  by  friction 
with  flannel  (1014),  and  remark  its  influence  upon  the  elec- 
trometer (1022,),  and  other  light  bodies. 

[258.]  Experiment  with  a  Bennet's  electrometer  (1012), 
first  diverging  the  leaves  by  brushing  the  cap  lightly  with 
warm  flannel,  and  then  determining  the  kind  of  electricity 
produced  (1021).  Diverge  the  leaves  by  the  rapid  evapora- 
tion of  water,  and  ascertain  the  kind  of  electricity  developed. 
Occasion  divergence  by  contact  of  gxcited  bodies  (1013, 
1020),  and  also  by  approximation  (1014,  1020);  and  in  each 
case  determine  the  kind  of  electricity  which  has  produced 
the  effect  (1021).  Insulate  the  substances  whose  electricity 
is  to  be  examined,  upon  stick-lac  or  resin  (1077),  or  silk 
(1078). 

[259.]  Excite  an  electrical  machine  (979),  warming  it 
carefully  (980).  Approach  the  knuckles  of  the  hand  to  the 
cylinder  or  plate,  and  observe  the  brashes  and  sparks  of 
electricity  which  dart  about  them  and  the  machi&e  (982), 
when  the  latter  is  in  good  order.  Put  the  prime  conductor 
(983)  into  its  place,  and  then  take  sparks  from  it  to  the  hand, 
or  a  metallic  ball.  Warm,  a  Leyden  jar,  charge  and  dis- 
charge it  (990).  Remark  for  how  long  a  period  the  charge 
can  be  retained  by  the  jar  (991). 

[260.]  Pass  the  charge  of  the  Leyden  jar  through  the 
eudiometer  wires  (988);  pass  it  also  through  *ihin  wires  so 
as  to  ignite  them.  Detonate  an  explosive  mixture  of  gases 
(997),  in  the  eudiometer  tube  over  water  (994),  and  also 
over  mercury.  Insulate  the  jar  when  required,  on  a  plate  of 
wax,  glass,  or  mica  (1074). 

[261.]  Make  a  small  electrophorus  (1007,  1011),  excite 
it  (1009),  observe  the  sparks  given  by  it  to  the  knuckle, 
charge  a  warmed  Leyden  jar  (990)  by  it  (1010),  and  use 


ELECTRICITY.  663 

the  jar  to  detonate  a  mixture  of  gases  (997)  in  the  eudiome- 
ter tube  (999). 

[262.]  Charge  a  voltaic  battery  (1025),  and  bring  it  into 
an  efficient  state  (1026);  try  the  discharge  between  its  poles 
by  charcoal  points  (1030),  and  observe  the  intensity  of  the 
light  produced.  Ignite  some  fine  wires  by  discharging  the 
electricity  through  them  (1073).  Immerse  the  poles  in  wa- 
ter contained  in  a  glass  (1037,  1046),  and  remark  the  decom- 
position which  takes  place.  Decompose  saline  solutions 
contained  in  tubes  (1046),  using  platinum  foil  to  extend  the 
surface  of  contact  (1038).  CollecJ  the  gases  (1049)  evolved 
during  the  decomposition  of  water,  and  examine  them  (950), 
as  to  their  qualities  and  nature ;  that  at  the  positive  pole 
will  be  oxygen,  that  at  the  negative  pole  hydrogen  (1050). 
Remark  the  double  quantity  of  hydrogen  produced  in  the 
experiment  as  compared  to  the  oxygen  evolved. 

[263.]  Observe  the  magnetic  properties  of  a  wire  (1040) 
connecting  the  poles  of  the  battery  just  referred  to  (1035). 
Place  a  magnetic  needle  under  and  over  the  wire,  and  re- 
mark the  influence  of  the  wire  upon  it  (1079).  Dip  a  part 
of  the  connecting  wire  into  iron  filings,  they  will  be  attract- 
ed in  rings,  as  it  were,  surrounding  every  part  of  the  wire, 
and  not  in  a  particular  part  only,  as  is  the  case  with  a  com- 
mon magnet.  Twist  the  wire  which  connects  the  poles  into 
a  helix,  then  place  a  thick  needle  or  a  small  bar  or  steel  in 
this  helix  for  a  moment,  break  the  voltaic  communication 
(1040),  remove  the  steel  bar,  and  observe  how  suddenly  it 
has  been  rendered  a  magnet. 

[264.]  Take  a  piece  of  zinc  and  a  piece  of  silver,  and  ob- 
serve their  peculiar  electric,  effect  upon  the  tongue  (1066); 
their  effect  also  upon  frogs,  fish,  worms,  or  other  small  ani- 
mals. Remark  the  power  of  the  two  metals,  when,  being  in 
contact,  they  are  immersed  in  a  weak  acid  (1062).  Ascer- 
tain by  the  tongue  the  power  of  a  fragment  of  metal,  and 
another  of  glass  or  stone  (1066),  with  respect  to  the  conduc- 
tion of  electricity. 

[265.]  Make  a  little  voltaic  battery  of  halfpence  or  disc* 
of  copper,  with  pieces  of  zinc  (1059),  and  flannel  moistened 
in  dilute  acid  (1026).  Discharge  it  through  charcoal  (1030); 


664  LUTES — CEMENTS. 

try  the  conducting  power  of  different  specimens  of  charcoal ; 
heat  fine  platinum  wire  red  hot  (1073),  decompose  water 
and  saline  solutions  by  it  (1049),  and  show  the  magnetic  in- 
fluence which  a  wire  connecting  its  extremities  (1040)  has 
over  a  magnetic  needle  (1079). 

[266.]  Precipitate  a  portion  of  copper  from  a  solution  of 
the  sulphate,  in  a  platinum  crucible  (1065,  523),  by  Dr  Wol- 
laston's  method ;  wash  the  copper  precipitated  on  the  plati- 
num, and  afterwards  dissolve  it  from  the  vessel  by  a  little     . 
pure  nitric  acid. 

XVIII.  Lutes.     Cements. 

[267.]  Lute  a  glass  retort  (489,  1084)  with  a  coating  of 
uniform  thickness  (1087),  attending  carefully  to  the  drying 
(1088),  and  bringing  it  ultimately  into  a  state  fit  for  use. 

[268.]  Make  a  comparatively  moist  lute  (1090),  some 
straw  chaff,  or  other  similar  substance  (1092)  having  been 
mixed  with  it  (1093).  Coat  a  phial  with  it  uniformly  (1087), 
that  when  dry  it  may  be  ready  for  the  preparation  of  pyro- 
phorus. 

[269.]  Coat  an  earthenware  (699)  or  glass  tube  (703) 
with  stiff  lute  (1084),  and  surround  it  with  a  band  of  canvass 
(1094). 

[270.]  Fix  one  crucible  firmly  in  another  (648)  by  lute, 
then  fix  the  double  crucible  upon  a  third  as  a  stand  (673, 
1101). 

[271.]  Cement  a  bent  tube  to  the  neck  of  a  Florence 
flask  (373,  484),  by  Parker's  cement  (1107),  or  plaster  of 
Paris  (1108).  A  flask  of  this  kind  is  competent  to  the  pre- 
paration of  carbonic  oxide  over  a  crucible  furnace  fire  (158). 
A  mass  of  the  cement  should  in  the  first  place  be  put  round 
the  tube  and  left  to  harden  ;  this  being  cut  into  a  conical 
form,  and  ground  slightly,  will,  with  very  little  management, 
close  the  mouth  of  the  Florence  flask  accurately,  and  thus 
form  a  useful  gas  bottle  (746). 

[272.]  Make  a  tight  joint  between  a  retort  and  a  receiver 
(475)  with  bladder  and  string  (1116),  or  with  a  fat  lute 
(1106),  or  with  paste  and  paper  (1117). 


BLOWING  AND  CUTTING  OP  GLASS.  665 

[273.]  Connect  apertures  in  tubular  arrangements  by 
means  of  caoutchouc  connecters  (448,  1122). 

[274.]  Examine  the  bottles  containing  solutions  of  muriatic 
acid  and  ammonia,  to  ascertain  whether  the  stoppers  are  tight 
or  leaky  (1130).  Examine  the  gas  holder,  exp.  228,  as  to 
the  existence  of  leaks  about  the  body  (810),  or  the  pipes 
connected  with  it  (1130). 

XIX.  Blowing  and  cutting  of  Glass. 

[275.]  Bend  a  piece  of  glass  tube  into  a  syphon  (1154). 

[276.]  Make  some  tubes  (1165)  closed  at  one  end  (910); 
expand  the  open  extremity  of  one  or  two  into  aflanch  (1147); 
contract  the  apertures  of  others  by  scissors,  so  as  to  form  a 
neck  (1163);  bend  some  of  them  into  tube  retorts  (924, 1175). 

[277.]  Close  one  of  the  open  extremities  of  a  short  piece 
of  tube  (1173). 

[278.]  Soften  the  middle  of  a  piece  of  tube  (1134),  and 
thicken  it  into  a  ring  (1200),  then  draw  it  out  into  a  con- 
tracted neck  (1175). 

[279.]  Make  a  tube  funnel  (1176, 924),  and  a  tube  syringe 
(547,  1181). 

[280.]  Blow  some  glass  into  frost  (1 194).  Blow  a  bulb  at 
the  end  of  a  piece  of  tube  (1194,  1196).  Expand  the  angle 
of  a  tube  retort  (924,  1197)  in  the  particular  direction  before 
explained  (956),  that  it  may  answer  the  purpose  of  a  tempo- 
rary retort  and  receiver  for  gases.  Make  a  separator  (558, 
1197).  Make  a  few  candle  crackers  (1199). 

[281.]  Join  two  pieces  of  tube  together  (1200).  Seal  a 
platinum  wire  into  a  tube  (1201)  for  the  purposes  of  electri- 
cal decomposition  (1046).  Make  a  small  detonating  eudi- 
ometer (994),  and  then  graduate  it  (127). 

[282.]  Use  quill  lubes  (910,  1207)  with  a  common  spirit- 
lamp  (199),  and  the  mouth  blow-pipe  (218).  With  these 
make  some  closed  tubes  (910, 1165);  some  small  tube  retorts 
(1175),  expanding  the  bulb  or  body  of  a  few  (1194),  so  as 
to  make  them  more  capacious ;  some  tube  receivers  (929) 
and  other  useful  apparatus ;  performing  the  same  operations 
in  the  small  way,  which  have  been  directed  upon  a  larger 
scale. 

41 


666  CLEANLINESS  AND  CLEANSING. 

[283.]  Seal  up  some  water  hermetically  in  a  tube  (1188, 
1184),  not  leaving  more  than  half  an  inch  between  the  sur- 
face of  the  water  and  the  extremity  last  closed.  In  the  same 
manner  seal  up  some  ether  in  a  tube  hermetically  (1189), 
leaving  about  li  inches  between  the  fluid  and  the  extremity 
to  be  sealed,  and  make  the  glass  thick  and  strong  (1185). 
Practise  the  same  operation  by  sealing  up  some  fragments 
of  sulphur  in  a  tube  (1184).  The  operation  may  be  consi- 
dered as  well  done  when  the  end  is  made  smooth  and  strong, 
without  melting  the  included  sulphur  at  a  distance  of  li  or 
1§  inches. 

[284.]  Seal  up  some  water  hermetically  in  a  tube  ex- 
hausted of  air  (1193). 

[285.]  Cut  a  piece  of  tube  about  twelve  inches  long  into 
two  (1152);  make  each  of  these  into  two  tubes  closed  at  one 
end,  one  about  4  and  the  other  2  inches  long  (1166).  Take 
a  piece  of  tube  with  a  fractured  and  irregular  termination, 
and  cut  it  off  straight  and  level  (1152)  within  half  an  inch 
of  the  extremity,  or  else  make  the  termination  nearly  straight 
by  rasping  off  (1227)  the  irregularities. 

[286.]  Before  dismissing  broken  apparatus  to  the  waste 
glass  box,  collect  it  on  a  tray,  and  then  cut  up  old  retorts, 
flasks,  or  glasses,  into  dishes,  by  iron  rings  (1212)  or  a  hot 
iron  rod  (1214);  cut  off  the  tops  of  fractured  Florence  flasks 
(1212),  and  make  the  lower  part  into  basins,  and  convert  old 
jars  or  bottles  into  shorter  jars  (1222)  by  the  hot  iron  (1214). 

[287.]  Take  every  opportunity  of  becoming  expert  in 
loosening  (12&5)  and  removing  glass  stoppers,  which  have 
become  fixed  in  the  bottles  (741);  in  cutting  pieces  of  crown 
glass  into  useful  forms  (1227,  &c.)  by  means  of  a  file  (1224), 
and  in  crushing  the  edges  of  fragments  (1227,  &c.),  so  as  to 
bring  them  into  serviceable  shape. 

XX.  Cleanliness  and  Cleansing. 

[288.]  The  practice  corresponding  to  this  division  of  the 
volume  will  be  abundantly  dictated  by  the  wants  which  will 
occur  the  instant  the  student  commences  his  progress  in 
experimental  chemistry.  It  will  be  well,  however,  that  he 
should  try  to  dry  the  insides  of  a  retort,  a  flask,  and  a  bottle. 


USES  OF  THE  SCALE — MISCELLANEA.  667 

which  have  been  washed  clean,  and  observe  how  effectually 
and  readily  he  may  do  it  by  the  methods  described  (1251, 
102).  He  should  grease  or  wax  a  stopper  (433,  741)  with 
the  precautions  given,  and  minutely  observe  the  degree  of 
resistance  and  kirfd  of  feeling  occasioned  when  it  is  properly 
lubricated  (433). 

[289.]  A  portion  of  foul  mercury  should  be  rendered  pure 
and  clean  by  Dr  Priestley's  method  (1282).  Another  por- 
tion, by  nitrate  of  mercury  (1283),  and  some  that  is  dusty  and 
foul  should  be  cleaned  by  sugar  and  agitation  (1273,  &c.). 

XXII.  Uses  of  the  Scale  of  Equivalents,  fyc. 

[290.]  Ascertain  by  the  scale  (1305)  the  quantity  of  nitric 
acid  required  to  dissolve  473  grains  of  carbonate  of  lime 
(1319),  and  the  quantity  of  crystallized  carbonate  of  potassa 
(1320)  required  to  precipitate  the  resulting  nitrate. 

[291.]  Tell  by  the  scale  how  much  sulphuric  acid  is  con- 
tained in  the  sulphate  of  baryta  of  experiment  102. 

[292.]  Ascertain  how  much  muriatic  acid  and  baryta 
(1318)  are  indicated  in  the  chloride  of  silver  and  sulphate 
of  baryta  of  experiment  103. 

[293.]  Observe  by  the  scale  how  much  metallic  copper  and 
oxide  of  copper  (1321)  may  be  expected  in  experiment  108. 

[294.]  Ascertain  the  composition  of  250  grains  of  crys- 
tallized sulphate  of  magnesia  as  to  its  earth,  acid,  and  water 
(1323);  and  also  as  to  the  sulphur,  oxygen,  and  hydrogen,  in 
the  acid  and  water  of  the  salt  (1321). 

[295.]  Ascertain  by  the  scale  (1321)  the  points  expressed 
p.  588,  relative  to  300  grains  of  sulphate  of  copper. 

[296.]  What  quantities  of  lime,  baryta,  strontia,  magnesia, 
potassa,  and  soda,  will  neutralize  320  grains  of  dry  sulphuric 
acid  (1315,  1318),  and  what  quantities  of  their  carbonates 
will  produce  the  same  effect1? 

[297.]  Ascertain  all  these  points  by  calculation  from  a 
table  of  equivalents  (1327),  and  observe  if  the  results  agree 
with  the  conclusions  arrived  at  by  means  of  the  scale  (1310). 

XXIII.  Miscellanea. 
[298.]  Make  some  hydrogen  from  a  few  pieces  of  zinc  and 


668  MISCELLANEA. 

a  little  dilute  sulphuric  acid,  in  an  oiled  paper  vessel  (1335); 
conduct  it  through  paper  tubes  (1337)  into  a  trough  made  of 
a  soup  plate  or  a  basin  (732),  and  receive  it  into  oiled  paper 
tubes  (1337,  1339),  which  will  answer  the  purpose  of  jars 
(946).  In  these  test  its  inflammability,  and  observe  its  other 
qualities,  and  remark  with  how  simple  an  apparatus  these 
and  many  other  such  experiments  can  be  made.  Attach  the 
edges  of  oiled  paper  vessels  which  are  to  be  air  and  water 
tight  for  a  time,  by  a  little  soft  cement  (1342,  1125). 

[299.]  Heat  the  interior  of  a  steam-bath  (271),  by  steam 
generated  in  a  kettle  (272),  and  conducted  from  its  spout  by 
oiled  paper  tubes  (1338).  Even  the  bath  itself  may  be  made 
of  a  few  pieces  of  wire  or  stick,  and  oiled  or  wax  paper. 

[300.]  Test  a  weak  mixed  solution  of  sulphate  of  copper 
and  muriate  of  lime  in  paper  vessels  (1335),  for  all  the  proxi- 
mate elements. 

[301.]  Pour  a  few  drops  of  a  weak  solution  of  phosphate 
of  potassa  or  soda  upon  one  part  of  a  sheet  of  white  paper, 
and  a  few  drops  of  a  weak  solution  of  arsenite  of  potassa 
upon  another  part  of  the  same  paper  (1335).  Draw  a  piece 
of  nitrate  of  silver  through  the  two  portions,  pressing  on  the 
paper  at  the  same  time,  and  observe  the  differences  in  cha- 
racter between  the  two  precipitates. 

[302.]  Boil  half  a  pint  of  water  in  a  paper  vessel  (1335). 

[303.]  Make  (563)  and  crystallize  a  solution  of  alum  (564) 
in  oiled  or  waxed  paper  vessels  (1335);  separate  the  more 
perfect  crystals,  and  preserve  them  in  paper  tubes  (1341). 

[304.]  Heat  a  little  white  arsenic  on  platinum  foil  (1353) 
by  a  small  spirit-lamp  flame  (199,  205).  Then  heat  a  por- 
tion on  the  foil,  but  with  a  large  flame  (205),  and  incline 
the  foil  that  the  hydrogen  of  the  flame  may  mix  with  the 
vapours  of  arsenic ;  or  heat  the  arsenic  on  a  hot  coal. 
Observe  the  difference  in  the  odour  occasioned  in  these  two 
cases:  the  odour  when  developed  is  dependent  upon  the 
reduction  of  part  of  the  white  arsenic  to  the  metallic  state. 

[305.]  Draw  out  a  small  capillary  tube  (1176),  examine 
its  bore  by  a  small  quantity  of  mercury ;  graduate  it  (1370) 
and  make  it  into  an  air-guage  (1369). 

[306.]  Retain  a  platinum  wire  in  a  state  of  ignition  in 


MISCELLANEA.  669 

the  vapour  of  ether,  over  a  small  portion  of  that  fluid  in  a 
glass. 

[307.]  Sublime  (935)  a  little  cinnabar  in  a  tube  (910)  not 
more  than  Is  inches  in  length  (1333). 

[308.]  Sublime  some  napththaline  from  one  tube  (938) 
into  a  long  open  tube  fixed  to  the  smaller  by  a  perforated 
cork  (1331,  465). 

[309.]  Put  a  fragment  of  camphor  at  the  bottom  of  a  tube 
two  feet  long,  and  observe  its  odour  by  means  of  another 
tube  (1365). 

[310.]  Try  the  phosphorescence  of  fluor  spar,  and  differ- 
ent kinds  of  carbonate  of  lime  (1383). 

[311.]  Mix  equal  volumes  of  hydrogen  and  chlorine  over 
water;  transfer  portions  of  the  mixture  into  glass  tubes 
(910,  946),  using  paper  funnels  (1342),  if  there  be  occasion 
for  such  convenience;  then  expose  these  mixtures  to  sun 
light  (6,  1387),  and  observe  the  explosion  which  immediately 
takes  place. 

[312L]  Observe  the  effect  of  solar  light  and  day  light  upon 
nitrate  of  silver  and  chloride  of  silver  (6, 1388)  spread  upon 
paper.  Make  Mr  Wedgwood's  experiment,  using  magic 
lantern  glasses  for  the  purpose. 

[313.]  Make  a  magnet  (1399).  Make  a  magnetic  needle 
(1399),  suspending  it  in  any  convenient  way  (1398).  Try 
a  piece  of  Elba  iron  ore  by  this  needle  (1391),  reiterating 
the  approximations,  or  adopting  Hauy's  method  (1394). 

[314.]  Write  legibly  on  a  glass  tube  with  a  scratching 
diamond  f974),  the  tube  being  from  one  half  to  one  quarter 
of  an  inch  in  diameter. 

[315.]  Cut  a  crucible,  or  stopper,  with  its  cover  and  a 
support,  out  of  soft  Windsor  brick  (1354),  and  make  some 
boxwood  charcoal  in  it  (1033).  . 

[316.]  Evaporate  a  mineral  water  to  one-eighth  its  ori- 
ginal bulk  (594),  and  then  test  it  on  glass  plates  (1348). 
Crystallize  a  solution  of  nitre  on  a  glass  plate  (565,  1348); 
also  a  solution  of  salt,  and  examine  the  forms  of  the  crystals 
(580). 

[317.]  Freeze  a  little  water  in  a  cup  of  tin  foil  (1349),  by 
a  mixture  of  ice  and  salt. 


670  MISCELLANEA. 

[318.]  Etch  on  glass  by  fluoric  acid  (1366),  using  a  leaden 
dish  (1367,  1350),  for  the  mixture  of  acid  and  fluor  spar. 

[319.]  Make  a  single  electrical  circuit  (1352,  1062);  ob- 
serve its  effect  in  deflecting  and  otherwise  influencing  the 
magnetic  needle. 

[320.]  Precipitate  a  solution  of  acetate  of  lead  by  zinc 
foil  (1352);  test  the  solution  for  lead  in  paper  vessels  (1335), 
that  the  completion  of  the  precipitation  may  be  ascertained. 

[321.]  Burn  filaments  of  zinc  foil  (1352)  in  the  flame  of 
a  lamp  or  candle. 

[322.]  Fuse  a  little  piece  of  lead  on  platinum  foil  (1353), 
and  remark  the  instant  liquefaction  of  the  foil  in  consequence 
of  the  formation  of  an  alloy  (662).  Even  sulphuret  of  lead 
will,  on  trial,  be  found  to  have  a  similar  action.  Heat  a 
little  chloride  of  silver,  or  a  little  oxide  of  iron  on  the  foil 
to  whiteness;  no  harm  will  result  (1353). 

[323.]  Distinguish  wires  of  silver  and  platinum  by  their 
power  of  conducting  heat  (1358). 

[324.]  Sublime  a  little  calomel  in  a  tube  (935)  enveloping 
the  tube  about  half  way  from  the  bottom  (1351)  so  as  to  pre- 
serve the  heat  (716),  and  prevent  condensation  on  that  space; 
ultimately  crack  the  end  of  the  tube  in  mercury  (1356). 

[325.]  Place  a  board  within  two  or  three  inches  of  a  hot 
furnace;  protect  one  half  of  it  by  a  plate  of  tin  (1359),  and 
observe  the  difference  between  that  and  the  other  half. 


HARE'S  METHOD  OF  SEPARATING  CARBONIC  ACID,  &c.     671 


APPENDIX. 

Apparatus,  contrived  by  Dr  Hare,  for  separating  carbonic 
oxide  from  carbonic  acid,  by  means  of  lime  water. 


672     HARE'S  METHOD  OF  SEPARATING  CARBONIC  ACID,  &c. 

"  Lime  water  being  introduced  in  sufficient  quantity  into 
the  inverted  bell-glass,  another  smaller  bell-glass  C  is  sup- 
ported within  it  as  represented  in  this  figure.  Both  of  the 
bells  have  perforated  necks.  The  inverted  bell  is  furnished 
with  a  brass  cap  having  a  stuffing-box  attached  to  it,  through 
which  the  tube  D  of  copper  slides  air-tight.  About  the 
lower  end  of  this  tube,  the  neck  of  a  gum  elastic  bag  is  tied. 
The  neck  of  the  other  bell  is  furnished  with  a  cap  and  cock, 
surmounted  by  a  gallows-screw,  by  means  of  which  a  lead 
pipe  P  P,  with  brass  knob  at  the  end  suitably  perforated 
may  be  fastened  to  it,  or  removed  at  any  moment.  Suppose 
this  pipe,  by  aid  of  another  brass  knob  at  the  other  extremity, 
to  be  attached  to  the  perforated  neck  of  a  very  tall  bell-glass 
filled  with  water  upon  a  shelf  of  the  pneumatic  cistern:  on 
opening  a  communication  between  the  bells,  the  water  will 
subside  in  the  tall  bell-glass,  over  the  cistern,  and  the  air  of 
the  bell-glass  C  being  drawn  into  it,  the  lime  water  will  rise 
into  and  occupy  the  whole  of  the  space  within  the  latter. 
As  soon  as  this  is  effected,  the  cocks  must  be  closed  and  the 
tall  bell-glass  replaced  by  a  small  one  filled  with  water,  and 
furnished  with  a  gallows-screw  and  cock.  This  bell  being 
attached  to  the  knob  of  the  lead  pipe,  to  which  the  tall  bell 
had  been  fastened  before,  the  apparatus  is  ready  for  use. 
I  have  employed  it  in  the  new  process  for  obtaining  carbonic 
oxide  from  oxalib  acid,  by  distillation  with  sulphuric  acid 
in  a. glass  retort.  The  gaseous  product  consists  of  equal 
volumes  of  carbonic  oxide  and  carbonic  acid,  which,  being 
received  in  a  bell-glass  communicating  as  above  described 
by  a  pipe  with  the  bell-glass  C,  may  be  transferred  into  the 
latter,  through  the  pipe,  by  opening  the  cocks.  As  the 
gaseous  mixture  enters  the  bell  C,  the  lime  water  subsides. 
As  soon  as  a  sufficient  quantity  of  the  gas  has  entered,  the 
gaseeus  mixture  may,  by  means  of  the  gum  elastic  bag 
and  the  hand,  be  subjected  to  repeated  jets  of  lime  water, 
and  thus  depurated  of  all  the  carbonic  acid.  By  raising 
the  water  in  the  outer  bell  A,  the  purified  carbonic  oxide 
may  be  propelled,  through  the  cock  and  lead  pipe,  into  any 
vessel  to  which  it  may  be  desirable  to  have  it  transferred," 


INDEX. 


Acetic  acid,  strength  of,  ascertained, 

295 
Add  for  alkalimetry,  292,  293 

voltaic  trough,  469 
Addimitery,  296 
Adds,  their  uses  as  solvents,  199 

strengths  ascertained,296 
tested  for,  288 
filters  for,  258 
Adjustment  of  liquids,  48 
Aerometer,  Hall's,  402 
Aikiris  furnace,  103 
Air  exhausted  from  vessels,  391,  393 
weighed,  402 
hot,  a  heating  agent,  140 

procured,  140 
chamber,  warm,  280 
furnace,  102 
gauges,  529.  608 
holder,  367 
jars,  334 

tube,  431 
cleansed,  559 
pump,  390 

examined,  390 
preserved.  29.  392 
exhaustion  by,  390,  394 
evaporation  under,  273 
thermometer,  152 
Alcohol,  its  use  as  a  solvent,  197 
fuel,  110. 114 
its  flame,  105 
decomposed  in  tubes,  527 
bath,  140 

thermometer,  147.  149 
Akmbic,  237 
Alkalies  tested  for,  288 

strength  ascertained,  292.  295 
Alkalimeter  acid,  292,  293 

tube,  291 

Alkalimetry,  291.  295.  642 
Alkaline  solvents,  200 

earths  decomposed  in  tubes,  329 

647 

Alloys  made,  311 
Almond  paste,  506 
4K 


Amalgam  applied  to  silk,  450 
Ammoniacal  gas  collected  in  bottles, 

375 
prepared    and     experimented 

with,  651 
Analysis,  pulverisation  for,  169 
Annealing  of  glass,  481 
Anthracite  substituted  for  coke,  96 
Apertures  closed  temporarily,  439 
Apparatus  room,  its  use,  29 
Aqueous  solutions  crystallized,  265 
Argand's  lamp,  115 

t  double  wicked,  116 

) 

Sags  for  gas,  371 
Balance,  31,  621 

Black's  delicate,  70 
Ritchie's  delicate,  72 
substitute  for,  70 
varieties  of,  32 
its  theory,  34 

indications,  36.  56 
setting,  36 
examination,  34.  37 
preservation,  29 
Barometer  observed,  349 
Barometric  pressure,  400 
Basins,  earthenware,  181.  340 

examined,  181 
glass,  181.  545 
evaporating,  181.  266 
metallic,  181 
sublimations  in,  238 
in  the  sand-bath,  186 
cleansed,  559 
covered  with  paper,  267 
Baths,  alcoholic,  140 
mercurial,  1S8 
metal,  139 
oil,  139 

sand,  99.  135.  186 
solution,  138 
steam,  141 
water,  135 
Battery,  electric,  458 

voltaic,  469*  (set  Voltaic  pile) 


674 


INDEX. 


Bellows,  104, 105 
Sending  of  glass,  511.516.  519 
Sennet's  electrometer,  463 
Black  lead  crucibles,  298 

flux,  313 

Slack's  balance,  70 
Bladder  for  joints,  505 
Bladders  for  gases,  371 
Blast  furnace,  103.  307  ^ 

its  operation,  309 
Slocks,  adjusting,  25 
Blowing  of  glass,  511.517.  536.  665 
Blow-pipe,  117 

use  of,  120.  626 

fts  powers,  122.  125.  128 

temperature  of  flame,  126 

action  of  mouth,  120. 122 

its  theory,  125 

jet,  119 

lamp,  123 

supports,  127 

charcoal,  128 
Black's,  118 

Clarke's,  135  ^ 

common,  118 
glass,  119 
Gurney's,  135 
Hare's,  132.  134 
Leeson's,  134 
Marcet's,  133 
oxygen,  133.  370 
oxy-hydrogen,  134 
Silliman's,  332 
temporary,  119. 130.  543 
Wollaston's,  118 
table,  26.  129.  511 
its  place,  26 
how  used,  129 
Slue  pots,  298 
Boiling  under  pressure  in  tubes,  63. 

417 

Book,  laboratory  note,  29.  576 
Boracie  acid  on  turmeric  paper,  290 
Borax,  319 
Bottles  for  gases,  374 

specific  gravity,  59 
their  stoppers  loosened,  562 
caoutchouc,  372 
cleansed,  562.  566 
dried,  561,  562 
Boxwood  charcoal,  473 
Breaking  of  bodies,  161.  163 
Brick,  soft,  or  Windsor,  601 
Bricks,  their  uses,  27.  601 
Broken  glass  cut  up,  546.  549 
Brunswick  black  varjiish,  555 
Bulbs  of  glass  blown,,  536 
filled  with  liquid,  63 


Bulbs  for  specific  gravity,  65.  69.  538 
Camphor  pulverised,  168 
Canvas,  its  use  over  lute,  316.  499 
Caoutchouc  connectors,    217.    319. 

383. 506 
gas  bottles,  373 
sheet,  218.  220.  374.  378.  384. 

510 

dropping  bottle,  196 
covering  for  corks,  593 
permeated  by  gases,  134.  372, 

373 

Cap  cement,  507 
Capillary  tubes,  528 

graduated,  608 
Caps  for  retorts,  380 

attached,  381.  397. 

656 

their    place    sup- 
plied, 382 
Capsules,  metallic,  112.  371 

sublimations  in,  238 
Carbonate  of  lime  precipitated,  246 
Carbonic  acid  gas  prepared  and  ex- 
perimented with,  649 
oxide   prepared    and     experi- 
mented with,  653 
Cards,  use  of,  169 
Cavendish's  gas  transferrer,  358 
Cement,  iron,  505 
Parker's,  503 
Roman,  503 
soft,  272.  507 
yellow  wax,  507 
for  caps,  507 
powdered  gum,  509 
Cements,  495.  507.  664 
Chalk-stone,  drying,  283 
Charcoal,  108.  128 
pulverised,  168 
its  reducing  powers,  315 
for  blow-pipes,  128 

voltaic  experiments,  473 
crucibles,  299 

Charge  for  voltaic  troughs,  469 
Charging  of  a  battery,  471 
flasks,  192 
retorts,  211 
Chemical  action,  deceptive  appear- 
ance of,  180 
equivalent,  584 
Ohemistry,  tube,  413.  658 
Chloride  of  silver  precipitated,  245 
Chlorine  gas  collected,  331.  653 
prepared    and     experimented 

with,  653 
preserved,  374 
solution  of,  made,  389 


INDEX. 


676 


Cleanliness,  626.  553.  666 

regulations  for,  554.  566.  575 
Cleansing,  553.  626 
flux,  567 
wires,  556 
of  air  jars,  559 
bottles,  562.  566 
copper,  567 
crucibles,  platinum,  567 
evaporating  basins,  559 
flasks,  560 
glasses,  557 
mercurial  trough,  568 
mercury,  568 
mortars,  567 
retorts,  561 
tubes,  558 

Closing  of  tubes,  523.  530.  534 
Coal,  107 

Coated  vessels,  496.  499 
Coating  of  retorts,  flasks,  and  cruci- 
bles, 496 

how  performed,  496.  500 
to  sustain  a  high  temperature, 

496 

to  prevent  passage  of  air,  502 
dried,  497,  498 
repaired,  498 
strengthened,  498 
supported  in  the  fire,  235.  501 
contraction  of,  in  the  fire,  500 
Cocks,  gas,  376 

Hare's  valve,  379 
examined,  377 
tightness  of,  358.  382 
Coke,  96. 108 

Staffordshire,  108 
Collars,  378 
Collection  of  gas,  338 
Coloured  tests,  284,  285.  641 
fluids,  285 
papers,  285 
precautions,  290 
Combination  of  bodies  influenced, 

175.  325 

effected  in  tubes,  327 
Comminution,  156.  627 
Compound  bodies,  their  definite  na- 
ture, 582 

Compression  of  gases,  396.  608 
Condensation,    in   distillation,    207. 

216.  220 

on  retort  neck,  225 
of  gases  in  tubes,  440.  444.  608 
precautions,  442 
cyanogen,  440.  444 
muriatic  acid,  444 
sulphurous  acid,  444 


Conduction,   of   electricity,   indica- 
tions, 448 

Rousseau's  test,  491 
heat  applied,  601 
Cone,  heating,  188.  190.  213 
Connecting  pieces,  383 
Connection  of  tubes,  318 

pneumatic    apparatus, 

376 
Connectors,  383 

of  caoutchouc,  217-  219.  383. 

506 

Contact,  voltaic,  475 
Cooling  mixtures  made  and    used, 

220 

Copper,  cleansed,  567 
divided,  174 

foil  cases  to  tube s,  324.  600 
leaf,  600 

plate,  its  uses,  600 
pneumatic  trough,  330 
precipitated,  246 
wire,  uses  of,  598 
Cork  handles  to  tubes,  416.  527 
Corks,  uses  of,  27.  47.  225.  416.  593 
covered  with  caoutchouc,  593 
Cornish  crucibles,  297.  299 
Correction  of  gas  volume,  397 

for  moisture,  403, 

404 

pressure,  400 
temperature, 

398 

Cotton  syphon,  261 
Counterpoising,  33.  45.  621.  623 
Course  of  inductive  and  instructive 

practices,  620 
Covering  of  vessels,  261.  278 

with  paper,  267 
Cowers  of  glass,  261.  549 

paper,  267 
to  crucibles,  307 
filters,  256,  257 
glasses,  261 
Crack  in  glass  directed,  547.  551 

stopped,  451 
Cream  of  tartar,  313 
Crown  glass  divided,  550 
Crucible  covers,  305.  307 
furnace,  92.  305 
made,  92 
arranged,  94 
used,  305 
jacket,  305 
operations,  296.  311.  643 

precautions,  310 
shelter,  309 
stoppers,  299 


676 


INDEX. 


Crucible  supports,  304.  307 
Crucibles,  92.  296 

appropriated,  302 
heated,  304 

by  furnaces,  305 
lamps,  112.  304 

and  blow-pipe, 

.125.  304 
and  jacket,  305 
sublimation  in,  238 
black  lead,  298 
cleansed,  567 
coated,  496 
Cornish,  297.  299 
charcoal,  299 
double,  298 
earthen,  296.  298.  303 
English,  296 
gold,  301 
Hessian,  297,  298 
iron,  302 
lined,  299 
platinum,  300.  302, 

cleansed,  567 
silver,  265.  301 
temporary,  302 
Wedgewood's,  297 
Crude  tartar,  3 13 
Crystallization,  264.  639 
indications  of,  270 
influenced,  269 
how  effected,  265 
its  usefulness,  264 
of  metals,  271 
in  water,  265 

alcohol,  268 
by  cooling,  265.  267 
evaporation,  266 
fusion,  265.  271 
sublimation,  272 
Crystallizing  point,  265 
Crystals,  formed,  266 
dissected,  271 
dried,  284 
examined,  270.  272 
large,  267 

many  converted  into  one,  268 
appearances  influenced,  269 
Cubic  inch  bottles,  76 

measures,  77 

Cupboards,  their  arrangement,  23 
Cutting  diamond,  545 

of  glass  rod  or  tube,  518.  544 
crown  glass,  545.  550 
glass  by  diamond,  544.  549 
hot  iron,  546.  549 
rings,  545 


Cutting  old  glass,  545.  549 
Cyanogen  condensed,  440 

Daniell's  dissection  of  crystals,  271 

pyrometer,  155 
Decantation,  259.  637 
washing  by,  260 
of  gas  from  jars,  343 

from  tubes,  345 
Decoction,  203 

Decomposition,  voltaic,  479  (see  Vol- 
taic decomposition) 
in  tubes,  325 

influenced,  325 

Decrepitation  prevented,  170.  311 
Definite  nature  of  compound  bodies, 

582 

Deflagrating  jars,  334 
Degrees  of  the  thermometer,  145 
Deoxygenation  of  oxides,  315.  327 

of  metallic  solutions,  203 
Desiccating  tubes  for  gases,  405 
Desiccation,  276.  640 
in  close  vessels,  274 

tubes,  427 
of  crystals,  283 
gases,  405 
organic  matter,  279 

powders,  280 
Desiccators,  273.  276.  405 
Detonation  of  gases,  proportions  to 

be  used,  456 
by  electric  spark,  451 
precautions,  452.  455 
electrophorus  spark,  462 
Ley  den  jar,  453 
Diamond,  cutting,  545 
scratching,  78.  447 
pulverized,  170 
Differential  thermometer,  154 
Digestion,  183.  629 

in  tubes,  416 

Discharger,  electrical,  454.  460 
Discoloration  of  glass  removed,  513 
Dishes  for  gas  jars,  336 
Dissection  of  crystals,  271 
Dissolution,  178 
Distillation,  205.  419.  632 
ordinaiy,  206  • 
at  high  temperatures,  234 
products  of,  215 
in  close  vessels,  225.424 
dry  vessels,  230 
flasks,  233 
retorts,  212.  233 
iron  retorts,  236 
tubes,  417.  420 


INDEX. 


677 


Distillation  in  vacuo,  424 
facilitated,  214.  234 
of  nitric  acid,  229 

sulphurous  acid,  217-  222 
wine,  225 

Distilled  water  important,  27.  193 
Division  of  glass,  545^ 

matter,  156.  627 

its  use,  156.  184 
metals,  174 
silica,  174 
Drawers,  their  appropriation,  27 

cleanliness,  5.55 
Dropping  bottle,  196.  257.  414 
Drying  chamber,  280 
stone,  282 
of  flasks,  bottles,  and  retorts, 

561 

of  gases,  405 
Dryness  of  powders  examined,  280 

Earthenware  crucibles,  296.  298. 303 
reto4s,  236 
tubes,  316 
Earths,  alkaline,  soluble  in  sugar, 

200 

decomposed    in 

tubes,  329.  647 

Ebullition  irregular  prevented,  214 

under  pressure  in  tubes,  417 
Edges  of  glass  removed,  519.  552 
Effervescence  guarded  against,  193 
Egg  and  lime  lute,  504 
Electric  accumulator,  460 

discharge,  intensity  exalted,  453 
passed  through  wires,  454 
spark,  its  uses,  451 
Electrical  battery,  458 

communications,  453.  458 
condensers,  467 
discharger,454,  460 
insulation,  458.  492 
jar,  453 

examined,  453 

charged  by  electrophorus, 

462 

substitute  for,  459 
machine  excited,  449 

action  examined,  450 
preserved,  30.  451 
warmed,  449 
Electricity,  448 

practices  in,  662 
voltaic,  469 

conducting  power  for,  examin- 
ed, 488,  452 

Electro-magnetic  arrangements,  477. 
486.  494 


Ekctrometer,  nature  of  its  divergen- 
cies, 464.  466 
affected  by  contact  of  excited 

bodies,  464.  468 
affected  by  vicinity  of  do.  465 
its  indications  interpreted,  467 
electricity  examined  by  it,  466 
caoutchouc,  469.  466 
Coulomb's,  469 
Bennet's,  463 
Hare's,  469 

Henly's,  how  used,  458 
Singer's,  463 

Elcetrophorus,  made,  461.  463 
excited,  461.  463 
its  powers,  462 
Englisfi  crucibles,  296 
Engraving  on  glass,  606 
Equivalent  proportions,  584 
Equivalents,  their  nature,  583 
chemical,  584 
synoptic  scale  of,  581 
table  of,  592 
Escape  of  gases  from  mercury,  357. 

572 
Euchlorine  prepared  in  tube  retort, 

431 
Eudiometer,  detonation  of  gases  in, 

451.  454 

management  of,  455.  457 
wires,  453 
wires  fixed  in,  542 
Hare's,  492 
Ure's,  457 
Eupyrion,  28 
Evaporating  basins,  181 

cleansed,  559 

Evaporation,  266.  273. 430.  625 
minute,  280 
at  common  temperatures,  266. 

273 
by  currents,  276.  280.  430 

heat,  276.  430 
for  analysis,  276 
in  basins,  276 

close  vessels,  273.  276.  278 
open  vessels,  276 
platinum  crucible,  279 
tubes,  430 
the  air  pump,  273 

hot  air  chamber,  280 
of  destructible  matter,  279 
to  dryness,  276.  430 
Exhausted  tubes  sealed,  534 

vessels,  39,3 

Exhaustion  of  air,  390.  393 
Expansion  of  gas  by  heat,  399 
moisture,  403 


678 


INDEX. 


Experiments,  a  course  of,  620 
Explosion  in  tubes  guarded  against, 

432 
safe,  612 

Fahrenheit's  scale,  146 

Face,  masks  for  the,  611 

Fat  lute,  502 

Feathers,  uses  of,  255 

Feeding  tube  for  retort,  232 

Ferro-prussiate  of  iron  precipitated, 

249 
Files,  marking-  on  glass  with,  78 

metals  divided  by,  175 

to  cut  glass,  413 
Films  of  mercury,  569.  571 

their     influence, 

357.  571 
Filtering  paper,  248 

stands,  22.  248 

Filters,  their  substance,   247.  249. 
569 

charged,  253 

dried,  282 

folded,  250.  252 

large,  258 

made,  250 

moistened,  255 

plain,  250.  252 

small,  257 

strengthened,  253 

supported,  250.  253.  258 

for  acids,  258 
Filtration,  247-  258.  637 

precautions,  255.  257 

hot,  256 

'  washing  by,  254 
Flame,  its  heat,  110,  111.  124.  514 
Flasks,  their  use  in  solution,  186 

distillation,  213. 233 

powders  introduced  into,  192 

their  place  supplied  by  tubes, 
415-* 

necks  strengthened  by  waxed 
twine,  183 

used  as  receivers,  216.  225 
retorts,  233 

boiling  in,  187.  190 

evaporation  in,  278 

effervescence  in,  193 

cleansed,  560 

closed,  561 

coated,  496 

dried  within,  561 
'  heated,  187, 190 

supported,  188 

flint  glass,  182.240  v  * 

*  ' 


Flasks,  Florence,  182.  237. 240. 279. 

560 

Flint-glass  (Rux),3U 
Flints,  pulverized,  168 
Florence  flasks,  182.  233.  240.  279. 

393.  561 

Flues,  their  arrangement,  19.  192 
connecting,  97.  192 
temporary,  97 
Fluids,  decanted,  259 
heated  in  tubes,  63 
introduced  into  bulbs,  62 
separated,  262.  638 
mixed  in  tubes,  414 
Flux,  alkaline,  313 
argol,  313 
black,  313 
borax,  314 
cleansing,  567 
crude  tartar,  313 
cream  of  tartar,  313 
flint  glass,  314  L 
green  glass,  314      <f 
nitre,  313 
sal  enixum;  314 
white,  312 
Fluxes,  312 

applied,  315 
Foil,  copper  casing  to  tubes,  324. 

600 

platinum,  112.  600 
tin,  599 
Frigorific  mixtures  made  and  used, 

224 

Fuel,  26.  94.  107 
alcohol,  110.  112 
charcoal,  108 
coal,  107 
coke,  107 
gas,  117 
oil,  115 

Funnels,  194.  247.  344 
of  tube,  419.  529 

paper,  596 
for  filtration,  24f.  250 

gas,  336.  344 
stoppers  for,  262 
for  pouring,  212 

powders,  194.  211 
Furnace,  blast,  103,  104.  307 
Aikin's,  104 
powerful,  104.  307 
crucible,  92. 190.  235.  305.  320 
powers  of,  97 
increased,  95 
flue,  95 
fuel,  94  -••>*• 


INDEX. 


679 


Furnace,  crucible,  grate,  94 

Knight's,  102 

portable,  92 

table,  21.  97.  237.  305 
its  construction,  98 

tube,  320 

wind,  96.  102 

rings,  101 

stoppers,  94 

tube  operations,  316.  646 
Furnaces,  21.  92.  305 

their  situations,  109.  190 

protections  from,  109.  190 
Fusible  lutes,  502 
Fusion  of  alloys,  312 

metals,  312.  643 

crystallization  by,  271 

Gas  bags,  371 
bladders,  371 
bottles,  337 

bottles  of  caoutchouc,  372 
dishes,  336 

funnels,  336.  344.  346 
glasses,  336.  346.  431 
holder,  its  construction,  368 

uses,  369.  657 
jars,  mercurial,  334.  355 
plain,  334.  431 
stoppered,  334 
transfer,  335 
cleansed,  559 
lamps,  117 
.    measures,  76.  352 

Cavendish's,  352 
transferrer,  Cavendish's  358 
Hare's,  89.  361 
Pepys's,  359 
tubes,  336.  345.  383.  431 

generating,  434.  438 
Gaseous  manipulation,  329. 431 

tube,  420. 431 

Gases,  bodies  exposed  to,  392.  395 
bottles  for,  374 
escape  from,  over  mercury,  356. 

572 
expansion  of,  by  moisture,  403 

heat,  398 

measures  for,  76.  352 
management  of,  329.  648 
pressure  upon,  349.  362.  608 
quantities  of,  adjusted,  350 
temperature  of,  354 
transmission  of,  336 
their  volumes,  555 
bottled,  344.  374 
collected  over  mercury,    354. 
356.  651 


Gases  collected  over  water,  337. 420. 

648 

entirely  or  pure,  338 
in  a  gasometer,  364 
gas  holder,  369 
bottles,  375 
jars,  339 

from   voltaic  decom- 
position, 480 
compressed,  396.  610 
condensed  in  tubes,  440.  444. 

608 

precautions,  440.  443 
conducted  through  tubes,  384. 

447 
corrected,  397 

for  moisture,  404 
temperature,  398 
pressure,  400 
decanted,  343       ^ 

into  bottles,  344 
decomposed  by  voltaic  heat,  491 
detonated  in  an  eudiometer,  451. 

453,  454 
by  electric  spark,  451. 

462 
dissolved,  385.  389 

in  tubes,  439  I 

dried,  405 

by  tubes,  407 

sulphuric  acid,    406. 

408 

evolved,  337.  648 
examined  in  generating  tubes, 

434 

mercurial  receiver,  432 
heated  in  tubes,  325 
measured  over  mercury,  361 

water,  347 

in  jars,  348 .  350.  361 
tubes,  349. 351, 352. 

361 

corrections  for,  350 
mixed,  389 
retained,  339.  363 
transferred  over  mercury,  356. 

358.  652 
water,  343. 371. 

648 

from  jars,  343 
tubes,  345 
into  exhausted  ves- 
sels, 394 

by  dishes,  336.  340 
weighed,  403 

Thomson's  method,409 
Gasometer,  its  construction,  363 
use,  364 


680 


INDEX, 


Gasometer  adjusted,  365 
examined,  366 
mercurial,  366 

General  rules  for  young  experimen- 
ters,, 575 
Generating  gas  tubes,  432.  434.  436. 

438 

Glass,  a  bad  insulator,  494 
engraving  upon,  606 
writing  upon,  78.  447.  604 
stains  upon,  removed,  513 
green,  its  advantages,  239 

worked,  535 
-  »    ."crown,  cut,  550 

bulbs  blown,  536.  538 
covers,  549 
(flux),  314 
masks,.  612 
plates,  336.  598 
rods,  183.  518 
rods,  cut,  518.  552 
stirrers,  183.  518 
stoppers,  210.  335.  549 
ground,  552 
loosened,    335.    562. 

565 

syphon  made,  519 
syringes,  263.  529 
tubes,  318.  413.  523  * 

bent,  516,  519 
I   f  closed,  523.  527.  530 
cut,  518.  544 
fracture  of,  by  heat,  512. 

523 

heated,  320.  323 
joined,  539 
made,  523.  537 
sealed,  523.  527.  530 
'.;t          strength  of,  396 

wires  sealed  intp,  539 
annealed,  518 
bending  of,  511.  516.521 
blowing  of,  511.  516.  536 
broken,  cut  up,  545.  549 
cooled,  517 

cutting  of,  511.  518.  544.  665 
•  by  diamond,  545 
hot  iron,  546 
rings,  545 
discoloured,  513 
divided,  538 
drawn  out,  531.  534 
edges  removed,  519,  552 
grinding  of,  552 
heating  of,  512 
moulded,  516.  522 
rasped  into  form,  551 


Glass  silvered,  612 
softened,  515 
worked,  511.  625 
Glasses*  laboratory,  182.  240.  335 

cleanliness  of,  554 
cleansed,  557 
Glauber's  apparatus,  385 
Glue,  with  paper  or  cloth  for  a  junc- 
tion, 506 
Gold  crucible,  301 

divided,  176 

Graduation  of  capillary  tubes,  608 
jars,  88 

triple,  89 
thermometers,      144. 

152 
tubes,  77 

by  measuring,  84 
weighing,  78 
the  eye,  86 
minute,  87 

Granulation  of  metals,  174 
Grate,  furnace,  94 
Grease  removed  from  glass,  557 
Green  glass  tube,  535.  318 
Grinding  of  glass,  552 

stoppers,  552 

Gauges  for  condensed  air,,  529.  608 
Gum,  powdered,  509 
Gunter's  line  of  numbers,  585 

Hall's  aerometer,  402 
Hancock's  caoutchouc,  218 
Handles  of  paper  for  tubes,  416 
Hare's  measurer,  81.  361 
calorimotor,  491 
conjunctive  rods  for  voltaic  bat- 
tery, 478 
chyometer,  326 
eudiometer,  491 
hydrostatic  blow-pipe,.  132.  332 
improvements  in  voltaic  battery, 

484 

instruments  for  the  measure  and 
transference  of 
fluids,  89.  351. 
360.  654 

for  filtering  hot  li- 
quids, 256 
for  separating    im- 
miscible liquids, 
*    263 
for  adjusting;  fluids, 

49 

method  of  adjusting  surface  of 
pneumatic  trough,. 
343 


INDEX. 


681 


Hare's  method  of  forming  and  exam- 
ining peroxide  of 
chlorine,  436 
separating  carbonic 

acid,  671 
dividing  glass  tubes, 

546 

self-regulating  gas  reservoir,  376 
sliding-rod  gas  measurer,  .351 
use  of  flexible  lead  tubes,  384 
borax  in    decomposition 

of  water,  483 
mirror  in  explosions,  616 
oiled  leather  gas  bags,  373 
wire  gauze  to  support  re- 
torts, &c.,  189. 256.  318. 
322 

valve  cock,  379 
Haiiy's  test  of  magnetism,  618 
Heat,  sources  and  management  of, 

91.  304.  491.  625 
retained,  141.  144.  229.  256 
increases  chemical  action,  185 

solubility,  180.  184 
of  flame,  111 

blow-pipe  flame,  124.   213. 

514 

voltaic  discharge,  491 
applied  to  flasks,  &c.  186 

retorts,  213.  235 
its  careful  application  to  glass, 

186,  190 
conduction  of,  601 

tested,  603 

reception  of  (uses),  603 
reflection  of  (uses),  603 
its  transmission  prevented,  222. 

229.  256 

Henly's  electrometer,  how  used,  458 
Hessian  crucibles,  297,  298 
Hood,  vapour,  22.  191 

portable,  191 
Hot  air,  a  heating  agent,  140 

procured,  140 

Hydrogen  gas  prepared  and  experi- 
mented upon,  648 
Hydrometer,  66 
verified,  68 

precautions  in  its  use,  66 
Hygrometric  power  of  powders,  170 

Ignition,  appearance  of,  155 
of  bodies,  311 

in  vapours,  428 

India-rubber,  or  caoutchouc  connec- 
tors, 2 17.  .383.  506 
bottles,  sheets,  &c.,  218.  373. 
384.  510 
4  L 


India-rubber,  method  of  expanding, 

by  ether,  220 
Indigo  sublimed,  238 
Inductive  practices,  a  course  of,  620s 
Infusion,  177.  203. 629 
Ink  for  writing  upon  glass,  605 
Insolubility,  indications  of,  181 
Insulation,  electrical,  492 
Iron,  its  influence  in  decompositions, 
326 

its  magnetism  examined,  619- 

cement,  505 

retorts,  236,  237 

tubes,  317 

filings  cleansed,  175 

Jackets  to  crucible,  305 
Jar,  Leyden,  453 

examined,  453 
substitute  for,  459 
Jars  for  gases,  334 

precipitation,  240.  181 
solutions,  181 
capped,  335 
,     cleansed,  559 
deflagrated,  334 
graduated,  88.  348 
plain,  334.  355 
filled,  339 
stoppered,  334 
transfer,  335 

filled,  341.  355 
their  stoppers  loosened,  565 
Jet  of  the  blow-pipe,  119 
Joining  of  glass  tubes,  539 
Joints  luted,  496.  501 
Junctions  rendered  tight  by  luting,  501 
hot,  rendered  tight,  503 
secured  by  soft  cement,  509 
of  apparatus,  226.  228.  230. 386 
tubes,  217.  318 

Kerr's  generating  gas  tube,  438 

Laboratory,  its  arrangement,  17,  18 

cleanliness,  554 
Lamination  of  metals,  175 
Lamp  furnace,  Cooper's,  321 
Lamps,  109 

Argand,  115.  188.  213.  320 

double  wicked,  116 
chemical,  114 
gas,  117 
oil,  115.  190.  213.  320 

trimmed,  116 

Lamps,  spirit,  110.  114.  304.  322 
its  "heat,  111 
large,  112.  304 


682 


INDEX. 


Lamps,  spirit,  Phillips's,  113 

for  blow-pipe,  123 
Lead,  leaf  and  sheet,  its  uses,  599 
precipitated,  246 
white  (lute),  505 
Leaf  metals,  uses  of,  599 
copper,  600 
zinc,  600 

Leaks  in  lutings  discovered,  510 
Leeson's  blow-pipe,  134 
Leslie's  specific  gravity  apparatus,  58 
Ley  den  jar,  453 

charged  from  the  elec- 

trophorus,  461 
examined,  453 
substitute  for,  459 
Lime,  carbonate  of,  precipitated,  246 
phosphate  of,  306] 
lutes  with  egg1,  &c.,  504 
Line  of  numbers,  Gunter's,  585 
Linseed  meal,  506 

oil,  for  batlfs^l39 
Liquids,  adjusted?«48.  195 
heated  in  tubes,  64.  416 
introduced  into  bulbs,  63 
measures  for,  74 
measured,  76 
poured,  193.  212 
transferred,  195 
their  specific  gravity  ascertain- 
ed, 60 

volatile,  weighed,  52 
weighed,  47 
Litmus  paper,  285 

preserved,  287 
used,  288 

Lixiviation,  304.  262 
Loosening  of  stoppers,  564 
Lute,  prepared,  496.  501 
applied,  497 

its  contraction  in  the  fire,  498 
Luted  vessels  dried,  497 

repaired,  498 
their  liabilities,  499 

in     the 

fire,  500 

supported  in  the  fire, 

235.  50-1 
Lutes,  495.  664 

almond  paste,  506 

bladder,  505 

caoutchouc,  506 

caustic  lime  and  white  of  egg, 

504 

fat  lute,  502 
fusible  lutes,  502 
iron  cement,  505 
linseed  meal,  506 
paper  and  paste,  505 


Lutes,  Parker's  cement,  503 

plaster  of  Paris,  503 

Stourbridge  clay,  496.  501 

white  lead,  505 

Willis's  lute,  502 

Windsor  loam,  502 
Luting,  495.  499.  501.  664 

of  joints,  501 

leaks  in,  discovered, 
510 

guarded  by  canvass,  499 

Maceration,  304 
Magnetic  needles,  616 

made,  619 
Magnetism,  616 

its  presence  ascertained,  616 
Magnets  made,  619 
Management  of  gases,  329 

heat,  91.  625 

Manipulation,  pneumatic,  329.  648 
Marcel's  blow-pipe,  133 
Marking  of  tubes,  78.  80.  447 
Masks  for  the  face,  611 
Masses  broken,  161 
Measurement  of  gases,  347.  361.  655 

Squids,  74.  77 
Measures,  74.  78.  624 
for  gases,  76.  352 
liquids,  74.  78.  90 
mercury,  84.  86 
graduation  of,  75 
tables  of,  91 
cubic  inch,  76 
pint,  74 
graduated,  77 
verified,  75.  77 
Measuring,  74.  347 

practices,  624.  655 
Membranes  permeated  by  gases,  134 

372,  373 

Mercurial  bath,  138 
gasometer,  366 
thermometer,  139.  144.  150. 

152 
trough,  23.  333.  354.  432 

its  jars,  334.  355.  362 
cleansed,  568 
dispensed  with,  433 
tube  receiver,  43 2 
Mercury,  weight  ofj  77  • 

its      influence, 

354.  356 
its  films,  83.  571 

their  effect,  357.  571 
cleansed,  568 
purified,  570.  574, 
surface  observed,  82 
weight  adjusted,  79.  84 


INDEX. 


683 


Metal  baths,  139 
tiibes,317 

tubes  heated,  318.  320 
Metallic  crucibles,  300.  303 
Metals,  broken,  163 

comminuted,  174.  628 
granulated,  174.  629 
leaf,  their  uses,  599 
precipitated,  246.  488 
reduced,  315 
sheet,  their  uses,  599 
Method,  rules  relating1  to,  575 
Mineral  water  evaporated,  279 

secured  by  soft    ce- 
ment, 508 
Mirrors  made,  612 
Miscellanea,  667 

Mixture  effected  in  a  filter,  254 
in  a  mortar,  165 
by  sieves,  171 
in  tubes,  414 
of  fluids,  244 
gases,  389 
refrigerating-,  220 
Mortars,  25.  157 

their  material,  157 
form,  158 
uses,  160.  627 
bodies  broken  in,  161 

pulverised  in,  164 
dissolved,  in,  183 
agate,  160 
iron,  157 

its  uses,  157 
porcelain,  158 

exanffied,  158 
porphyry,  159 
for  diamonds,  170 
cleansed,  567 
Muriatic  a*eid,  its  use  as  a  solvent, 

199 

gas  collected  in  bot- 
tles, 375 

gas  condensed,  445 
dissolve,  386 
prepared        and 
experimented 
with,  652 

Naphthaline,  purified  in  tubes,  451 
Needles,  magnetic,  495.  616.  619 
Neutral  precipitations,  289 
Neutralization,  289.  641 
JMfcre  (flux),  313 
Nitric  acid  distilled,  213 

its  use  as  a  solvent,  199 
oxide   gas,  prepared  and  ex- 
perimented with,  655 


P 


Nooth's  apparatus,  389 

Note  book,  laboratory,  29.  576 

Oil  as  fuel,  115 
lamps,  115.  190 

Oiled  silk,  its  use,  372.  392 

Oils  filtered,  256 

Olefiant  gas,  prepared  and  experi- 
mented with,  650 

Oxides  deoxygenated,  315 

reduced  in  tubes,  327 

Oxy-alcohol  blow-pipe,  133.  370 

Oxy-hydrogen  blow-pipe,  134 

Oxygen  prepared  in  tube  retorts, 
431.  654 

Oxygenation  of  metallic  solutions, 
201  :- 

Paper,  uses  of,  44.  141.  594 

and  paste  for  joints,  505 

vessels  covered  with,  267.  596 

cones  and  covers,  256.  267. 597 

filtering,  248 

funnels,  596 

handles  for  hot  tubes,  416.  527 

Ktmus,  285 

pasted,  506.  596,  597 

string,  598 

tubes,  384.  595.  628 
*     turmeric,  285 

vessels,  594 

waxed,  595,  596 
Parker's  cement,  503 
Paste  and  paper  for  junctions,  505 
Pasted  paper,  506 
Pepys'  gas-holder,  368 

gas  transferrer,  359 

mercurial  gasometer,  3$6 
Pestle,  its  form,  158 

use,  161,  165 

Phosphorescence  observed,  614 
Phosphorus  bottle,  28,  29 
Phillips' s  precipitating  glasses,  181. 
240 

spirit-lamp,  113 

Pik  voltaic,  (see  Voltaic  pile)  469 
Pint  measures,  74 
Pipes  of  paper  for  steam,  141.  596 
Plaster  of  Paris,  503 

rendered  air  tight,  503 
Plate  copper,  600 

zinc,  600 

Plates  of  glass,  270.  275.  336.  598 
Platinum,  influence  of  no  combina- 
tion, 326 

cleansed,  567 

divided,  176 

capsules,  300 


684 


INDEX. 


Platinum  crucibles,  300.  302 
crucibles  cleansed,  56T 
foil,  112.  600 
spatulas,  45.  169.  248 
spongy,  176 
tubes,  317 

heated,  322,  323 
wires  sealed  into  tubes,  539 
Pneumatic  manipulation,  329.  431. 

648 

in  tubes, 
420.  431. 
659 

apparatus  connected,  376 
jars,  334.  341 
joints,  tightness  of,  385 
trough,  330.  431.  555 

manipulation    of,     (see 

Gases) 
material   of,    331,  332. 

555 
mercurial,  333,  334 

cleansed,  568 
level  of  water  in,  351.  342 
small,  333.  340.  431 
Poles  voltaic  (see  Voltaic  poles),  474 
Porosity  of  earthenware  prevented, 

317.  502 
Pouring  without  loss,  193.  259 

by  rod,  193.  254 
Powders  dried,  280 

fine  and  coarse  separated,  171 
hygrometric,  170 
introduced  into  flasks,  192 
mixed,  171 
separated,  171 
transferred,  45,  169.  192 
washed,  172 
weighed,  44,  192 
fineness  judged  of,  167 
their  specific  gravity  ascertain- 
ed, 60 

Practices,  a  course  of,  620 
Precipitant,  240 

quantity  required,  242.  244 
Precipitating  glasses,  240 
Precipitates,  240 

collected,  258.  283 
dried,  261.  281,  282 
in  tubes,  430 
filtered,  254 
washed,  254.  260  , 
Precipitation,  240.  414.  635 
effected,  242.  245 
facilitated,  245 
in  tubes,  414 
'  neutral,  290 
precise,  24l 


Precipitation,  precautions,  244 
rules  relating  to,  577 
tests  of,  241 

vessels  required  for,  240 
voltaic  (Wollaston's),  247.  488 
of  carbonate  of  lime,  246 
chloride  of  silver,  245 
ferro-prussiate  of  iron,  245 
metals,  246 

sulphate  of  baryta,  245 
Preservation  of  bodies  in  tubes,  446. 

530 
Pressure  on  gases,  349 

corrections  for,  400 
Production  of  gas,  337 
Promoters  of  vaporization,  214 
Proportional  numbers,  585 
Proportions,  equivalent,  584 
Prussian  blue  precipitated,  245 
Pulverization,  coarse,  163 
fine,  164 

by  cylinder,  169.  221 
at  low  temperatures,  168 
fine,  appreciated,  167 
for  analysis,  169,. 
precautions,  168.'  170,  171 
Purification  of  mercury,  570 

of  iron  filings,  175 
Putty,  503 

Pyroligneous  ether,  114 
Pyrometer,  Daniell's,  155 
Wedgwood's,  155 

Quill  feathers,  uses  of,  255 
tube,  4  13^. 


worked,  523.  543 

Rack  for  tubes,  25.  414 

Rays  of  the  sun,  their  power,  20. 

615 
Receivers  for  condensation,  216.  .224 

volatile  products,  223 
tube,  419.  421.  431.  528* 

^''for  sublimation,  426 
mercurial  tube,  432 
Reception  of  helit,  603 
Rectification  in  tubes,  423 
Reduction  of  metals  by  charcoal,  315 

oxides  in  tubes,  327 
Refrigerating  mixture  made,  220 

guarded,  221 
Refrigeration,  cautions  in  applying, 

230 
in  distillation,  207.   216.    220. 

226.  234 

in  tube  sublimations,  426 
on  retort  neck,  225 


INDEX. 


685 


Reflection  of  heat,  uses  of,  603 
Regulations  as  to  cleanliness,   553. 

567 

Removal  of  stoppers,  562.  565 
Residual  charge  of  a  battery,  459 
Resin  removed  from  glass,  558 
Retention  of  heat,  141.  144.  229.  256,. 
Retort  caps,  380 

affixed,  381.597 
their    place    supplied, 

382 

stands,  48.  115.  188 
Retorts,  208.  235.  419.  430 
broken,  useful,  239:  545 
gas  evolved  from,  337 
for  exhaustion,  208.  393     Jl 
glass,  208 

their  form,  208.  393 
thickness,  209 
coated,  235.  496 
heated,  235 
necks  elongated,  224 
bent,  230 
earthenware,  236 

l 

iron,  236,  237 
tubes,  419.  431.  528 
tubulated  and  plain,  209 
capped,  380 
charged,  211,  212 
cleansed,  561 
coated,  235.  496.  499 

supported  in  the  fire, 

235. 501 
dried,  .560,  561 
heated,  213 
Rings  listed,  use  of,  48 

furnace,  101 
Rock  crystal,  surface  of,  in  tubes, 

325  .     •&    ,* 

Rod,  glass,  cut,  518.  544 
Rods,  glass,  183.  518 

their  use   in    pouring, 

193 
transference  of  liquids 

by,  195 

Roman  cement,  503 
Rules  for  young  experimenters,  575 
relative  to  cleanliness,  553.  566. 

575 

relative  to  precipitates  and  test- 
ing, 577 

Safety  tube,  231 

of  Hassenfratz,  387 

Welter,  231  - , 
Sal  enixum,  314 

£alts  favour  voltaic  decomposition, 
483 


Sand,  kind  required,  27.  101 
Sand-bsAh,  99.  135.  186 
Sand-fot,  101.  238,  239 
Saturation,  indication  of,  185 
Scale  of  chemical  equivalents,6275581 
its  construction,  585 
use,  586 
errors,  590 
Scales  of  thermometers,   compara- 
tive, 146 

Scratching,  diamond,  78.  477 
Screens  for  the  face,  611 
Sealing  of  tubes,  523 

hermetically,  421. 

530 

Selection  of  solvents,  197 
Separation  of  fluids,  262.  638 
powders,  171 
precipitates,  247.  259. 

637 

by  crystallization,  264. 269 
Separators,  263.  530 
Sheet  lead,  its  use,  599 
metals,  uses  of,  599 
caoutchouc,  218.  384.  220 
Shelves,  their  arrangement,  24 
Shot  for  cleansing  bottles,  557 
Sieve,  171 

mixtures,  171 
Sifting,  171 
Silicia  divided,  174 
Silk,  insulations,  precautions,  494 

valve,  392 

Silliman's  blow-pipe, 
Silver  basins,  181 
divided,  176 
crucible,  301 
becomes  brittle,  265 
precipitated,  246 
Silvering  glass,  612 
Singers's  electrometer,  463 
Sink,  its  arrangements,  23 

its  accompaniments,  555 
Sme^ing  trough  a  tube,  605 
Soft  brick,  601 

cement,  272,  507 

mineral  waters  confin- 
ed b,y,  508 

Softness  of  hot  glass,  515 
Solar   radiant   matter,   its    powers, 

20.615 
Solid  bodies,  their  specific  gravity 

determined,  53.  58 
Solubility  affected  by  presence  of 

substances,  200 
conferred  by  tartaric  acid,  201 
increased  by  heat,  180 
indication  of,  178 
Solution,  177.  629 


686 


Solution,  its  uses, 
els  requ: 


177 

vessels  required  for,  1 
in  a  mortar,  183 
acids,  199 
alcohol,  191 
alkalies,  200 
water,  178 
by  heat,  184, 
of  carbonates,  193 
chlorine,  389     >?- 
gases,  385,  389 

in  tubes,  439 
muriatic  acid  gas,  386  ^ 
organic  substances,  203 
"on  a  small  scale,  195.  416 
of  two  kinds,  177 
baths,  137 

Solutions,  boiling  points  of,  137 
saturated,  obtained,  185 
metallic,  201 
deoxygenized,  202 
oxygenized,  201 

Solvents,  their  selection,  197.  268 
Spatulas,  45.  169.  248 
Specific  gravity  ascertained,  53 
bottles,  60 
bulbs,  62.  68.  65 
of  liquids,  60.  66 
porous  bodies,  58 
powders,  58 
solids,  53 

Spikes,  their  places  and  use,'  25 
Spirit-lamp,  110 

large,  112,  113.  304     '*i 
Phillips's,  113 
its  heat,  111.  304 

Standards  of  measurement,  74. 76. 91 
Stands  for  retorts  and  flasks,  48,  188 
Steam,  its  heating  powers,  141 
apparatus,  141 
bath,  142 
boiler,  144 
chamber,  142 

Still,  101.  206  •       4 

Stirrers,  glass,  183.  518 
Stones,  breaking  of,  161 
Stop-cocks,  376.  379 
collars  of,  378 
examined,  377.  383 
tightness  of,  382 
Stoppers,  furnace,  94 

glass,  210.  234.  335.  549 
ground,  552 , 
examined,  210 
for  fuijnels,  262 
loosened,  562.  565 
Stourbridge,  clay  lute,  298.  496,  501 
•Strength  of  glass  tubes,  397 


paper,  598 

Sublimatm,  205,  237.  425.  632 
vessels  required  for,  237 
in  tubeSj*  425  .    <|C 
of  indigo,  238 
Subliming  tubes,  425 
*  Substances,  broken,  161 
heated,  311 

in  lamp  flame,  111 
preserved  in  tubes,  446.  530 
Sulphate  of  baryta  precipitated,  245 
Sulphuric  acid  a  desiccator,  273.  408 
distilled,  215 
exactly  precipitated,  243 
gas  dried  over,  408 
'llts  use  as  a  solvent,  199 
Sulphurous  acid  condensed  in  tubes, 

444 

distilled,  217.  422 
receivers  for,  422 
Supports  for  apparatus,  48.  233 
crucibles,  304.  307 
blow-pipe  experiments, 

127 
Surface  for  Decomposition  extended 

in  lubes,  325 
Synoptic   scale   of  equivalents,  (see 

Scale)  581.  590 
Syphon,  259 
made,  528 
of  cotton,  261 
its  use,  259 
decantation  by,  259 
Syringe,  its  use,  390.  396 
examined,  391 
tube,  263.  529 

Table  blow-pipe,  129.  511 

how  used,  129 
'  funglice,  21.  97.  305 
of  boiling  points  of  solutions,  137 

chemical  equivalents,  592 
measures,  91 
weights,  73 
Tables,  laboratory,  22 
Tar  removed  from  glass,  558 
Tartan'cacid,  solubility  conferred  by, 

201 
Taste  as  an  indication  of  solubility, 

178 

Temperature  estimated,  145.  155 
of  gases,  349 
gas  corrected  for,  398 
Temporary  .blow-pipe,  119.  130.  543 

flue,  97 
Test  glasses,  240 

cleanliness  of,  554 
cleansed,  527 


INDEX. 


687 


Test  papers,  284.  641 

their  indications,  288,  289 

use,  289 
preserved,  287 
solutions,  284,  295.  641 
tubes,  414 
Testing,  241.  414 
Tests,  coldured,  284.  641 
Thermometers,  144.  587 

temperature  observed  by,  13 

147.  150.  627 
air,  152 
alcohol,  149 
chambered,  152 
changes  of,  149 
compared,  147 
differential,  154 
errors  of,  151 
graduation  of,  145 
mercurial,  139.  145.  149 
examined,  145 
its  indications,  149 
observed,  152 
open  and  closed,  150 
Tightness  of  pneumatic  joints,  382 
Tin  foil,  its  uses,  599 
Tobacco  pipe  used  as  a  crucible,  302 
Tongs,  102.  311 
Took,  laboratory,  26 
Tow,  its  uses,  556.  559 

wrapped  round  glass,  432 
Transfer  jar,  335 

filled,  341 
Transference  of  gas,  341.  343.  394 

over    mercury, 

356.  358 
over  water,  341. 

343 
from  jars,  343 

tubes,  345 
into  exhausted 

vessels,  349 
of  liquids,  ^93.  195 

powders,  45 
Transferrer,  gas,  358 
Trivets  for  troughs,  331.  555 
Trough,  mercurial,  333.  355.  432 

its  place,  23 

pneumatic,  329.  431.  555 
its  place,  26 
manipulation  at  (see 

Gases) 

varieties  of,  330.  431 
mercurial,  333.  432 
its  waters  changed, 

555 

Tube  combinations,  327.  647 
decompositions,  325.  646 
operations  (furnace),  316.  646 


Tube  chemistry,  195.  413.  658 
chemistry,  practices,  658 
condensation,  425 
desiccation,  427 
digestion,  416 
distillation,  419 

gaseous,  421. 431 
in  vacuo,  424 

ebullition,  under  pressure,  417 
gases  collected,  432.  660 
condensed,  440 
dissolved,  439 
examined,  434 
ignition  in  vapours,  427 
pneumatic  manipulation,  431 
precipitation,  414 
preservation  of  substance,  446 
rectification,  423 
chemistry,  separation,  415 
solution,  415 
sublimation,  425 
testing,  414 
washing,  415 
apparatus,  413 

for  distillation,  418 
air  jars,  431 
evaporators,  430 
feeding,  232 
funnel,  419.  528,  529 
handles,  416 

Kerr's  generating  gas,  438 
lamp-furnace,  320 
pneumatic  apparatus,  431.  659 
quiU,  413 
rack,  25.  414 
retort,  419.  430,  431 
receivers,  419.  421.  431.  528 
supported,  420 
mercurial,  432 
of  safety,  Hassenfratz's,  387 

Welter's,  231 
separator,  263.  530 
stand,  414 
syphons,  259.  528 
syringes,  258.  263.  529 
test-glasses,  414 
water-bath,  136 
Woulfe's  apparatus,  439 
of  animal  intestine,  384 
Tubes,  caoutchouc    (flexible),  218. 

384.  319 
copper,  318 
earthenware,  316 
glass,  318.  413 

strength  of,  396.  440 
cut,  518.  544 
heated,  320.  323.  511 
cased  with  foil,  324.  600 
green  glass,  318 


688 


INDEX. 


Tubes,  iron,  317 

metallic,  317.  384 

heated,  320 
1  paper,  384.  447.  595 
platinum,  317 
plumbago,  317 
bent,  516.  519 
cleansed,  558 
closed,  4 13.  523 

by  the  fiijjger,  346 
temporarily,  440 
coated  or  luted,  316.  499 
connected,  318 

'••contracted,  224,  421.' 5^9-  531 
cut,  518.  544 
graduated,  77 
heated,  96.  320.  511 

in  the  middle,  511.  520- 

524 
*  at  the  ends,  513.  522 

Supported,  416 
marked,  78.  80 
made,  523.  527.  537 
sealed,  523.  529 

i   hermetically,  530 
strength  of,  397 
supported,  317 
weighed,  45 
for  gases,  336.  383 
digestion,  416 
voltaic  decompositions,  479. 

541 

uses  of,  as  bottles,  446 
in  mixing,  244 
substances  preserved  in,  446 
liquids  heated  in    them  under 

pressure,  64.  416 
their  contents  mixed,  414 
transference  of  gas  in,  345 
capillary,  made,  528 
wires  sealed  into,  540 
generating,  432.  437.  439 

gases  examined  in, 

433 

Tubulated  retorts,  209 
Turmeric  paper  prepared,  287 
uses,  288 
precautions,  290 
Turpentine  removed  from  glass,  558 

Ure's  eudiometer,  457 

steam  apparatus,  143 
Uses  of  copper  wire,  598 
corks,  593 
glass  plates,  598 
leaf  and  sheet  metals,  599 
paper,  595 

reflective  and  receptive  pow- 
ers, 603 


/  rses  of 


.... 


Windsor  b 


rick,  601 


Valve,  silk,  392 
Vaporization  promoted,  214 

crystals  obtained  by,  272 
Vapour  hood,  "22.  191 . 
Vapours,  bodies  heated  in,  428 
conveyed  away,  191 
decomposed  in  tubes,  325.  428 
heated  inches,  319.  325.  428 
ignited  in  simple  tubes,  427 
.    their  volumes,  592 
Varnish  for  trivets,  555 
Ventilation  of  the  laboratory,  20 
Vessels  of  paper,  594     ^ 
covered,  278 

with  paper,  267 
exhausted  of  air,  390 

precautions, 

391 

graduated,  77 
luted  or  coated,  497  " 
Volatile  bodies  confined,  422 
distilled,  217 
Voltaic  contact,  477 

communication,  473.476.  486 
decomposition,  475. 479. 481 
of  fluids,  479 
favoured,  483 
gases,  491 
in    platinum   cap- 
sules, 480 
tubes,  479 
separate  vessels, 

483 

tubes  for,  540 
gases      collected, 

480 

interfering  circum- 
stances, 481 
precipitation,  Wollaston's,  247. 

488 

battery,  469 
discharge  through  charcoal,  471 

heat  of,  491 

pair  of  plates  arranged,  487 
pile,  469.  663 

arrangement  of,  485 

its  parts  connected,  474. 

486 

constructed  quickly,  485 
small,  485 

temporary,  485.  487 
Wollaston's,  487 
charge  for,  469 
put  into  action,  469 
examined,  471 
its   decomposing   powers 
applied,  479 


INDEX. 


689 


Voltaic  pile,  raised  at  intervals,  484 
poles  of,  474.  486 

their  nature  and 
extent,  474. 486 
handled,  478 
quantity  and  intensity, 

486 
poles,  474 

distance  from  each  other, 

475.  482 
their  material,  475 

surface,  476.    478. 

480 

thickness,  474.  478 
troughs  connected,  473.  486 
Volume  of  gas  observed,  347. 350 
corrected,  397 

.for  moisture,  403 
pressure,  400 
temperature,  398 
Volumes  of  gases,  592 

Warm  air  chamber,  280 
Washers,  378 
Washing  bottle,  258 

by  decantation,  260.  637 
of  powders,  172.  637 
precipitates,  254.  260. 

637 

Water  distilled,  important,  27.  193 
its  use  as  a  solvent,  178 
decomposed  in  tubes  by  heat, 

326 

evaporated  in  tubes,  430 
weight  of,  75.  91 
baths,  135 

uses  of,  136 
arrangement  of,  136 
trough,  pneumatic,  26.  329.  555 
boiling  heat  varies  with  depth, 

146 

Wax,  yellow,  507 
Waxed  paper,  595,  596 

twine,  183 

Wedgwood's  basins,  181 
crucibles,  297.  299 
.    pyrometer,  155 
Weighing,  operations  of,  40.  43.  56. 

72.  621 
practices,  621 


Weighing  of  changeable  substances, 

50 

effect  of  the  air's  buoyancy,  53 
of  fluids,  47 
gases,  403.  409 
heated  substances,  43 
pieces,  40 
powders,  44.  311 
tubes,  46 
volatile  fluids,  52 
in  vessels,  47.  87 

Weight  of  measures  of  mercury,  77 
water,  75.  77 

Weights,  examination  of,  39 
handled,  41,  42 
required,  33 
small,  33.  71.  73 
substitutes  for,  73 
table  of,  73 

Welter's  safety  tube,  231 
White  flux,  312 

lead  (lute),  505 
Willis's  lute,  502 
Wind  furnace,  96.  102 
Windows  of  the  laboratory,  19 
Windsor  brick,  601 

loam  (lute),  502 
Wine  distilled,  225 
Wiping  sticks,  556 
Wire,  copper,  uses  of,  598 
Wires  amalgamated,  477 
of  the  eudiometer,  453 
sealed  into  tubes,  540.  542 

eudiometer     tubes, 

542 

for  cleansing,  556 

Wollaston's  scale,  (see  Scale  of  equi- 
valents) 581 
Wooden  blocks,  25 
Working  of  glass,  511 
Worm  tub,  206 
Woulfe's  bottles,  230.  385 

replaced  by  tube,  439 
Writing  upon  glass,  78.  447.  604 

Yellow  wax,  507 

Zinc  foil,  600 

plate,  485.  600 
pulverized,  168 


THE  END. 


4M 


Philadelphia,  February,  1831. 
Just  Published,  by  Carey  6f  Lea, 

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THE    OPERATIVE    MECHANIC 


AND 


COMPREHENDING    A 

COMPLETE  AND  SYSTEMATIC  DEVELOPMENT 

BOTH    OF    THE 

THEORY  AND  PRACTICE  OF  THE  PRODUCTIVE  ARTS 

IN  THEIR  PRESENT  STATE  OF  UNRIVALLED  PERFECTION; 
AND  EXHIBITING 

THE  ACTUAL  CONSTRUCTION  &  PRACTICAL  USES 

OF  ALL  THE 

MACHINERY    AND    IMPLEMENTS 

NOW  USED  IN  GREAT  BRITAIN, 

With  the  real  processes  adopted  in  perfecting  the  National  Manufactures  of  every 

Description. 


By  JOHN  NICHOLSON,  Esq.  Civil  Engineer. 


SECOND  AMERICAN  EDITION  FROM  THE  LAST  LONDON,  WITH  ADDITIONS  ADAPTED 

TO  THIS  COUNTRY. 


THE  OPERATIVE  MECHANIC  will  display,  in  a  cheap  form  and  in  a  correct 
and  comprehensive  manner,  the  actual  state  of  Scientific  Improvement  as  it  is 
at  present  applied  to  the  productive  industry  of  this  Empire;  as  it  is  actually 
found  in  Workshops  and  Manufactories  of  the  highest  character.  It  conveys 
every  desirable  information  relative  to  Engines  and  Constructions  particularly, 
and  to  all  branches  of  the  Metallic,  Woollen,  Cotton,  Linen,  Filk,  Porcelain, 
and  other  important  Manufactures,  and  is  equally  valuable  to  the  Intelligent 
Workman,  the  Scientific  Master  Manufacturer,  and  the  ingenious  Projector 
of  important  Improvements.  It  was  planned  under  the  auspices  of  Dr.  BIRK- 
BECK,  President  of  the  Mechanics'  Institution  of  London,  and  executed  at  his 
suggestion  by  Mr.  John  Nicholson,  a  gentleman  considered  as  especially  qua- 
lified for  this  duty — by  education  under  a  father  whose  Journal  of  Science' <$ 


Natural  Philosophy,  and  various  other  highly  esteemed  works,  had,  for  half  a 
century,  placed  him  at  the  head  of  the  scientific  world — hy  very  great  experi- 
ence in  the  conduct  and  arrangement  of  many  considerable  manufacturing  es- 
tablishments— and  by  all  those  qualities  of  accuracy  and  integrity,  which  were 
so  necessary  to  the  perfect  execution  of  such  a  work.  To  these  personal  qua- 
lifications, Mr.  Nicholson  superadded  an  extensive  acquaintance  among  Scien- 
tific Mechanics  of  the  first  class,  of  whose  correspondence  he  enjoyed  the  ad- 
vantage; and  Dr.  BIRKBECK  himself  contributed  some  Chapters  on  branches 
within  his  own  particular  experience. 

*#*  The  whole  is  illustrated  by  upwards  of  ONE  HUNDRED  Copper-plate 
Engravings,  comprising  ONE  THOUSAND  Subjects  of  MECHANICAL  SCIENCE, 
and  is  complete  and  strongly  bound  in  2  two  large  volumes,  octavo. 

The  Reader  is  requested  to  peruse  attentively  the  following  very  brief  and  imperfect  Outline 
of  the.  TABLE  OF  CONTENTS  of  NICHOLSON'S  OPERATIVE  MECHANIC. 


Introductory  Chapter.  ON  MATTER.  Of  the 
action  of  Forces — Friction — Gravity,  &c. 

MECHANICAL  POWERS.  The  Lever — Wheel 
and  Axle — Fully — Inclined  Plane — 
Wedge — Screw — Simple  Combinations, 
&c. 

Practical.  ON  MILL  GEERING.  Definition 
of  Terms — To  describe  the  Cycloid  and 
Epicycloid — the  Teeth  of  Wheels — Spur 
Geer — Bevil  Geer,  &c. 

Couplings*  Square  Couplings  with  Double 
Bearings— Clutches  or  Glands — Boring 
Mill  Clutches — Self-easing  Coupling — 
Bolton  and  Watt's  Coupling  Link — 
Hook's  Universal  Joint— Double  Univer- 
sal Joint,  &c. 

Disengaging  and  Re-engaging  Machinery. 
Sliding  Fully— Fast  and  Loose  Pulley — 
Bayonet — Lever — Tightening  Ptoller — 
Friction  Clutch — Friction  Cone — ^Self- 
disengaging  Coupling. 

On  Equalizing  the  Motion  of  Machinery. 
Steam  Engine  Governor  — Water  Wheel 
Governor— Wind-Mill  Governor—Tacho- 
meter by  Donkin. 

General  Observations  on  Mill-Geering. 

Animal  Strength.  Immediate  Force  of  Men 
without  deducting  for  Friction — Perform- 
ance of  Men  by  Machines— Force  of 
Horses — Work  of  Mules—  How  Extraor 
dinary  Feats  of  Strength  may  be  per- 
formed by  Men  of  ordinary  Strength^ 

WATER.     On  Water  Mills  in  general. 

Undershot  Wheels.  Smeaton's  Experiments 
on — also  by  Lambert. 

Overshot  Wheels.  By  Burns — Smeaton's 
Experiment's  on — by  Burns,  without  a 
shaft — Chain  of  Buckets,  &c. 

Breast  Wheels,  in  vrhich    the  water   runs 
over  the   shuttle — Lloyd   and  Ostell's  — 
with  two  Shuttles— Barker's  Mill— Tide! 
Mills — Wheel-races  and  Water-courses —  j 
Mill-courses — Water-courses   and  Dams 
— Penstock — Pentrough,  by   Smeaton — 
by  Nouaille — Method  of  Laying  on  Water 
in     Yorkshire — Sluice-Governor—Rules 


for  constructing  Undershot  Wheels,  by 
Ferguson— by  Brewster. 

List  of  Treatises  on  Mill- Work,  &c. 

WIND.  Vertical  Windmills.  Post  Mill- 
Smock  Mill — Smeaton's  Experiments  ou 
— Modelling  of  Sails — Clothing  and  Un- 
clothing Sails  while  in  Motion — Baine's 
Sails — Equalizing  the  Motion  of  Sails  : 
with  eight  quadrangular  Sails. 

Horizontal  Windmills,  &c. 

Flour  Mills.  Mill-stones— Fenwick's  Ta- 
bles—Family Mill— Hand  Mill— Foot 
Mill— Kneading  Mill,  &c. 

STEAM.  Steam  Engine,  by  Savary — by 
Newcomen — by  Watt— by  Hornblower — 
by  Woolf- Bell-Crank  Engine— Vibratory 
Engine — Rotatory  Engine — High  Pres- 
sure Engine — Lean's  Reports — General 
Observations. 

Broivn's  Vacuum;  or,  Pneumatic  Engine. 

Rennie  on  the  strength  of  Materials. 

Hydraulic  Engines.  The  Tympanum— De 
la  Faye's  Wheels— The  Noria— The  Per- 
sian Wheel — Paternoster  Work — Hiero's 
Fountain — Darwin's  Engine — Hungarian 
Machine  — Boswell's  Improvement  of  do. 
— The  Spiral  Pump  at  Zurick—  Desagu- 
lier's  Drawer  and  Bucket— Sargeant's 
Machine — Dearborn's  Pump  Engine — 
Archimedes'  Screw — Pressure  Engine — 
List  of  Treatises  on  Hydraulics. 

Pumps.  The  Common  Pump — Pump  with 
little  Friction— Suction  Pump,  by  Taylor 
— Todd's  Improvement  of  the  Common 
Pump — Lifting  Pump— Forcing  Pump — 
Ctesebius'  Pump — Steven's  Pump-Ty- 
ror's  Pump — Franklin's  Pump— W.  Brun- 
ton's  Force  Pump — Smeaton's  Three- 
Barrel  Pump— Chain  Pump,  by  Coles — 
Hand  Pump  by  Martin,  by  Jekyl — 
Clarke's  mode  of  applying  Manual  Force 
to  Pumps— Pump  Piston's  by  Bonnard,  by 
Belidor-Fire-Engine:  Newsham's,  Rown- 
tree's. 

Simple  Machines.  Jacks  for  Lifting  Weights 
&c. — -Cranes — Presses  Cyder  Press — 


Screw  Press,  for  Paper-Mill — Peek's 
Packing-  Press — Bramah's  Hydrostatic 
Press. 

Printing  Presses  and  Machinery,  &c. 

Pile  Engines,  by  Valou— by  Bunce. 

File- Catting  Machine.  Ramsden's  Dividing 
Machine — Lathes  and  Turning  Appara- 
tus, by  Maudesley,  by  Smart,  &c. 

Manufacture  of  Metals.  Iron.  The  Ore — 
Qualities—  Furnaces— Roasting — Smelt- 
ing—Blast, regular— Intermediate  Cylin- 
der—Water Regulator— Carron  Works- 
Conversion  of  Pig  Iron  into  Wrought— 
Shingling — Welding— Common  Harden- 
ing  Case  Hardening Refining  Fur- 
naces— Puddling  Furnace — Tilt  Ham- 
mar — Forge  Hammar— Re-manufactur- 
ing Iron— Tables  of  the  Weight  of  Bars, 
<fec. 

Steel.  Cementation — Converting  Furnace  ; 
Blistered  Steel:  Sheer  Steel:  Cast  Steel: 
Tempering  Steel:  Hardening  Steel,  &c. 

Wire.  Rolling:  Drawing:  Draw-bench: 
Draw  Plates:  Annealing:  M.  M.  Mon- 
chel's  Manufactory:  Woollaston's  Expe- 
riments, &c. 

Lead.  Smelting  the  Ore:  Reverberatory 
Furnace:  Qualities  of  the  Ore:  Extract- 
ing Silver;  Pig  Lead:  Sheet  Lead:  Lead 
Pipes:  Wilkinson's  Patent:  Plumbing: 
Tinning,  &c. 


MANUFACTURE  OF  FIBROUS  MATERIALS.-— 
Paper;  Cotton;  Wool;  Silk;  Flax; 
Weaving;  Hemp  and  Rope;  Temper- 
ing, &c. 

SUNDRY  MANUFACTURES.  Saw-Mills:  Bark 
Mill:  Oil-Mill:  Colour-Mill:  Indigo-Mill: 
Pottery  of  all  sorts,  &c. 

HOROLOGY.  Clocks.  With  Three  Wheels 
and  Two  Pinions,  by  Dr.  Franklin,  by  J. 
Ferguson:  for  exhibiting  the  Motions  of 
the  Sun  and  Moon,  the  Tides,  &c. — 
Striking  Part  of  an  Eight  Day  Clock: 
Curious  Clocks,  &c. 

Watches.  Description,  with  Figures:  Parts 
of:  Table  of  Trains:  Chronometer,  &e. 

Escapement.  Recoiling,  or  Crown-wheel, 
by  Gumming:  for  Watch,  by  Prior,  by 
Reid,  by  De  Lafons,  &c. 

Pendulums.  Mercurial,  by  Graham:  Grid- 
iron, by  Harrison:  Lever,  by  Ellicott: 
Tubular,  by  Troughton,  by  Reid,  by 
Ward:  Sympathy  of  the  Pendulums  of 
Clocks,  &c. 

Building.  Prefatory  Observations.  Mortar: 
Brick-making:  Masonry:  Bricklaying: 
Carpentry:  Joinery:  Plastering:  Slating: 
Plumbing:  Painting:  Glazing,  &c. 

Rail  Roads  and  Locomotive  Engines. 

APPENDIX.  The  Principles  of  GEOMETRV, 
MENSURATION,  &c.  Useful  Receipts,  &c. 

General  Glossary  of  Technical  Terms. 


GOLDSMITH'S  POETICAL  AND  MISCELLANEOUS  WORKS,  com- 
plete in  1  Yol  8vo. 

MOORE'S  POETICAL  WORKS,  complete  in  1  Vol.  8vo. 

SIR  WALTER  SCOTT'S  POETICAL  WORKS,  complete  in  1  Vol.  8vo. 

ELEMENTS  OF  RHETORIC,  comprising  the  Substance  of  the  Article  in 
the  Encyclopaedia  Metropolitana  :  with  Additions,  &c.  by  Richard  Whately, 
D-  D.  Arehbishop  of  Dublin. 

ROSS'  LATIN  GRAMMAR.  A  Short,  Plain,  Comprehensive,  Practical 
Latin  Grammar,  comprising  All  the  Rules  and  Observations  necessary  to 
an  Accurate  Knowledge  of  the  Latin  Classics,  having  the  Signs  of  Quantity 
Affixed  to  certain  Syllables,  to  show  their  Right  Pronunciation;  with  an 
Alphabetical  Vocabulary.  The  Ninth  Edition,  Revised  and  Improved,  by 
James  Ross,  LL.  D.  Professor  of  the  Latin  and  Greek  Languages,  North 
Fourth  street,  Philadelphia. 

Nequis  igitur  tanquam  parva  fastidiat  Grammatices  elemcnta. 

Pcrveniri  ad  summa,  nisi  ex  principiis,  non  potest.— Quaint. 

"Qui  discit,Bt  lex  ei  (otf)  in  possessionem, 

Et  non  discit,  fundamenta  Grammatices,  neque  intelligit, 

(Eft)  sicut  arator;  qui  agit  boves; 

Et  manus  ejus  (Est)  sine  baculo  aut  stimulo." 

GOLDSMITH'S  NATURAL  HISTORY,  Abridged  for  the  use  of  Schools, 
by  Mrs.  Pilkinton.  Revised  and  corrected  by  a  Teacher  of  Philadelphia. 
To  which  is  added  an  Appendix,  Exhibiting  the  Classification  0f  Linnaeus: 


and  a  number  of  Questions  to  aid  the  Preceptor  in  the  Examination  of 
Students.     Thirteenth   Edition. 

CLARK'S  CAESAR,  C.  Julii  Caesaris,  Quae  Extant,  Interpretatione  et  Notis 
Illustravit  Johannes  Godvinus,  Professor  Regius,  in  Usum  Delphini.  The 
Notes  and  Interpretations  Tranlsated  and  Improved  by  Thomas  Clark. 
Eighth  Edition. 

BARNES'  FAMILY  PRAYERS-  Prayers  for  the  Use  of  Families,  chiefly 
selected  from  various  Authors;  with  a  Preliminary  Essay:  together  with  a 
Selection  of  Hymns,  by  Albert  Barnes. 

LUTHER'S  SERMONS.  A  Selection  of  the  most  celebrated  Sermons  of 
Martin  Luther,  Minister  of  the  Gospel  and  Principal  Leader  of  the  Pro- 
testant Reformation.  (Never  before  Published  in  the  United  States.)  To 
which  is  prefixed  a  Biographical  History  of  his  Life. 

CALVIN'S  SERMONS.  A  Selection  of  the  most  celebrated  Sermons  of  John 
Calvin,  Minister  of  the  Gospel,  and  one  of  the  Principal  Leaders  in  the 
Protestant  Reformation.  (Never  before  published  in  the  United  States.) 
To  which  is  prefixed  a  Biographical  History  of  his  Life. 

GREAT  SYMPATHETIC  NERVE,  by  J.  R.  Manec,  D.  M.  .P  Lecturer 
on  Anatomy  and  Operative  Surgery  at  Paris.  Translated  and  corrected  by 
J.  Pancoast,  M.  D.  Drawn  on  Stone  by  P.  Ancora.  Highly  Varnished, 
on  Rollers,  and  Beautifully  Coloured. 

THE  CEREBRO-SPINAL  AXIS  OF  MAN,  with  the  Origin  and  First 
Division  of  its  Nerves.  From  the  French  of  M.  Manec,  D.  M,  P.  Lec- 
turer ©n  Anatomy  and  Operative  Surgery,  &c.  at  Paris.  Translated  and 
Revised  by  J.  Pancoast,M.  D.  Drawn  on  Stone  by  P.  Ancora,  Highly 
Varnished,  on  Rollers,  and  Beautifully  Coloured. 

BUFFON'S  NATURAL  HISTORY.  A  Natural  History  of  the  Globe,  of 
Man,  of  Beasts,  Birds,  Fishes,  Reptiles,  Insects,  and  Plants;  from  the 
Writings  of  Buffbn,  Curvier,  Lacepede,  and  other  Eminent  Naturalists. 
Edited  by  John  Wright,  Member  of  the  Zoological  Society  of  London.  A 
New  Edition,  with  improvements  from  Geoffry,  Griffith,  Richardson,  Lewis, 
and  Clark,  Long,  Wilson,  and  others.  With  Five  Hundred  Engravings.  In 
Five  Volumes. 

DEWEES'  BAUDELOCQUE.  An  Abridgement  of  Mr.  Heath's  Transla- 
tions of  Baudelocque's  Midwifery.  With  Notes,  by  William  P.  Dewees,  M. 
D.Lecturer  on'Midwifery  in  Philadelphia;  Member  of  the  Philadelphia  Medi- 
cal Society;  Mem.  of  the  Academy  of  Medicine;  Mem.  Amer.  Phil.  Soc. 
&c.  Third  Edition,  with  Additions.  Illustrated  with  Engravings 

EXTRAIT  MYTHOLOGIQUE.  A  L'Usage  des  Demoiselles.  Par 
Mlle.  Adele  Labruere. 

VADE  MECUM.  The  Devout  Christian's  Vade  Mecum:  being  a  Summary 
of  Select  and  Necessary  Devotions. 

MOORE'S  MELODIES.  Melodies,  Songs,  Sacred  Songs,  and  National 
Airs.  By  Thomas  Moore,  Esq. 


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